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Concepts in Objective-C ProgrammingContents About the Basic Programming Concepts for Cocoa and Cocoa Touch 7 At a Glance 7 How to Use This Document 7 Prerequisites 8 See Also 8 Class Clusters 9 Without Class Clusters: Simple Concept but Complex Interface 9 With Class Clusters: Simple Concept and Simple Interface 10 Creating Instances 10 Class Clusters with Multiple Public Superclasses 11 Creating Subclasses Within a Class Cluster 12 A True Subclass 12 True Subclasses: An Example 14 A Composite Object 16 A Composite Object: An Example 16 Class Factory Methods 20 Delegates and Data Sources 22 How Delegation Works 22 The Form of Delegation Messages 24 Delegation and the Application Frameworks 25 Becoming the Delegate of a Framework Class 26 Locating Objects Through the delegate Property 27 Data Sources 27 Implementing a Delegate for a Custom Class 27 Introspection 29 Evaluating Inheritance Relationships 29 Method Implementation and Protocol Conformance 30 Object Comparison 31 Object Allocation 34 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 2Object Initialization 35 The Form of Initializers 35 Issues with Initializers 36 Implementing an Initializer 38 Multiple Initializers and the Designated Initializer 40 Model-View-Controller 43 Roles and Relationships of MVC Objects 43 Model Objects Encapsulate Data and Basic Behaviors 43 View Objects Present Information to the User 44 Controller Objects Tie the Model to the View 44 Combining Roles 45 Types of Cocoa Controller Objects 45 MVC as a Compound Design Pattern 47 Design Guidelines for MVC Applications 50 Model-View-Controller in Cocoa (OS X) 52 Object Modeling 53 Entities 53 Attributes 54 Relationships 55 Relationship Cardinality and Ownership 56 Accessing Properties 57 Keys 57 Values 57 Key Paths 58 Object Mutability 60 Why Mutable and Immutable Object Variants? 60 Programming with Mutable Objects 62 Creating and Converting Mutable Objects 62 Storing and Returning Mutable Instance Variables 63 Receiving Mutable Objects 64 Mutable Objects in Collections 66 Outlets 67 Receptionist Pattern 68 The Receptionist Design Pattern in Practice 68 When to Use the Receptionist Pattern 71 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 3 ContentsTarget-Action 73 The Target 73 The Action 74 Target-Action in the AppKit Framework 75 Controls, Cells, and Menu Items 75 Setting the Target and Action 77 Actions Defined by AppKit 78 Target-Action in UIKit 78 Toll-Free Bridging 80 Document Revision History 83 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 4 ContentsFigures, Tables, and Listings Class Clusters 9 Figure 1-1 A simple hierarchy for number classes 9 Figure 1-2 A more complete number class hierarchy 10 Figure 1-3 Class cluster architecture applied to number classes 10 Figure 1-4 An object that embeds a cluster object 16 Table 1-1 Class clusters and their public superclasses 11 Table 1-2 Derived methods and their possible implementations 13 Delegates and Data Sources 22 Figure 3-1 The mechanism of delegation 23 Figure 3-2 A more realistic sequence involving a delegate 23 Listing 3-1 Sample delegation methods with return values 24 Listing 3-2 Sample delegation methods returning void 24 Introspection 29 Listing 4-1 Using the class and superclass methods 29 Listing 4-2 Using isKindOfClass: 30 Listing 4-3 Using respondsToSelector: 31 Listing 4-4 Using conformsToProtocol: 31 Listing 4-5 Using isEqual: 32 Listing 4-6 Overriding isEqual: 32 Object Initialization 35 Figure 6-1 Initialization up the inheritance chain 39 Figure 6-2 Interactions of secondary and designated initializers 41 Model-View-Controller 43 Figure 7-1 Traditional version of MVC as a compound pattern 48 Figure 7-2 Cocoa version of MVC as a compound design pattern 48 Figure 7-3 Coordinating controller as the owner of a nib file 50 Object Modeling 53 Figure 8-1 Employee management application object diagram 54 Figure 8-2 Employees table view 55 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 5Figure 8-3 Relationships in the employee management application 56 Figure 8-4 Relationship cardinality 56 Figure 8-5 Object graph for the employee management application 58 Figure 8-6 Employees table view showing department name 59 Object Mutability 60 Listing 9-1 Returning an immutable copy of a mutable instance variable 63 Listing 9-2 Making a snapshot of a potentially mutable object 65 Receptionist Pattern 68 Figure 11-1 Bouncing KVO updates to the main operation queue 69 Listing 11-1 Declaring the receptionist class 69 Listing 11-2 The class factory method for creating a receptionist object 70 Listing 11-3 Handling the KVO notification 71 Listing 11-4 Creating a receptionist object 71 Target-Action 73 Figure 12-1 How the target-action mechanism works in the control-cell architecture 76 Toll-Free Bridging 80 Table 13-1 Data types that can be used interchangeably between Core Foundation and Foundation 81 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 6 Figures, Tables, and ListingsMany of the programmatic interfaces of the Cocoa and Cocoa Touch frameworks only make sense only if you are aware of the concepts on which they are based. These concepts express the rationale for many of the core designs of the frameworks. Knowledge of these concepts will illuminate your software-development practices. Model layer View layer Controller layer Application delegate System frameworks At a Glance This document contains articles that explain central concepts, design patterns, and mechanisms of the Cocoa and Cocoa Touch frameworks. The articles are arranged in alphabetical order. How to Use This Document If you read this document cover-to-cover, you learn important information about Cocoa and Cocoa Touch application development. However, most readers come to the articles in this document in one of two ways: ● Other documents—especially those that are intended for novice iOS and OS X developers—which link to these articles. ● In-line mini-articles (which appear when you click a dash-underlined word or phrase) that have a link to an article as a “Definitive Discussion.” 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 7 About the Basic Programming Concepts for Cocoa and Cocoa TouchPrerequisites Prior programming experience, especially with object-oriented languages, is recommended. See Also The Objective-C Programming Language offers further discussion of many of the language-related concepts covered in this document. About the Basic Programming Concepts for Cocoa and Cocoa Touch Prerequisites 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 8Class clusters are a design pattern that the Foundation framework makes extensive use of. Class clusters group a number of private concrete subclasses under a public abstract superclass. The grouping of classes in this way simplifies the publicly visible architecture of an object-oriented framework without reducing its functional richness. Class clusters are based on the Abstract Factory design pattern. Without Class Clusters: Simple Concept but Complex Interface To illustrate the class cluster architecture and its benefits, consider the problem of constructing a class hierarchy that defines objects to store numbers of different types (char, int, float, double). Because numbers of different types have many features in common (they can be converted from one type to another and can be represented as strings, for example), they could be represented by a single class. However, their storage requirements differ,so it’sinefficient to represent them all by the same class. Taking thisfact into consideration, one could design the class architecture depicted in Figure 1-1 to solve the problem. Figure 1-1 A simple hierarchy for number classes Number is the abstract superclass that declares in its methods the operations common to its subclasses. However, it doesn’t declare an instance variable to store a number. The subclasses declare such instance variables and share in the programmatic interface declared by Number. 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 9 Class ClustersSo far, this design is relatively simple. However, if the commonly used modifications of these basic C types are taken into account, the class hierarchy diagram looks more like Figure 1-2. Figure 1-2 A more complete number class hierarchy The simple concept—creating a class to hold number values—can easily burgeon to over a dozen classes. The class cluster architecture presents a design that reflects the simplicity of the concept. With Class Clusters: Simple Concept and Simple Interface Applying the class cluster design pattern to this problem yieldsthe class hierarchy in Figure 1-3 (private classes are in gray). Figure 1-3 Class cluster architecture applied to number classes Users of this hierarchy see only one public class, Number, so how is it possible to allocate instances of the proper subclass? The answer is in the way the abstract superclass handles instantiation. Creating Instances The abstract superclass in a class cluster must declare methods for creating instances of its private subclasses. It’s the superclass’s responsibility to dispense an object of the proper subclass based on the creation method that you invoke—you don’t, and can’t, choose the class of the instance. In the Foundation framework, you generally create an object by invoking a +className... method or the alloc... and init... methods. Taking the Foundation framework’s NSNumber class as an example, you could send these messages to create number objects: Class Clusters With Class Clusters: Simple Concept and Simple Interface 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 10NSNumber *aChar = [NSNumber numberWithChar:’a’]; NSNumber *anInt = [NSNumber numberWithInt:1]; NSNumber *aFloat = [NSNumber numberWithFloat:1.0]; NSNumber *aDouble = [NSNumber numberWithDouble:1.0]; You are not responsible for releasing the objects returned from factory methods. Many classes also provide the standard alloc... and init... methodsto create objectsthat require you to manage their deallocation. Each object returned—aChar, anInt, aFloat, and aDouble—may belong to a different private subclass (and in fact does). Although each object’s class membership is hidden, itsinterface is public, being the interface declared by the abstract superclass, NSNumber. Although it is not precisely correct, it’s convenient to consider the aChar, anInt, aFloat, and aDouble objects to be instances of the NSNumber class, because they’re created by NSNumber class methods and accessed through instance methods declared by NSNumber. Class Clusters with Multiple Public Superclasses In the example above, one abstract public class declares the interface for multiple private subclasses. This is a class cluster in the purest sense. It’s also possible, and often desirable, to have two (or possibly more) abstract public classes that declare the interface for the cluster. This is evident in the Foundation framework, which includes the clusters listed in Table 1-1. Table 1-1 Class clusters and their public superclasses Class cluster Public superclasses NSData NSData NSMutableData NSArray NSArray NSMutableArray NSDictionary NSDictionary NSMutableDictionary NSString NSString NSMutableString Class Clusters Class Clusters with Multiple Public Superclasses 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 11Other clusters of this type also exist, but these clearly illustrate how two abstract nodes cooperate in declaring the programmatic interface to a class cluster. In each of these clusters, one public node declares methods that all cluster objects can respond to, and the other node declares methods that are only appropriate for cluster objects that allow their contents to be modified. This factoring of the cluster’s interface helps make an object-oriented framework’s programmatic interface more expressive. For example, imagine an object representing a book that declares this method: - (NSString *)title; The book object could return its own instance variable or create a new string object and return that—it doesn’t matter. It’s clear from this declaration that the returned string can’t be modified. Any attempt to modify the returned object will elicit a compiler warning. Creating Subclasses Within a Class Cluster The class cluster architecture involves a trade-off between simplicity and extensibility: Having a few public classes stand in for a multitude of private ones makes it easier to learn and use the classes in a framework but somewhat harder to create subclasses within any of the clusters. However, if it’s rarely necessary to create a subclass, then the cluster architecture is clearly beneficial. Clusters are used in the Foundation framework in just these situations. If you find that a cluster doesn’t provide the functionality your program needs, then a subclass may be in order. For example, imagine that you want to create an array object whose storage is file-based rather than memory-based, as in the NSArray class cluster. Because you are changing the underlying storage mechanism of the class, you’d have to create a subclass. On the other hand, in some cases it might be sufficient (and easier) to define a class that embeds within it an object from the cluster. Let’s say that your program needs to be alerted whenever some data is modified. In this case, creating a simple class that wraps a data object that the Foundation framework defines may be the best approach. An object of this class could intervene in messages that modify the data, intercepting the messages, acting on them, and then forwarding them to the embedded data object. In summary, if you need to manage your object’sstorage, create a true subclass. Otherwise, create a composite object, one that embeds a standard Foundation framework object in an object of your own design. The following sections give more detail on these two approaches. A True Subclass A new class that you create within a class cluster must: Class Clusters Creating Subclasses Within a Class Cluster 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 12● Be a subclass of the cluster’s abstract superclass ● Declare its own storage ● Override all initializer methods of the superclass ● Override the superclass’s primitive methods (described below) Because the cluster’s abstract superclass is the only publicly visible node in the cluster’s hierarchy, the first point is obvious. This implies that the new subclass will inherit the cluster’s interface but no instance variables, because the abstract superclass declares none. Thus the second point: The subclass must declare any instance variables it needs. Finally, the subclass must override any method it inherits that directly accesses an object’s instance variables. Such methods are called primitive methods. A class’s primitive methodsform the basisfor itsinterface. For example, take the NSArray class, which declares the interface to objects that manage arrays of objects. In concept, an array stores a number of data items, each of which is accessible by index. NSArray expresses this abstract notion through its two primitive methods, count and objectAtIndex:. With these methods as a base, other methods—derived methods—can be implemented; Table 1-2 gives two examples of derived methods. Table 1-2 Derived methods and their possible implementations Derived Method Possible Implementation Find the last object by sending the array object this message: [self objectAtIndex: ([self count] –1)]. lastObject Find an object by repeatedly sending the array object an objectAtIndex: message, each time incrementing the index until all objects in the array have been tested. containsObject: The division of an interface between primitive and derived methods makes creating subclasses easier. Your subclass must override inherited primitives, but having done so can be sure that all derived methods that it inherits will operate properly. The primitive-derived distinction applies to the interface of a fully initialized object. The question of how init... methods should be handled in a subclass also needs to be addressed. In general, a cluster’s abstract superclass declares a number of init... and + className methods. As described in “Creating Instances” (page 10), the abstract class decides which concrete subclass to instantiate based your choice of init... or + className method. You can consider that the abstract class declares these methods for the convenience of the subclass. Since the abstract class has no instance variables, it has no need of initialization methods. Class Clusters Creating Subclasses Within a Class Cluster 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 13Your subclass should declare its own init... (if it needs to initialize its instance variables) and possibly + className methods. It should not rely on any of those that it inherits. To maintain its link in the initialization chain, it should invoke its superclass’s designated initializer within its own designated initializer method. It should also override all other inherited initializer methods and implement them to behave in a reasonable manner. (See ““The Runtime System”“ in The Objective-C Programming Language for a discussion of designated initializers.) Within a class cluster, the designated initializer of the abstract superclass is always init. True Subclasses: An Example Let’s say that you want to create a subclass of NSArray, named MonthArray, that returns the name of a month given its index position. However, a MonthArray object won’t actually store the array of month names as an instance variable. Instead, the method that returns a name given an index position (objectAtIndex:) will return constantstrings. Thus, only twelve string objects will be allocated, no matter how many MonthArray objects exist in an application. The MonthArray class is declared as: #import @interface MonthArray : NSArray { } + monthArray; - (unsigned)count; - (id)objectAtIndex:(unsigned)index; @end Note that the MonthArray class doesn’t declare an init... method because it has no instance variables to initialize. The count and objectAtIndex: methodssimply cover the inherited primitive methods, as described above. The implementation of the MonthArray class looks like this: #import "MonthArray.h" @implementation MonthArray Class Clusters Creating Subclasses Within a Class Cluster 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 14static MonthArray *sharedMonthArray = nil; static NSString *months[] = { @"January", @"February", @"March", @"April", @"May", @"June", @"July", @"August", @"September", @"October", @"November", @"December" }; + monthArray { if (!sharedMonthArray) { sharedMonthArray = [[MonthArray alloc] init]; } return sharedMonthArray; } - (unsigned)count { return 12; } - objectAtIndex:(unsigned)index { if (index >= [self count]) [NSException raise:NSRangeException format:@"***%s: index (%d) beyond bounds (%d)", sel_getName(_cmd), index, [self count] - 1]; else return months[index]; } @end Because MonthArray overridesthe inherited primitive methods, the derived methodsthat it inherits will work properly without being overridden. NSArray’s lastObject, containsObject:, sortedArrayUsingSelector:, objectEnumerator, and other methods work without problems for MonthArray objects. Class Clusters Creating Subclasses Within a Class Cluster 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 15A Composite Object By embedding a private cluster object in an object of your own design, you create a composite object. This composite object can rely on the cluster object for its basic functionality, only intercepting messages that the composite object wants to handle in some particular way. This architecture reduces the amount of code you must write and lets you take advantage of the tested code provided by the Foundation Framework. Figure 1-4 depicts this architecture. Figure 1-4 An object that embeds a cluster object The composite object must declare itself to be a subclass of the cluster’s abstract superclass. As a subclass, it must override the superclass’s primitive methods. It can also override derived methods, but this isn’t necessary because the derived methods work through the primitive ones. The count method of the NSArray class is an example; the intervening object’s implementation of a method it overrides can be as simple as: - (unsigned)count { return [embeddedObject count]; } However, your object could put code for its own purposes in the implementation of any method it overrides. A Composite Object: An Example To illustrate the use of a composite object, imagine you want a mutable array object that tests changes against some validation criteria before allowing any modification to the array’s contents. The example that follows describes a class called ValidatingArray, which contains a standardmutable array object. ValidatingArray overrides all of the primitive methods declared in its superclasses, NSArray and NSMutableArray. It also declares the array, validatingArray, and init methods, which can be used to create and initialize an instance: #import Class Clusters Creating Subclasses Within a Class Cluster 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 16@interface ValidatingArray : NSMutableArray { NSMutableArray *embeddedArray; } + validatingArray; - init; - (unsigned)count; - objectAtIndex:(unsigned)index; - (void)addObject:object; - (void)replaceObjectAtIndex:(unsigned)index withObject:object; - (void)removeLastObject; - (void)insertObject:object atIndex:(unsigned)index; - (void)removeObjectAtIndex:(unsigned)index; @end The implementation file shows how, in an init method of the ValidatingArrayclass, the embedded object is created and assigned to the embeddedArray variable. Messages that simply access the array but don’t modify its contents are relayed to the embedded object. Messagesthat could change the contents are scrutinized (here in pseudocode) and relayed only if they pass the hypothetical validation test. #import "ValidatingArray.h" @implementation ValidatingArray - init { self = [super init]; if (self) { embeddedArray = [[NSMutableArray allocWithZone:[self zone]] init]; } return self; } Class Clusters Creating Subclasses Within a Class Cluster 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 17+ validatingArray { return [[[self alloc] init] autorelease]; } - (unsigned)count { return [embeddedArray count]; } - objectAtIndex:(unsigned)index { return [embeddedArray objectAtIndex:index]; } - (void)addObject:object { if (/* modification is valid */) { [embeddedArray addObject:object]; } } - (void)replaceObjectAtIndex:(unsigned)index withObject:object; { if (/* modification is valid */) { [embeddedArray replaceObjectAtIndex:index withObject:object]; } } - (void)removeLastObject; { if (/* modification is valid */) { [embeddedArray removeLastObject]; Class Clusters Creating Subclasses Within a Class Cluster 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 18} } - (void)insertObject:object atIndex:(unsigned)index; { if (/* modification is valid */) { [embeddedArray insertObject:object atIndex:index]; } } - (void)removeObjectAtIndex:(unsigned)index; { if (/* modification is valid */) { [embeddedArray removeObjectAtIndex:index]; } } Class Clusters Creating Subclasses Within a Class Cluster 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 19Class factory methods are implemented by a class as a convenience for clients. They combine allocation and initialization in one step and return the created object. However, the client receiving this object does not own the object and thus (per the object-ownership policy) is not responsible for releasing it. These methods are of the form + (type)className... (where className excludes any prefix). Cocoa provides plenty of examples, especially among the “value” classes. NSDate includes the following class factory methods: + (id)dateWithTimeIntervalSinceNow:(NSTimeInterval)secs; + (id)dateWithTimeIntervalSinceReferenceDate:(NSTimeInterval)secs; + (id)dateWithTimeIntervalSince1970:(NSTimeInterval)secs; And NSData offers the following factory methods: + (id)dataWithBytes:(const void *)bytes length:(unsigned)length; + (id)dataWithBytesNoCopy:(void *)bytes length:(unsigned)length; + (id)dataWithBytesNoCopy:(void *)bytes length:(unsigned)length freeWhenDone:(BOOL)b; + (id)dataWithContentsOfFile:(NSString *)path; + (id)dataWithContentsOfURL:(NSURL *)url; + (id)dataWithContentsOfMappedFile:(NSString *)path; Factory methods can be more than a simple convenience. They can not only combine allocation and initialization, but the allocation can inform the initialization. As an example, let’s say you must initialize a collection object from a property-list file that encodes any number of elements for the collection (NSString objects, NSData objects, NSNumber objects, and so on). Before the factory method can know how much memory to allocate for the collection, it must read the file and parse the property list to determine how many elements there are and what object type these elements are. 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 20 Class Factory MethodsAnother purpose for a classfactory method isto ensure that a certain class(NSWorkspace, for example) vends a singleton instance. Although an init... method could verify that only one instance exists at any one time in a program, it would require the prior allocation of a “raw” instance and then, in memory-managed code, would have to release that instance. A factory method, on the other hand, gives you a way to avoid blindly allocating memory for an object that you might not use, as in the following example: static AccountManager *DefaultManager = nil; + (AccountManager *)defaultManager { if (!DefaultManager) DefaultManager = [[self allocWithZone:NULL] init]; return DefaultManager; } Class Factory Methods 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 21A delegate is an object that acts on behalf of, or in coordination with, another object when that object encounters an event in a program. The delegating object is often a responder object—that is, an object inheriting from NSResponder in AppKit or UIResponder in UIKit—that is responding to a user event. The delegate is an object that is delegated control of the user interface for that event, or is at least asked to interpret the event in an application-specific manner. To better appreciate the value of delegation, it helps to consider an off-the-shelf Cocoa object such as a text field (an instance of NSTextField or UITextField) or a table view (an instance of NSTableView or UITableView ). These objects are designed to fulfill a specific role in a generic fashion; a window object in the AppKit framework, for example, responds to mouse manipulations of its controls and handles such things as closing, resizing, and moving the physical window. This restricted and generic behavior necessarily limits what the object can know about how an event affects (or will affect) something elsewhere in the application, especially when the affected behavior isspecific to your application. Delegation provides a way for your custom object to communicate application-specific behavior to the off-the-shelf object. The programming mechanism of delegation gives objects a chance to coordinate their appearance and state with changes occurring elsewhere in a program, changes usually brought about by user actions. More importantly, delegation makes it possible for one object to alter the behavior of another object without the need to inherit from it. The delegate is almost always one of your custom objects, and by definition it incorporates application-specific logic that the generic and delegating object cannot possibly know itself. How Delegation Works The design of the delegation mechanism is simple—see Figure 3-1 (page 23). The delegating class has an outlet or property, usually one that is named delegate; if it is an outlet, it includes methods for setting and accessing the value of the outlet. It also declares, without implementing, one or more methods that constitute a formal protocol or an informal protocol. A formal protocol that uses optional methods—a feature ofObjective-C 2.0—is the preferred approach, but both kinds of protocols are used by the Cocoa frameworks for delegation. In the informal protocol approach, the delegating class declares methods on a category of NSObject, and the delegate implements only those methods in which it has an interest in coordinating itself with the delegating object or affecting that object’s default behavior. If the delegating class declares a formal protocol, the delegate may choose to implement those methods marked optional, but it must implement the required ones. 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 22 Delegates and Data SourcesDelegation follows a common design, illustrated by Figure 3-1. Figure 3-1 The mechanism of delegation User just clicked close button; should window close? No windowShouldClose: Don't close. The window has unsaved data. windowDelegate The methods of the protocol mark significant events handled or anticipated by the delegating object. This object wants either to communicate these events to the delegate or, for impending events, to request input or approval from the delegate. For example, when a user clicks the close button of a window in OS X, the window object sends the windowShouldClose: message to its delegate; this gives the delegate the opportunity to veto or defer the closing of the window if, for example, the window has associated data that must be saved (see Figure 3-2). Figure 3-2 A more realistic sequence involving a delegate Yes windowShouldClose: ➌ ➊ ➍ ➋ aWindow aDelegate The delegating object sends a message only if the delegate implements the method. It makes this discovery by invoking the NSObjectmethod respondsToSelector: in the delegate first. Delegates and Data Sources How Delegation Works 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 23The Form of Delegation Messages Delegation methods have a conventional form. They begin with the name of the AppKit or UIKit object doing the delegating—application, window, control, and so on; this name is in lower-case and without the “NS” or “UI” prefix. Usually (but not always) this object name is followed by an auxiliary verb indicative of the temporal status of the reported event. This verb, in other words, indicates whether the event is about to occur (“Should” or “Will”) or whether it has just occurred (“Did” or “Has”). This temporal distinction helps to categorize those messagesthat expect a return value and those that don’t. Listing 3-1 includes a few AppKit delegation methods that expect a return value. Listing 3-1 Sample delegation methods with return values - (BOOL)application:(NSApplication *)sender openFile:(NSString *)filename; // NSApplication - (BOOL)application:(UIApplication *)application handleOpenURL:(NSURL *)url; // UIApplicationDelegate - (UITableRowIndexSet *)tableView:(NSTableView *)tableView willSelectRows:(UITableRowIndexSet *)selection; // UITableViewDelegate - (NSRect)windowWillUseStandardFrame:(NSWindow *)window defaultFrame:(NSRect)newFrame; // NSWindow The delegate that implements these methods can block the impending event (by returning NO in the first two methods) or alter a suggested value (the index set and the frame rectangle in the last two methods). It can even defer an impending event; for example, the delegate implementing the applicationShouldTerminate:method can delay application termination by returning NSTerminateLater. Other delegation methods are invoked by messagesthat don’t expect a return value and so are typed to return void. These messages are purely informational, and the method names often contain “Did”, “Will”, or some other indication of a transpired or impending event. Listing 3-2 shows a few examples of these kinds of delegation method. Listing 3-2 Sample delegation methods returning void - (void) tableView:(NSTableView*)tableView mouseDownInHeaderOfTableColumn:(NSTableColumn *)tableColumn; // NSTableView - (void)windowDidMove:(NSNotification *)notification; // NSWindow - (void)application:(UIApplication *)application willChangeStatusBarFrame:(CGRect)newStatusBarFrame; // UIApplication Delegates and Data Sources The Form of Delegation Messages 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 24- (void)applicationWillBecomeActive:(NSNotification *)notification; // NSApplication There are a couple of things to note about this last group of methods. The first is that an auxiliary verb of “Will” (as in the third method) does not necessarily mean that a return value is expected. In this case, the event is imminent and cannot be blocked, but the message gives the delegate an opportunity to prepare the program for the event. The other point of interest concernsthe second and last method declarationsin Listing 3-2 . The sole parameter of each of these methods is an NSNotification object, which means that these methods are invoked as the result of the posting of a particular notification. For example, the windowDidMove: method is associated with the NSWindow notification NSWindowDidMoveNotification. It’s important to understand the relationship of notifications to delegation messages in AppKit. The delegating object automatically makes its delegate an observer of all notifications it posts. All the delegate needs to do is implement the associated method to get the notification. To make an instance of your custom class the delegate of an AppKit object, simply connect the instance to the delegate outlet or property in Interface Builder. Or you can set it programmatically through the delegating object’s setDelegate: method or delegate property, preferably early on, such as in the awakeFromNib or applicationDidFinishLaunching: method. Delegation and the Application Frameworks The delegating object in a Cocoa or Cocoa Touch application is often a responder object such as a UIApplication, NSWindow, or NSTableView object. The delegate object itself istypically, but not necessarily, an object, often a custom object, that controls some part of the application (that is, a coordinating controller object). The following AppKit classes define a delegate: ● NSApplication ● NSBrowser ● NSControl ● NSDrawer ● NSFontManager ● NSFontPanel ● NSMatrix ● NSOutlineView ● NSSplitView Delegates and Data Sources Delegation and the Application Frameworks 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 25● NSTableView ● NSTabView ● NSText ● NSTextField ● NSTextView ● NSWindow The UIKit framework also uses delegation extensively and always implements it using formal protocols. The application delegate is extremely important in an application running in iOS because it must respond to application-launch, application-quit, low-memory, and other messages from the application object. The application delegate must adopt the UIApplicationDelegate protocol. Delegating objects do not (and should not) retain their delegates. However, clients of delegating objects (applications, usually) are responsible for ensuring that their delegates are around to receive delegation messages. To do this, they may have to retain the delegate in memory-managed code. This precaution applies equally to data sources, notification observers, and targets of action messages. Note that in a garbage-collection environment, the reference to the delegate is strong because the retain-cycle problem does not apply. Some AppKit classes have a more restricted type of delegate called a modal delegate . Objects of these classes (NSOpenPanel, for example) run modal dialogs that invoke a handler method in the designated delegate when the user clicksthe dialog’s OK button. Modal delegates are limited in scope to the operation of the modal dialog. Becoming the Delegate of a Framework Class A framework class or any other classthat implements delegation declares a delegate property and a protocol (usually a formal protocol). The protocol liststhe required and optional methodsthat the delegate implements. For an instance of your class to function as the delegate of a framework object, it must do the following: ● Set your object asthe delegate (by assigning it to the delegate property). You can do this programmatically or through Interface Builder. ● If the protocol is formal, declare that your class adopts the protocol in the class definition. For example: @interface MyControllerClass : UIViewController { ● Implement all required methods of the protocol and any optional methods that you want to participate in. Delegates and Data Sources Delegation and the Application Frameworks 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 26Locating Objects Through the delegate Property The existence of delegates has other programmatic uses. For example, with delegates it is easy for two coordinating controllers in the same program to find and communicate with each other. For example, the object controlling the application overall can find the controller of the application’sinspector window (assuming it’s the current key window) using code similar to the following: id winController = [[NSApp keyWindow] delegate]; And your code can find the application-controller object—by definition, the delegate of the global application instance—by doing something similar to the following: id appController = [NSApp delegate]; Data Sources A data source is like a delegate except that, instead of being delegated control of the user interface, it is delegated control of data. A data source is an outlet held by NSView and UIView objects such as table views and outline views that require a source from which to populate their rows of visible data. The data source for a view is usually the same object that acts as its delegate, but it can be any object. As with the delegate, the data source must implement one or more methods of an informal protocol to supply the view with the data it needs and, in more advanced implementations, to handle data that users directly edit in such views. As with delegates, data sources are objectsthat must be present to receive messagesfrom the objectsrequesting data. The application that uses them must ensure their persistence, retaining them if necessary in memory-managed code. Data sources are responsible for the persistence of the objectsthey hand out to user-interface objects. In other words, they are responsible for the memory management of those objects. However, whenever a view object such as an outline view or table view accesses the data from a data source, it retains the objects as long as it uses the data. But it does not use the data for very long. Typically it holds on to the data only long enough to display it. Implementing a Delegate for a Custom Class To implement a delegate for your custom class, complete the following steps: ● Declare the delegate accessor methods in your class header file. Delegates and Data Sources Data Sources 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 27- (id)delegate; - (void)setDelegate:(id)newDelegate; ● Implement the accessor methods. In a memory-managed program, to avoid retain cycles, the setter method should not retain or copy your delegate. - (id)delegate { return delegate; } - (void)setDelegate:(id)newDelegate { delegate = newDelegate; } In a garbage-collected environment, where retain cycles are not a problem, you should not make the delegate a weak reference (by using the __weak type modifier). For more on retain cycles, see Advanced MemoryManagement ProgrammingGuide . Formore on weak referencesin garbage collection,see “Garbage Collection for Cocoa Essentials” in Garbage Collection Programming Guide . ● Declare a formal or informal protocol containing the programmatic interface for the delegate. Informal protocols are categories on the NSObject class. If you declare a formal protocol for your delegate, make sure you mark groups of optional methods with the @optional directive. “The Form of Delegation Messages” (page 24) gives advice for naming your own delegation methods. ● Before invoking a delegation method, make sure the delegate implements it by sending it a respondsToSelector: message. - (void)someMethod { if ( [delegate respondsToSelector:@selector(operationShouldProceed)] ) { if ( [delegate operationShouldProceed] ) { // do something appropriate } } } The precaution is necessary only for optional methods in a formal protocol or methods of an informal protocol. Delegates and Data Sources Implementing a Delegate for a Custom Class 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 28Introspection is a powerful feature of object-oriented languages and environments, and introspection in Objective-C and Cocoa is no exception. Introspection refersto the capability of objectsto divulge details about themselves as objects at runtime. Such details include an object’s place in the inheritance tree, whether it conforms to a specific protocol, and whether it responds to a certain message. The NSObject protocol and class define many introspection methodsthat you can use to query the runtime in order to characterize objects. Used judiciously, introspection makes an object-oriented program more efficient and robust. It can help you avoid message-dispatch errors, erroneous assumptions of object equality, and similar problems. The following sections show how you might effectively use the NSObject introspection methods in your code. Evaluating Inheritance Relationships Once you know the class an object belongs to, you probably know quite a bit about the object. You might know what its capabilities are, what attributes it represents, and what kinds of messages it can respond to. Even if after introspection you are unfamiliar with the classto which an object belongs, you now know enough to not send it certain messages. The NSObject protocol declares several methods for determining an object’s position in the class hierarchy. These methods operate at different granularities. The class and superclass instance methods, for example, return the Class objects representing the class and superclass, respectively, of the receiver. These methods require you to compare one Class object with another. Listing 4-1 gives a simple (one might say trivial) example of their use. Listing 4-1 Using the class and superclass methods // ... while ( id anObject = [objectEnumerator nextObject] ) { if ( [self class] == [anObject superclass] ) { // do something appropriate... } } 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 29 IntrospectionNote: Sometimes you use the class or superclass methods to obtain an appropriate receiver for a class message. More commonly, to check an object’s class affiliation, you would send it a isKindOfClass: or isMemberOfClass: message. The former method returns whether the receiver is an instance of a given class or an instance of any class that inherits from that class. A isMemberOfClass: message, on the other hand, tells you if the receiver is an instance of the specified class. The isKindOfClass: method is generally more useful because from it you can know at once the complete range of messages you can send to an object. Consider the code snippet in Listing 4-2. Listing 4-2 Using isKindOfClass: if ([item isKindOfClass:[NSData class]]) { const unsigned char *bytes = [item bytes]; unsigned int length = [item length]; // ... } By learning that the object item inheritsfrom the NSData class, this code knowsit can send it the NSDatabytes and lengthmessages. The difference between isKindOfClass: and isMemberOfClass: becomes apparent if you assume that item is an instance of NSMutableData. If you use isMemberOfClass: instead of isKindOfClass:, the code in the conditionalized block is never executed because item is not an instance of NSData but rather of NSMutableData, a subclass of NSData. Method Implementation and Protocol Conformance Two of the more powerful introspection methods of NSObject are respondsToSelector: and conformsToProtocol:. These methodstell you, respectively, whether an object implements a certain method and whether an object conforms to a specified formal protocol (that is, adopts the protocol, if necessary, and implements all the methods of the protocol). You use these methodsin a similarsituation in your code. They enable you to discover whethersome potentially anonymous object can respond appropriately to a particular message or set of messages before you send it any of those messages. By making this check before sending a message, you can avoid the risk of runtime exceptionsresulting from unrecognized selectors. The AppKit framework implementsinformal protocols—the basis of delegation—by checking whether delegates implement a delegation method (using respondsToSelector:) prior to invoking that method. Introspection Method Implementation and Protocol Conformance 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 30Listing 4-3 illustrates how you might use the respondsToSelector: method in your code. Listing 4-3 Using respondsToSelector: - (void)doCommandBySelector:(SEL)aSelector { if ([self respondsToSelector:aSelector]) { [self performSelector:aSelector withObject:nil]; } else { [_client doCommandBySelector:aSelector]; } } Listing 4-4 illustrates how you might use the conformsToProtocol: method in your code. Listing 4-4 Using conformsToProtocol: // ... if (!([((id)testObject) conformsToProtocol:@protocol(NSMenuItem)])) { NSLog(@"Custom MenuItem, '%@', not loaded; it must conform to the 'NSMenuItem' protocol.\n", [testObject class]); [testObject release]; testObject = nil; } Object Comparison Although they are not strictly introspection methods, the hash and isEqual: methods fulfill a similar role. They are indispensable runtime toolsfor identifying and comparing objects. But instead of querying the runtime for information about an object, they rely on class-specific comparison logic. The hash and isEqual: methods, both declared by the NSObject protocol, are closely related. The hash method must be implemented to return an integer that can be used as a table addressin a hash table structure. If two objects are equal (as determined by the isEqual: method), they must have the same hash value. If your object could be included in collections such as NSSet objects, you need to define hash and verify the invariant that if two objects are equal, they return the same hash value. The default NSObject implementation of isEqual: simply checks for pointer equality. Introspection Object Comparison 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 31Using the isEqual: method is straightforward; it compares the receiver against the object supplied as a parameter. Object comparison frequently informsruntime decisions about whatshould be done with an object. As Listing 4-5 illustrates, you can use isEqual: to decide whether to perform an action, in this case to save user preferences that have been modified. Listing 4-5 Using isEqual: - (void)saveDefaults { NSDictionary *prefs = [self preferences]; if (![origValues isEqual:prefs]) [Preferences savePreferencesToDefaults:prefs]; } If you are creating a subclass, you might need to override isEqual: to add further checksfor points of equality. The subclass might define an extra attribute that has to be the same value in two instances for them to be considered equal. For example, say you create a subclass of NSObject called MyWidget that contains two instance variables, name and data. Both of these must be the same value for two instances of MyWidget to be considered equal. Listing 4-6 illustrates how you might implement isEqual: for the MyWidget class. Listing 4-6 Overriding isEqual: - (BOOL)isEqual:(id)other { if (other == self) return YES; if (!other || ![other isKindOfClass:[self class]]) return NO; return [self isEqualToWidget:other]; } - (BOOL)isEqualToWidget:(MyWidget *)aWidget { if (self == aWidget) return YES; if (![(id)[self name] isEqual:[aWidget name]]) return NO; if (![[self data] isEqualToData:[aWidget data]]) return NO; return YES; Introspection Object Comparison 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 32} This isEqual: method first checks for pointer equality, then class equality, and finally invokes an object comparator whose name indicates the class of object involved in the comparison. This type of comparator, which forcestype checking of the object passed in, is a common convention in Cocoa; the isEqualToString: method of the NSString class and the isEqualToTimeZone: method of the NSTimeZone class are but two examples. The class-specific comparator—isEqualToWidget: in this case—performs the checks for name and data equality. In all isEqualToType: methods of the Cocoa frameworks, nil is not a valid parameter and implementations of these methods may raise an exception upon receiving a nil. However, for backward compatibility, isEqual: methods of the Cocoa frameworks do accept nil, returning NO. Introspection Object Comparison 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 33When you allocate an object, part of what happens is what you might expect, given the term. Cocoa allocates enough memory for the object from a region of application virtual memory. To calculate how much memory to allocate, it takes the object’s instance variables into account—including their types and order—as specified by the object’s class. To allocate an object, you send the message alloc or allocWithZone: to the object’s class. In return, you get a “raw” (uninitialized) instance of the class. The alloc variant of the method uses the application’s default zone. A zone is a page-aligned area of memory for holding related objects and data allocated by an application. See Advanced Memory Management Programming Guide for more information on zones. An allocation message does other important things besides allocating memory: ● It sets the object’s retain count to one. ● It initializes the object’s isainstance variable to point to the object’s class, a runtime object in its own right that is compiled from the class definition. ● It initializes all other instance variables to zero (or to the equivalent type for zero, such as nil, NULL, and 0.0). An object’s isa instance variable is inherited from NSObject, so it is common to all Cocoa objects. After allocation sets isa to the object’s class, the object is integrated into the runtime’s view of the inheritance hierarchy and the current network of objects (class and instance) that constitute a program. Consequently an object can find whatever information it needs at runtime, such as another object’s place in the inheritance hierarchy, the protocols that other objects conform to, and the location of the method implementations it can perform in response to messages. In summary, allocation not only allocates memory for an object but initializes two small but very important attributes of any object: its isa instance variable and itsretain count. It also sets all remaining instance variables to zero. But the resulting object is not yet usable. Initializing methods such as init must yet initialize objects with their particular characteristics and return a functional object. 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 34 Object AllocationInitialization sets the instance variables of an object to reasonable and useful initial values. It can also allocate and prepare other global resources needed by the object, loading them if necessary from an external source such as a file. Every object that declares instance variables should implement an initializing method—unless the defaultset-everything-to-zero initialization issufficient. If an object does not implement an initializer, Cocoa invokes the initializer of the nearest ancestor instead. The Form of Initializers NSObject declares the init prototype for initializers; it is an instance method typed to return an object of type id. Overriding init is fine for subclasses that require no additional data to initialize their objects. But often initialization depends on external data to set an object to a reasonable initial state. For example, say you have an Account class; to initialize an Account object appropriately requires a unique account number, and this must be supplied to the initializer. Thus initializers can take one or more parameters; the only requirement is that the initializing method begins with the letters “init”. (The stylistic convention init... is sometimes used to refer to initializers.) Note: Instead of implementing an initializer with parameters, a subclass can implement only a simple init method and then use “set” accessor methods immediately after initialization to set the object to a useful initial state. (Accessor methods enforce encapsulation of object data by setting and getting the values of instance variables.) Or, if the subclass uses properties and the related access syntax, it may assign values to the properties immediately after initialization. Cocoa has plenty of examples of initializers with parameters. Here are a few (with the defining class in parentheses): - (id)initWithArray:(NSArray *)array; (from NSSet) - (id)initWithTimeInterval:(NSTimeInterval)secsToBeAdded sinceDate:(NSDate *)anotherDate; (from NSDate) - (id)initWithContentRect:(NSRect)contentRect styleMask:(unsigned int)aStyle backing:(NSBackingStoreType)bufferingType defer:(BOOL)flag; (from NSWindow) - (id)initWithFrame:(NSRect)frameRect; (from NSControl and NSView) 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 35 Object InitializationThese initializers are instance methods that begin with “init” and return an object of the dynamic type id. Other than that, they follow the Cocoa conventions for multiparameter methods, often using WithType: or FromSource: before the first and most important parameter. Issues with Initializers Although init... methods are required by their method signature to return an object, that object is not necessarily the one that was most recently allocated—the receiver of the init... message. In other words, the object you get back from an initializer might not be the one you thought was being initialized. Two conditions prompt the return of something other than the just-allocated object. The first involves two related situations: when there must be a singleton instance or when the defining attribute of an object must be unique. Some Cocoa classes—NSWorkspace, for instance—allow only one instance in a program; a class in such a case must ensure (in an initializer or, more likely, in a class factory method) that only one instance is created, returning this instance if there is any further request for a new one. A similar situation arises when an object is required to have an attribute that makes it unique. Recall the hypothetical Account class mentioned earlier. An account of any sort must have a unique identifier. If the initializer for this class—say, initWithAccountID:—is passed an identifier that has already been associated with an object, it must do two things: ● Release the newly allocated object (in memory-managed code) ● Return the Account object previously initialized with this unique identifier By doing this, the initializer ensures the uniqueness of the identifier while providing what was asked for: an Account instance with the requested identifier. Sometimes an init... method cannot perform the initialization requested. For example, an initFromFile: method expects to initialize an object from the contents of a file, the path to which is passed as a parameter. But if no file exists at that location, the object cannot be initialized. A similar problem happens if an initWithArray: initializer is passed an NSDictionary object instead of an NSArray object. When an init... method cannot initialize an object, it should: ● Release the newly allocated object (in memory-managed code) ● Return nil Returning nil from an initializer indicates that the requested object cannot be created. When you create an object, you should generally check whether the returned value is nil before proceeding: Object Initialization Issues with Initializers 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 36id anObject = [[MyClass alloc] init]; if (anObject) { [anObject doSomething]; // more messages... } else { // handle error } Because an init... method might return nil or an object other than the one explicitly allocated, it is dangerous to use the instance returned by alloc or allocWithZone: instead of the one returned by the initializer. Consider the following code: id myObject = [MyClass alloc]; [myObject init]; [myObject doSomething]; The init method in this example could have returned nil or could have substituted a different object. Because you can send a message to nil without raising an exception, nothing would happen in the former case except (perhaps) a debugging headache. But you should always rely on the initialized instance instead of the “raw” just-allocated one. Therefore, you should nest the allocation message inside the initialization message and test the object returned from the initializer before proceeding. id myObject = [[MyClass alloc] init]; if ( myObject ) { [myObject doSomething]; } else { // error recovery... } Once an object is initialized, you should not initialize it again. If you attempt a reinitialization, the framework class of the instantiated object often raises an exception. For example, the second initialization in this example would result in NSInvalidArgumentException being raised. NSString *aStr = [[NSString alloc] initWithString:@"Foo"]; aStr = [aStr initWithString:@"Bar"]; Object Initialization Issues with Initializers 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 37Implementing an Initializer There are several critical rules to follow when implementing an init... method that serves as a class’s sole initializer or, if there are multiple initializers, its designated initializer (described in “Multiple Initializers and the Designated Initializer” (page 40)): ● Always invoke the superclass (super) initializer first. ● Check the object returned by the superclass. If it is nil, then initialization cannot proceed; return nil to the receiver. ● When initializing instance variables that are references to objects, retain or copy the object as necessary (in memory-managed code). ● After setting instance variables to valid initial values, return self unless: ● It was necessary to return a substituted object, in which case release the freshly allocated object first (in memory-managed code). ● A problem prevented initialization from succeeding, in which case return nil. - (id)initWithAccountID:(NSString *)identifier { if ( self = [super init] ) { Account *ac = [accountDictionary objectForKey:identifier]; if (ac) { // object with that ID already exists [self release]; return [ac retain]; } if (identifier) { accountID = [identifier copy]; // accountID is instance variable [accountDictionary setObject:self forKey:identifier]; return self; } else { [self release]; return nil; } } else return nil; } Object Initialization Implementing an Initializer 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 38Note: Although, for the sake of simplicity, this example returns nil if the parameter is nil, the better Cocoa practice is to raise an exception. It isn’t necessary to initialize all instance variables of an object explicitly, just those that are necessary to make the object functional. The default set-to-zero initialization performed on an instance variable during allocation is often sufficient. Make sure that you retain or copy instance variables, as required for memory management. The requirement to invoke the superclass’s initializer as the first action is important. Recall that an object encapsulates not only the instance variables defined by its class but the instance variables defined by all of its ancestor classes. By invoking the initializer of super first, you help to ensure that the instance variables defined by classes up the inheritance chain are initialized first. The immediate superclass, in its initializer, invokes the initializer of its superclass, which invokes the main init... method of its superclass, and so on (see Figure 6-1). The proper order of initialization is critical because the later initializations of subclasses may depend on superclass-defined instance variables being initialized to reasonable values. Figure 6-1 Initialization up the inheritance chain super super Class A Class B Class C inherits from inherits from self - (id)initWithName:birthday: - (id)initWithName: Instance variables: NSString *name: Instance variables: NSString *name: NSDate *dob: - (id)initWithName:birthday:ssn: Instance variables: NSString *name: NSDate *dob: NSNumber *ssn: sets sets sets Object Initialization Implementing an Initializer 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 39Inherited initializers are a concern when you create a subclass. Sometimes a superclass init... method sufficiently initializes instances of your class. But because it is more likely it won’t, you should override the superclass’s initializer. If you don’t, the superclass’s implementation is invoked, and because the superclass knows nothing about your class, your instances may not be correctly initialized. Multiple Initializers and the Designated Initializer A class can define more than one initializer. Sometimes multiple initializers let clients of the class provide the input for the same initialization in different forms. The NSSet class, for example, offers clientsseveral initializers that accept the same data in different forms; one takes an NSArray object, another a counted list of elements, and another a nil-terminated list of elements: - (id)initWithArray:(NSArray *)array; - (id)initWithObjects:(id *)objects count:(unsigned)count; - (id)initWithObjects:(id)firstObj, ...; Some subclasses provide convenience initializers that supply default values to an initializer that takes the full complement of initialization parameters. Thisinitializer is usually the designated initializer, the most important initializer of a class. For example, assume there is a Task class and it declares a designated initializer with this signature: - (id)initWithTitle:(NSString *)aTitle date:(NSDate *)aDate; The Task class might include secondary, or convenience, initializersthatsimply invoke the designated initializer, passing it default values for those parameters the secondary initializer doesn’t explicitly request. This example shows a designated initializer and a secondary initializer. - (id)initWithTitle:(NSString *)aTitle { return [self initWithTitle:aTitle date:[NSDate date]]; } - (id)init { return [self initWithTitle:@"Task"]; } Object Initialization Multiple Initializers and the Designated Initializer 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 40The designated initializer plays an important role for a class. It ensures that inherited instance variables are initialized by invoking the designated initializer of the superclass. It is typically the init... method that has the most parameters and that does most of the initialization work, and it is the initializer that secondary initializers of the class invoke with messages to self. When you define a subclass, you must be able to identify the designated initializer of the superclass and invoke it in your subclass’s designated initializer through a message to super. You must also make sure that inherited initializers are covered in some way. And you may provide as many convenience initializers as you deem necessary. When designing the initializers of your class, keep in mind that designated initializers are chained to each other through messages to super; whereas other initializers are chained to the designated initializer of their class through messages to self. An example will make this clearer. Let’s say there are three classes, A, B, and C; class B inherits from class A, and class C inherits from class B. Each subclass adds an attribute as an instance variable and implements an init... method—the designated initializer—to initialize this instance variable. They also define secondary initializers and ensure that inherited initializers are overridden, if necessary. Figure 6-2 illustrates the initializers of all three classes and their relationships. Figure 6-2 Interactions of secondary and designated initializers - (id)init super super Class A Class B Class C inherits from inherits from self - (id)init - (id)initWithTitle: self - (id)initWithTitle: - (id)initWithTitle:date: Object Initialization Multiple Initializers and the Designated Initializer 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 41The designated initializer for each class is the initializer with the most coverage; it is the method that initializes the attribute added by the subclass. The designated initializer is also the init... method that invokes the designated initializer of the superclass in a message to super. In this example, the designated initializer of class C, initWithTitle:date:, invokesthe designated initializer of itssuperclass, initWithTitle:, which in turn invokes the init method of class A. When creating a subclass, it’s always important to know the designated initializer of the superclass. Although designated initializers are thus connected up the inheritance chain through messages to super, secondary initializers are connected to their class’s designated initializer through messagesto self. Secondary initializers (as in this example) are frequently overridden versions of inherited initializers. Class C overrides initWithTitle: to invoke its designated initializer, passing it a default date. This designated initializer, in turn, invokes the designated initializer of class B, which is the overridden method, initWithTitle:. If you sent an initWithTitle: message to objects of class B and class C, you’d be invoking different method implementations. On the other hand, if class C did not override initWithTitle: and you sent the message to an instance of class C, the class B implementation would be invoked. Consequently, the C instance would be incompletely initialized (since it would lack a date). When creating a subclass, it’s important to make sure that all inherited initializers are adequately covered. Sometimes the designated initializer of a superclass may be sufficient for the subclass, and so there is no need for the subclass to implement its own designated initializer. Other times, a class’s designated initializer may be an overridden version of its superclass's designated initializer. This is frequently the case when the subclass needs to supplement the work performed by the superclass’s designated initializer, even though the subclass does not add any instance variables of its own (or the instance variables it does add don’t require explicit initialization). Object Initialization Multiple Initializers and the Designated Initializer 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 42The Model-View-Controller design pattern (MVC) is quite old. Variations of it have been around at least since the early days of Smalltalk. It is a high-level pattern in that it concerns itself with the global architecture of an application and classifies objects according to the general rolesthey play in an application. It is also a compound pattern in that it comprises several, more elemental patterns. Object-oriented programs benefit in several ways by adapting the MVC design pattern for their designs. Many objectsin these programstend to be more reusable and their interfacestend to be better defined. The programs overall are more adaptable to changing requirements—in other words, they are more easily extensible than programs that are not based on MVC. Moreover, many technologies and architectures in Cocoa—such as bindings, the document architecture, and scriptability—are based on MVC and require that your custom objects play one of the roles defined by MVC. Roles and Relationships of MVC Objects The MVC design pattern considersthere to be three types of objects: model objects, view objects, and controller objects. The MVC pattern defines the roles that these types of objects play in the application and their lines of communication. When designing an application, a major step is choosing—or creating custom classes for—objects that fall into one of these three groups. Each of the three types of objects is separated from the others by abstract boundaries and communicates with objects of the other types across those boundaries. Model Objects Encapsulate Data and Basic Behaviors Model objects represent special knowledge and expertise. They hold an application’s data and define the logic that manipulates that data. A well-designed MVC application has all its important data encapsulated in model objects. Any data that is part of the persistent state of the application (whether that persistent state is stored in files or databases) should reside in the model objects once the data is loaded into the application. Because they represent knowledge and expertise related to a specific problem domain, they tend to be reusable. Ideally, a model object has no explicit connection to the user interface used to present and edit it. For example, if you have a model object that represents a person (say you are writing an address book), you might want to store a birthdate. That’s a good thing to store in your Person model object. However, storing a date format string or other information on how that date is to be presented is probably better off somewhere else. 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 43 Model-View-ControllerIn practice, thisseparation is not alwaysthe best thing, and there issome room for flexibility here, but in general a model object should not be concerned with interface and presentation issues. One example where a bit of an exception isreasonable is a drawing application that has model objectsthat represent the graphics displayed. It makes sense for the graphic objects to know how to draw themselves because the main reason for their existence is to define a visual thing. But even in this case, the graphic objects should not rely on living in a particular view or any view at all, and they should not be in charge of knowing when to draw themselves. They should be asked to draw themselves by the view object that wants to present them. View Objects Present Information to the User A view object knows how to display, and might allow users to edit, the data from the application’s model. The view should not be responsible forstoring the data it is displaying. (This does not mean the view never actually stores data it’s displaying, of course. A view can cache data or do similar tricks for performance reasons). A view object can be in charge of displaying just one part of a model object, or a whole model object, or even many different model objects. Views come in many different varieties. View objects tend to be reusable and configurable, and they provide consistency between applications. In Cocoa, the AppKit framework defines a large number of view objects and provides many of them in the Interface Builder library. By reusing the AppKit’s view objects, such as NSButton objects, you guarantee that buttons in your application behave just like buttonsin any other Cocoa application, assuring a high level of consistency in appearance and behavior across applications. A view should ensure it is displaying the model correctly. Consequently, it usually needsto know about changes to the model. Because model objects should not be tied to specific view objects, they need a generic way of indicating that they have changed. Controller Objects Tie the Model to the View A controller object acts as the intermediary between the application's view objects and its model objects. Controllers are often in charge of making sure the views have access to the model objects they need to display and act as the conduit through which views learn about changes to the model. Controller objects can also perform set-up and coordinating tasks for an application and manage the life cycles of other objects. In a typical Cocoa MVC design, when users enter a value or indicate a choice through a view object, that value or choice is communicated to a controller object. The controller object might interpret the user input in some application-specific way and then either may tell a model object what to do with thisinput—for example, "add a new value" or "delete the current record"—or it may have the model object reflect a changed value in one of its properties. Based on this same user input, some controller objects might also tell a view object to change an aspect of its appearance or behavior, such as telling a button to disable itself. Conversely, when a model object changes—say, a new data source is accessed—the model object usually communicates that change to a controller object, which then requests one or more view objects to update themselves accordingly. Model-View-Controller Roles and Relationships of MVC Objects 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 44Controller objects can be either reusable or nonreusable, depending on their general type. “Types of Cocoa Controller Objects” (page 45) describes the different types of controller objects in Cocoa. Combining Roles One can merge the MVC roles played by an object, making an object, for example, fulfill both the controller and view roles—in which case, it would be called a view controller. In the same way, you can also have model-controller objects. For some applications, combining roles like this is an acceptable design. A model controller is a controller that concerns itself mostly with the model layer. It “owns” the model; its primary responsibilities are to manage the model and communicate with view objects. Action methods that apply to the model as a whole are typically implemented in a model controller. The document architecture provides a number of these methods for you; for example, an NSDocument object (which is a central part of the document architecture) automatically handles action methods related to saving files. A view controller is a controller that concerns itself mostly with the view layer. It “owns” the interface (the views); its primary responsibilities are to manage the interface and communicate with the model. Action methods concerned with data displayed in a view are typically implemented in a view controller. An NSWindowController object (also part of the document architecture) is an example of a view controller. “Design Guidelinesfor MVC Applications” (page 50) offerssome design advice concerning objects with merged MVC roles. FurtherReading: Document-BasedApplicationsOverview discussesthedistinctionbetweenamodel controller and a view controller from another perspective. Types of Cocoa Controller Objects “Controller Objects Tie the Model to the View” (page 44) sketches the abstract outline of a controller object, but in practice the picture is far more complex. In Cocoa there are two general kinds of controller objects: mediating controllers and coordinating controllers. Each kind of controller object is associated with a different set of classes and each provides a different range of behaviors. A mediating controller is typically an object that inherits from the NSControllerclass. Mediating controller objects are used in the Cocoa bindings technology. They facilitate—or mediate—the flow of data between view objects and model objects. Model-View-Controller Types of Cocoa Controller Objects 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 45iOS Note: AppKit implements the NSController class and its subclasses. These classes and the bindings technology are not available in iOS. Mediating controllers are typically ready-made objects that you drag from the Interface Builder library. You can configure these objects to establish the bindings between properties of view objects and properties of the controller object, and then between those controller properties and specific properties of a model object. As a result, when users change a value displayed in a view object, the new value is automatically communicated to a model object forstorage—via the mediating controller; and when a property of a model changesits value, that change is communicated to a view for display. The abstract NSController class and its concrete subclasses—NSObjectController, NSArrayController, NSUserDefaultsController, and NSTreeController—provide supporting features such as the ability to commit and discard changes and the management of selections and placeholder values. A coordinating controller istypically an NSWindowController or NSDocumentControllerobject (available only in AppKit), or an instance of a custom subclass of NSObject. Its role in an application is to oversee—or coordinate—the functioning of the entire application or of part of the application,such asthe objects unarchived from a nib file. A coordinating controller provides services such as: ● Responding to delegation messages and observing notifications ● Responding to action messages ● Managing the life cycle of owned objects (for example, releasing them at the proper time) ● Establishing connections between objects and performing other set-up tasks NSWindowController and NSDocumentController are classes that are part of the Cocoa architecture for document-based applications. Instances of these classes provide default implementations for several of the services listed above, and you can create subclasses of them to implement more application-specific behavior. You can even use NSWindowController objects to manage windows in an application that is not based on the document architecture. A coordinating controller frequently owns the objects archived in a nib file. As File’s Owner, the coordinating controller is external to the objects in the nib file and manages those objects. These owned objects include mediating controllers as well as window objects and view objects. See “MVC as a Compound Design Pattern” (page 47) for more on coordinating controllers as File's Owner. Instances of custom NSObject subclasses can be entirely suitable as coordinating controllers. These kinds of controller objects combine both mediating and coordinating functions. For their mediating behavior, they make use of mechanismssuch astarget-action, outlets, delegation, and notificationsto facilitate the movement of data between view objects and model objects. They tend to contain a lot of glue code and, because that code is exclusively application-specific, they are the least reusable kind of object in an application. Model-View-Controller Types of Cocoa Controller Objects 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 46Further Reading: For more on the Cocoa bindings technology, see Cocoa Bindings Programming Topics. MVC as a Compound Design Pattern Model-View-Controller is a design pattern that is composed of several more basic design patterns. These basic patterns work together to define the functional separation and paths of communication that are characteristic of an MVC application. However, the traditional notion of MVC assigns a set of basic patterns different from those that Cocoa assigns. The difference primarily lies in the roles given to the controller and view objects of an application. In the original (Smalltalk) conception, MVC is made up of the Composite, Strategy, and Observer patterns. ● Composite—The view objectsin an application are actually a composite of nested viewsthat work together in a coordinated fashion (that is, the view hierarchy). These display components range from a window to compound views, such as a table view, to individual views, such as buttons. User input and display can take place at any level of the composite structure. ● Strategy—A controller object implements the strategy for one or more view objects. The view object confines itself to maintaining its visual aspects, and it delegates to the controller all decisions about the application-specific meaning of the interface behavior. ● Observer—A model object keeps interested objects in an application—usually view objects—advised of changes in its state. The traditional way the Composite, Strategy, and Observer patterns work together is depicted by Figure 7-1: The user manipulates a view at some level of the composite structure and, as a result, an event is generated. A controller object receives the event and interprets it in an application-specific way—that is, it applies a strategy. This strategy can be to request (via message) a model object to change its state or to request a view Model-View-Controller MVC as a Compound Design Pattern 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 47object (at some level of the composite structure) to change its behavior or appearance. The model object, in turn, notifies all objects who have registered as observers when its state changes; if the observer is a view object, it may update its appearance accordingly. Figure 7-1 Traditional version of MVC as a compound pattern User action Update Get changed state Update Strategy Controller Composite View Notify Observer Model The Cocoa version of MVC as a compound pattern has some similarities to the traditional version, and in fact it is quite possible to construct a working application based on the diagram in Figure 7-1. By using the bindings technology, you can easily create a Cocoa MVC application whose views directly observe model objects to receive notifications of state changes. However, there is a theoretical problem with this design. View objects and model objects should be the most reusable objects in an application. View objects represent the "look and feel" of an operating system and the applications that system supports; consistency in appearance and behavior is essential, and that requires highly reusable objects. Model objects by definition encapsulate the data associated with a problem domain and perform operations on that data. Design-wise, it's best to keep model and view objects separate from each other, because that enhances their reusability. In most Cocoa applications, notifications of state changes in model objects are communicated to view objects through controller objects. Figure 7-2 shows this different configuration, which appears much cleaner despite the involvement of two more basic design patterns. Figure 7-2 Cocoa version of MVC as a compound design pattern User action Update Update Notify Mediator Strategy Controller View Model Command Composite Observer Model-View-Controller MVC as a Compound Design Pattern 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 48The controller object in this compound design pattern incorporatesthe Mediator pattern as well asthe Strategy pattern; it mediates the flow of data between model and view objects in both directions. Changes in model state are communicated to view objects through the controller objects of an application. In addition, view objects incorporate the Command pattern through their implementation of the target-action mechanism. Note: The target-action mechanism, which enables view objects to communicate user input and choices, can be implemented in both coordinating and mediating controller objects. However, the design of the mechanism differs in each controller type. For coordinating controllers, you connect the view object to its target (the controller object) in Interface Builder and specify an action selector that must conform to a certain signature. Coordinating controllers, by virtue of being delegates of windows and the global application object, can also be in the responder chain. The bindings mechanism used by mediating controllers also connects view objects to targets and allows action signatures with a variable number of parameters of arbitrary types. Mediating controllers, however, aren’t in the responder chain. There are practical reasons as well as theoretical ones for the revised compound design pattern depicted in Figure 7-2, especially when it comesto the Mediator design pattern. Mediating controllers derive from concrete subclasses of NSController, and these classes, besides implementing the Mediator pattern, offer many features that applications should take advantage of, such as the management of selections and placeholder values. And if you opt not to use the bindings technology, your view object could use a mechanism such as the Cocoa notification center to receive notifications from a model object. But this would require you to create a custom view subclass to add the knowledge of the notifications posted by the model object. Model-View-Controller MVC as a Compound Design Pattern 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 49In a well-designed Cocoa MVC application, coordinating controller objects often own mediating controllers, which are archived in nib files. Figure 7-3 shows the relationships between the two types of controller objects. Figure 7-3 Coordinating controller as the owner of a nib file Owns Coordinating Controller Nib file Data flow Data flow View Mediating Controller Model Design Guidelines for MVC Applications The following guidelines apply to Model-View-Controller considerations in the design of applications: ● Although you can use an instance of a custom subclass of NSObject as a mediating controller, there's no reason to go through all the work required to make it one. Use instead one of the ready-made NSController objects designed for the Cocoa bindings technology; that is, use an instance of NSObjectController, NSArrayController, NSUserDefaultsController, or NSTreeController—or a custom subclass of one of these concrete NSController subclasses. However, if the application is very simple and you feel more comfortable writing the glue code needed to implement mediating behavior using outlets and target-action, feel free to use an instance of a custom NSObject subclass as a mediating controller. In a custom NSObject subclass, you can also implement a mediating controller in the NSController sense, using key-value coding, key-value observing, and the editor protocols. Model-View-Controller Design Guidelines for MVC Applications 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 50● Although you can combine MVC roles in an object, the best overall strategy is to keep the separation between roles. This separation enhances the reusability of objects and the extensibility of the program they're used in. If you are going to merge MVC roles in a class, pick a predominant role for that class and then (for maintenance purposes) use categories in the same implementation file to extend the class to play other roles. ● A goal of a well-designed MVC application should be to use as many objects as possible that are (theoretically, at least) reusable. In particular, view objects and model objects should be highly reusable. (The ready-made mediating controller objects, of course, are reusable.) Application-specific behavior is frequently concentrated as much as possible in controller objects. ● Although it is possible to have views directly observe models to detect changes in state, it is best not to do so. A view object should always go through a mediating controller object to learn about changes in an model object. The reason is two-fold: ● If you use the bindings mechanism to have view objects directly observe the properties of model objects, you bypass all the advantages that NSController and its subclasses give your application: selection and placeholder management as well as the ability to commit and discard changes. ● If you don't use the bindings mechanism, you have to subclass an existing view classto add the ability to observe change notifications posted by a model object. ● Strive to limit code dependency in the classes of your application. The greater the dependency a class has on another class, the less reusable it is. Specific recommendations vary by the MVC roles of the two classes involved: ● A view classshouldn't depend on a model class(although this may be unavoidable with some custom views). ● A view class shouldn't have to depend on a mediating controller class. ● A model class shouldn't depend on anything other than other model classes. ● A mediating controller class shouldn’t depend on a model class (although, like views, this may be necessary if it's a custom controller class). ● A mediating controller class shouldn't depend on view classes or on coordinating controller classes. ● A coordinating controller class depends on classes of all MVC role types. ● If Cocoa offers an architecture that solves a programming problem, and this architecture assigns MVC roles to objects of specific types, use that architecture. It will be much easier to put your project together if you do. The document architecture, for example, includes an Xcode project template that configures an NSDocument object (per-nib model controller) as File's Owner. Model-View-Controller Design Guidelines for MVC Applications 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 51Model-View-Controller in Cocoa (OS X) The Model-View-Controller design pattern is fundamental to many Cocoa mechanisms and technologies. As a consequence, the importance of using MVC in object-oriented design goes beyond attaining greater reusability and extensibility for your own applications. If your application is to incorporate a Cocoa technology that is MVC-based, your application will work best if its design also follows the MVC pattern. It should be relatively painless to use these technologies if your application has a good MVC separation, but it will take more effort to use such a technology if you don’t have a good separation. Cocoa in OS X includes the following architectures, mechanisms, and technologies that are based on Model-View-Controller: ● Document architecture. In this architecture, a document-based application consists of a controller object for the entire application (NSDocumentController), a controller object for each document window (NSWindowController), and an object that combines controller and model roles for each document (NSDocument). ● Bindings. MVC is central to the bindings technology of Cocoa. The concrete subclasses of the abstract NSController provide ready-made controller objects that you can configure to establish bindings between view objects and properly designed model objects. ● Application scriptability. When designing an application to make it scriptable, it is essential not only that it follow the MVC design pattern but that your application’s model objects are properly designed. Scripting commandsthat access application state and request application behaviorshould usually be sent to model objects or controller objects. ● Core Data. The Core Data framework manages graphs of model objects and ensures the persistence of those objects by saving them to (and retrieving them from) a persistentstore. Core Data istightly integrated with the Cocoa bindings technology. The MVC and object modeling design patterns are essential determinants of the Core Data architecture. ● Undo. In the undo architecture, model objects once again play a central role. The primitive methods of model objects (which are usually its accessor methods) are often where you implement undo and redo operations. The view and controller objects of an action may also be involved in these operations; for example, you might have such objects give specific titles to the undo and redo menu items, or you might have them undo selections in a text view. Model-View-Controller Model-View-Controller in Cocoa (OS X) 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 52This section defines terms and presents examples of object modeling and key-value coding that are specific to Cocoa bindings and the Core Data framework. Understanding terms such as key paths is fundamental to using these technologies effectively. This section is recommended reading if you are new to object-oriented design or key-value coding. When using the Core Data framework, you need a way to describe your model objects that does not depend on views and controllers. In a good reusable design, views and controllers need a way to access model properties without imposing dependencies between them. The Core Data framework solves this problem by borrowing concepts and terms from database technology—specifically, the entity-relationship model. Entity-relationship modeling is a way of representing objects typically used to describe a data source’s data structures in a way that allows those data structures to be mapped to objects in an object-oriented system. Note that entity-relationship modeling isn’t unique to Cocoa; it’s a popular discipline with a set of rules and terms that are documented in database literature. It is a representation that facilitates storage and retrieval of objects in a data source. A data source can be a database, a file, a web service, or any other persistent store. Because it is not dependent on any type of data source it can also be used to represent any kind of object and its relationship to other objects. In the entity-relationship model, the objects that hold data are called entities, the components of an entity are called attributes, and the referencesto other data-bearing objects are called relationships. Together, attributes and relationships are known as properties. With these three simple components (entities, attributes, and relationships), you can model systems of any complexity. Cocoa uses a modified version of the traditional rules of entity-relationship modeling referred to in this document as object modeling . Object modeling is particularly useful in representing model objects in the Model-View-Controller (MVC) design pattern. Thisis notsurprising because even in a simple Cocoa application, models are typically persistent—that is, they are stored in a data container such as a file. Entities Entities are model objects. In the MVC design pattern, model objects are the objects in your application that encapsulate specified data and provide methods that operate on that data. They are usually persistent but more importantly, model objects are not dependent on how the data is displayed to the user. 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 53 Object ModelingFor example, a structured collection of model objects (an object model) can be used to represent a company’s customer base, a library of books, or a network of computers. A library book has attributes—such as the book title, ISBN number, and copyright date—and relationships to other objects—such as the author and library member. In theory, if the parts of a system can be identified, the system can be expressed as an object model. Figure 8-1 shows an example object model used in an employee management application. In this model, Department models a department and Employee models an employee. Figure 8-1 Employee management application object diagram Department name budget Employee firstName lastName salary Attributes Attributes represent structures that contain data. An attribute of an object may be a simple value, such as a scalar (for example, an integer, float, or double value), but can also be a C structure (for example an array of char values or an NSPoint structure) or an instance of a primitive class (such as, NSNumber, NSData, or NSColor in Cocoa). Immutable objects such as NSColor are usually considered attributes too. (Note that Core Data natively supports only a specific set of attribute types, as described in NSAttributeDescription Class Reference . You can, however, use additional attribute types, as described in “Non-Standard Persistent Attributes” in Core Data Programming Guide .) Object Modeling Attributes 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 54In Cocoa, an attribute typically corresponds to a model’s instance variable or accessor method. For example, Employee has firstName, lastName, and salary instance variables. In an employee management application, you might implement a table view to display a collection of Employee objects and some of their attributes, as shown in Figure 8-2. Each row in the table correspondsto an instance of Employee, and each column corresponds to an attribute of Employee. Figure 8-2 Employees table view Relationships Not all properties of a model are attributes—some properties are relationshipsto other objects. Your application is typically modeled by multiple classes. At runtime, your object model is a collection of related objects that make up an object graph. These are typically the persistent objects that your users create and save to some data container or file before terminating the application (asin a document-based application). The relationships between these model objects can be traversed at runtime to access the properties of the related objects. For example, in the employee management application, there are relationships between an employee and the department in which the employee works, and between an employee and the employee’s manager. Because a manager is also an employee, the employee–manager relationship is an example of a reflexive relationship—a relationship from an entity to itself. Relationships are inherently bidirectional, so conceptually at least there are also relationships between a department and the employees that work in the department, and an employee and the employee’s direct reports. Figure 8-3 (page 56) illustrates the relationships between a Department and an Employee entity, and the Employee reflexive relationship. In this example, the Department entity’s “employees” relationship is the inverse of the Employee entity’s “department” relationship. It is possible, however, for relationships to be navigable in only one direction—for there to be no inverse relationship. If, for example, you are never interested in finding out from a department object what employees are associated with it, then you do not have to model Object Modeling Relationships 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 55that relationship. (Note that although thisistrue in the general case, Core Data may impose additional constraints over general Cocoa object modeling—not modeling the inverse should be considered an extremely advanced option.) Figure 8-3 Relationships in the employee management application Department name budget Employee firstName lastName salary department employees manager directReports Relationship Cardinality and Ownership Every relationship has a cardinality ; the cardinality tells you how many destination objects can (potentially) resolve the relationship. If the destination object is a single object, then the relationship is called a to-one relationship . If there may be more than one object in the destination, then the relationship is called a to-many relationship . Relationships can be mandatory or optional. A mandatory relationship is one where the destination is required—for example, every employee must be associated with a department. An optional relationship is, as the name suggests, optional—for example, not every employee has direct reports. So the directReports relationship depicted in Figure 8-4 (page 56) is optional. It is also possible to specify a range for the cardinality. An optional to-one relationship has a range 0-1. An employee may have any number of direct reports, or a range that specifies a minimum and a maximum, for example, 0-15, which also illustrates an optional to-many relationship. Figure 8-4 illustrates the cardinalities in the employee management application. The relationship between an Employee object and a Department object is a mandatory to-one relationship—an employee must belong to one, and only one, department. The relationship between a Department and its Employee objectsis an optional to-many relationship (represented by a “*”). The relationship between an employee and a manager is an optional to-one relationship (denoted by the range 0-1)—top-ranking employees do not have managers. Figure 8-4 Relationship cardinality 1 department employees * 0..1 manager * directReports Department name budget Employee firstName lastName salary Note also that destination objects of relationships are sometimes owned and sometimes shared. Object Modeling Relationships 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 56Accessing Properties In order for models, views, and controllers to be independent of each other, you need to be able to access properties in a way that is independent of a model’s implementation. This is accomplished by using key-value pairs. Keys You specify properties of a model using a simple key, often a string. The corresponding view or controller uses the key to look up the corresponding attribute value. This design enforces the notion that the attribute itself doesn’t necessarily contain the data—the value can be indirectly obtained or derived. Key-value coding is used to perform thislookup; it is a mechanism for accessing an object’s propertiesindirectly and, in certain contexts, automatically. Key-value coding works by using the names of the object’s properties—typically itsinstance variables or accessor methods—as keysto accessthe values of those properties. For example, you might obtain the name of a Department object using a name key. If the Department object either has an instance variable or a method called name then a value for the key can be returned (if it doesn’t have either, an error is returned). Similarly, you might obtain Employee attributes using the firstName, lastName, and salary keys. Values All values for a particular attribute of a given entity are of the same data type. The data type of an attribute is specified in the declaration of its corresponding instance variable or in the return value of its accessor method. For example, the data type of the Department object name attribute may be an NSString object in Objective-C. Note that key-value coding returns only object values. If the return type or the data type for the specific accessor method or instance variable used to supply the value for a specified key is not an object, then an NSNumber or NSValue object is created for that value and returned in its place. If the name attribute of Department is of type NSString, then, using key-value coding, the value returned for the name key of a Department object is an NSString object. If the budget attribute of Department is of type float, then, using key-value coding, the value returned for the budget key of a Department object is an NSNumber object. Similarly, when you set a value using key-value coding, if the data type required by the appropriate accessor or instance variable for the specified key is not an object, then the value is extracted from the passed object using the appropriate -typeValue method. The value of a to-one relationship is simply the destination object of that relationship. For example, the value of the department property of an Employee object is a Department object. The value of a to-many relationship is the collection object. The collection can be a set or an array. If you use Core Data it is a set; otherwise, it is Object Modeling Accessing Properties 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 57typically an array) that contains the destination objects of that relationship. For example, the value of the employees property of an Department object is a collection containing Employee objects. Figure 8-5 shows an example object graph for the employee management application. Figure 8-5 Object graph for the employee management application Department name: "Marketing" budget: 2000000 employees Collection Collection Employee firstName: "Toni" lastName: "Lau" salary: 7000 manager department directReports Employee firstName: "Joe" lastName: "Jackson" salary: 5000 manager department directReports Key Paths A key path is a string of dot-separated keysthatspecify a sequence of object propertiesto traverse. The property of the first key is determined by, and each subsequent key is evaluated relative to, the previous property. Key paths allow you to specify the properties of related objects in a way that is independent of the model implementation. Using key paths you can specify the path through an object graph, of whatever depth, to a specific attribute of a related object. The key-value coding mechanism implements the lookup of a value given a key path similar to key-value pairs. For example, in the employee-management application you might access the name of a Department via an Employee object using the department.name key path where department is a relationship of Employee and name is an attribute of Department. Key paths are useful if you want to display an attribute of a destination Object Modeling Accessing Properties 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 58entity. For example, the employee table view in Figure 8-6 is configured to display the name of the employee’s department object, not the department object itself. Using Cocoa bindings, the value of the Department column is bound to department.name of the Employee objects in the displayed array. Figure 8-6 Employees table view showing department name Not every relationship in a key path necessarily has a value. For example, the manager relationship can be nil if the employee is the CEO. In this case, the key-value coding mechanism does not break—it simply stops traversing the path and returns an appropriate value, such as nil. Object Modeling Accessing Properties 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 59Cocoa objects are either mutable or immutable. You cannot change the encapsulated values of immutable objects; once such an object is created, the value it represents remains the same throughout the object’s life. But you can change the encapsulated value of a mutable object at any time. The following sections explain the reasons for having mutable and immutable variants of an object type, describe the characteristics and side-effects of object mutability, and recommend how best to handle objects when their mutability is an issue. Why Mutable and Immutable Object Variants? Objects by default are mutable. Most objects allow you to change their encapsulated data through setter accessor methods. For example, you can change the size, positioning, title, buffering behavior, and other characteristics of an NSWindow object. A well-designed model object—say, an object representing a customer record—requires setter methods to change its instance data. The Foundation framework adds some nuance to this picture by introducing classes that have mutable and immutable variants. The mutable subclasses are typically subclasses of their immutable superclass and have “Mutable” embedded in the class name. These classes include the following: NSMutableArray NSMutableDictionary NSMutableSet NSMutableIndexSet NSMutableCharacterSet NSMutableData NSMutableString NSMutableAttributedString NSMutableURLRequest 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 60 Object MutabilityNote: Except for NSMutableParagraphStyle in the AppKit framework, the Foundation framework currently defines all explicitly named mutable classes. However, any Cocoa framework can potentially have its own mutable and immutable class variants. Although these classes have atypical names, they are closer to the mutable norm than their immutable counterparts. Why this complexity? What purpose does having an immutable variant of a mutable objectserve? Consider a scenario where all objects are capable of being mutated. In your application you invoke a method and are handed back a reference to an object representing a string. You use this string in your user interface to identify a particular piece of data. Now another subsystem in your application gets its own reference to that same string and decidesto mutate it. Suddenly your label has changed out from under you. Things can become even more dire if, for instance, you get a reference to an array that you use to populate a table view. The user selects a row corresponding to an object in the array that has been removed by some code elsewhere in the program, and problems ensue. Immutability is a guarantee that an object won’t unexpectedly change in value while you’re using it. Objects that are good candidates for immutability are ones that encapsulate collections of discrete values or contain values that are stored in buffers (which are themselves kinds of collections, either of characters or bytes). But not all such value objects necessarily benefit from having mutable versions. Objects that contain a single simple value, such as instances of NSNumber or NSDate, are not good candidates for mutability. When the represented value changes in these cases, it makes more sense to replace the old instance with a new instance. Performance is also a reason for immutable versions of objects representing things such as strings and dictionaries. Mutable objectsfor basic entitiessuch asstrings and dictionaries bring some overhead with them. Because they must dynamically manage a changeable backing store—allocating and deallocating chunks of memory as needed—mutable objects can be less efficient than their immutable counterparts. Although in theory immutability guarantees that an object’s value is stable, in practice this guarantee isn’t always assured. A method may choose to hand out a mutable object under the return type of its immutable variant; later, it may decide to mutate the object, possibly violating assumptions and choices the recipient has made based on the earlier value. The mutability of an object itself may change as it undergoes various transformations. For example, serializing a property list (using the NSPropertyListSerialization class) does not preserve the mutability aspect of objects, only their general kind—a dictionary, an array, and so on. Thus, when you deserialize this property list, the resulting objects might not be of the same class asthe original objects. For instance, what was once an NSMutableDictionary object might now be a NSDictionary object. Object Mutability Why Mutable and Immutable Object Variants? 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 61Programming with Mutable Objects When the mutability of objects is an issue, it’s best to adopt some defensive programming practices. Here are a few general rules or guidelines: ● Use a mutable variant of an object when you need to modify its contents frequently and incrementally after it has been created. ● Sometimes it’s preferable to replace one immutable object with another; for example, most instance variables that hold string values should be assigned immutable NSString objects that are replaced with setter methods. ● Rely on the return type for indications of mutability. ● If you have any doubts about whether an object is, or should be, mutable, go with immutable. This section explores the gray areas in these guidelines, discussing typical choices you have to make when programming with mutable objects. It also gives an overview of methods in the Foundation framework for creating mutable objects and for converting between mutable and immutable object variants. Creating and Converting Mutable Objects You can create a mutable object through the standard nested alloc-init message—for example: NSMutableDictionary *mutDict = [[NSMutableDictionary alloc] init]; However, many mutable classes offer initializers and factory methodsthat let you specify the initial or probable capacity of the object, such as the arrayWithCapacity: class method of NSMutableArray: NSMutableArray *mutArray = [NSMutableArray arrayWithCapacity:[timeZones count]]; The capacity hint enables more efficient storage of the mutable object’s data. (Because the convention for class factory methods is to return autoreleased instances, be sure to retain the object if you wish to keep it viable in your code.) You can also create a mutable object by making a mutable copy of an existing object of that general type. To do so, invoke the mutableCopy method that each immutable super class of a Foundation mutable class implements: NSMutableSet *mutSet = [aSet mutableCopy]; Object Mutability Programming with Mutable Objects 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 62In the other direction, you can send copy to a mutable object to make an immutable copy of the object. Many Foundation classes with immutable and mutable variants include methods for converting between the variants, including: ● typeWithType:—for example, arrayWithArray: ● setType:—for example, setString: (mutable classes only) ● initWithType:copyItems:—for example, initWithDictionary:copyItems: Storing and Returning Mutable Instance Variables In Cocoa development you often have to decide whether to make an instance variable mutable or immutable. For an instance variable whose value can change, such as a dictionary or string, when is it appropriate to make the object mutable? And when is it better to make the object immutable and replace it with another object when its represented value changes? Generally, when you have an object whose contents change wholesale, it’s better to use an immutable object. Strings (NSString) and data objects (NSData) usually fall into this category. If an object is likely to change incrementally, it is a reasonable approach to make it mutable. Collections such as arrays and dictionaries fall into this category. However, the frequency of changes and the size of the collection should be factors in this decision. For example, if you have a small array that seldom changes, it’s better to make it immutable. There are a couple of other considerations when deciding on the mutability of a collection held as an instance variable: ● If you have a mutable collection that is frequently changed and that you frequently hand out to clients (that is, you return it directly in a getter accessor method), you run the risk of mutating something that your clients might have a reference to. If this risk is probable, the instance variable should be immutable. ● If the value of the instance variable frequently changes but you rarely return it to clientsin getter methods, you can make the instance variable mutable but return an immutable copy of it in your accessor method; in memory-managed programs, this object would be autoreleased (Listing 9-1). Listing 9-1 Returning an immutable copy of a mutable instance variable @interface MyClass : NSObject { // ... NSMutableSet *widgets; } // ... @end Object Mutability Programming with Mutable Objects 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 63@implementation MyClass - (NSSet *)widgets { return (NSSet *)[[widgets copy] autorelease]; } One sophisticated approach for handling mutable collections that are returned to clients is to maintain a flag that records whether the object is currently mutable or immutable. If there is a change, make the object mutable and apply the change. When handing out the collection, make the object immutable (if necessary) before returning it. Receiving Mutable Objects The invoker of a method is interested in the mutability of a returned object for two reasons: ● It wants to know if it can change the object’s value. ● It wants to know if the object’s value will change unexpectedly while it has a reference to it. Use Return Type, Not Introspection To determine whether it can change a received object, the receiver of a message must rely on the formal type of the return value. If it receives, for example, an array object typed as immutable, it should not attempt to mutate it. It is not an acceptable programming practice to determine if an object is mutable based on its class membership—for example: if ( [anArray isKindOfClass:[NSMutableArray class]] ) { // add, remove objects from anArray } For reasons related to implementation, what isKindOfClass: returns in this case may not be accurate. But for reasons other than this, you should not make assumptions about whether an object is mutable based on class membership. Your decision should be guided solely by what the signature of the method vending the object says about its mutability. If you are not sure whether an object is mutable or immutable, assume it’s immutable. A couple of examples might help clarify why this guideline is important: Object Mutability Programming with Mutable Objects 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 64● You read a property list from a file. When the Foundation framework processes the list, it notices that various subsets of the property list are identical, so it creates a set of objects that it shares among all those subsets. Afterward you look at the created property list objects and decide to mutate one subset. Suddenly, and without being aware of it, you’ve changed the tree in multiple places. ● You ask NSView for its subviews (with the subviews method) and it returns an object that is declared to be an NSArray but which could be an NSMutableArray internally. Then you pass that array to some other code that, through introspection, determinesit to be mutable and changesit. By changing this array, the code is mutating internal data structures of the NSView class. So don’t make an assumption about object mutability based on what introspection tells you about an object. Treat objects as mutable or not based on what you are handed at the API boundaries (that is, based on the return type). If you need to unambiguously mark an object as mutable or immutable when you passit to clients, pass that information as a flag along with the object. Make Snapshots of Received Objects If you want to ensure that a supposedly immutable object received from a method does not mutate without your knowing about it, you can make snapshots of the object by copying it locally. Then occasionally compare the stored version of the object with the most recent version. If the object has mutated, you can adjust anything in your program that is dependent on the previous version of the object. Listing 9-2 shows a possible implementation of this technique. Listing 9-2 Making a snapshot of a potentially mutable object static NSArray *snapshot = nil; - (void)myFunction { NSArray *thingArray = [otherObj things]; if (snapshot) { if ( ![thingArray isEqualToArray:snapshot] ) { [self updateStateWith:thingArray]; } } snapshot = [thingArray copy]; } A problem with making snapshots of objects for later comparison is that it is expensive. You’re required to make multiple copies of the same object. A more efficient alternative isto use key-value observing. See Key-Value Observing Programming Guide for a description of this protocol. Object Mutability Programming with Mutable Objects 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 65Mutable Objects in Collections Storing mutable objects in collection objects can cause problems. Certain collections can become invalid or even corrupt if objects they contain mutate because, by mutating, these objects can affect the way they are placed in the collection. First, the properties of objects that are keys in hashing collections such as NSDictionary objects or NSSet objects will, if changed, corrupt the collection if the changed properties affect the results of the object’s hash or isEqual: methods. (If the hash method of the objectsin the collection does not depend on their internal state, corruption is less likely.) Second, if an object in an ordered collection such as a sorted array has its properties changed, this might affect how the object compares to other objects in the array, thus rendering the ordering invalid. Object Mutability Programming with Mutable Objects 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 66An outlet is a property of an object that references another object. The reference is archived through Interface Builder. The connections between the containing object and its outlets are reestablished every time the containing object is unarchived from its nib file. The containing object holds an outlet declared as a property with the type qualifier of IBOutlet and a weak option. For example: @interface AppController : NSObject { } @property (weak) IBOutlet NSArray *keywords; Because it is a property, an outlet becomes part of an object’s encapsulated data and is backed by an instance variable. But an outlet is more than a simple property. The connection between an object and its outlets is archived in a nib file; when the nib file is loaded, each connection is unarchived and reestablished, and is thus always available whenever it becomes necessary to send messages to the other object. The type qualifier IBOutlet is a tag applied to an property declaration so that the Interface Builder application can recognize the property as an outlet and synchronize the display and connection of it with Xcode. An outlet is declared as a weak reference (weak) to prevent strong reference cycles. You create and connect an outlet in the Interface Builder feature of Xcode.The property declaration for the outlet must be tagged with the IBOutlet qualifier. An application typically sets outlet connections between its custom controller objects and objects on the user interface, but they can be made between any objects that can be represented as instances in Interface Builder, even between two custom objects. As with any item of object state, you should be able to justify its inclusion in a class; the more outlets an object has, the more memory it takes up. If there are other ways to obtain a reference to an object, such as finding it through its index position in a matrix, or through its inclusion as a function parameter, or through use of a tag (an assigned numeric identifier), you should do that instead. Outlets are a form of object composition, which is a dynamic pattern that requires an object to somehow acquire referencesto its constituent objectsso that it can send messagesto them. It typically holdsthese other objects as properties backed by instance variables. These variables must be initialized with the appropriate references at some point during the execution of the program. 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 67 OutletsThe Receptionist design pattern addresses the general problem of redirecting an event occurring in one execution context of an application to another execution context for handling. It is a hybrid pattern. Although it doesn’t appear in the “Gang of Four” book, it combines elements of the Command, Memo, and Proxy design patterns described in that book. It is also a variant of the Trampoline pattern (which also doesn’t appear in the book); in this pattern, an event initially is received by a trampoline object, so-called because it immediately bounces, or redirects, the event to a target object for handling. The Receptionist Design Pattern in Practice A KVO notification invokes the observeValueForKeyPath:ofObject:change:context: method implemented by an observer. If the change to the property occurs on a secondary thread, the observeValueForKeyPath:ofObject:change:context: code executes on that same thread. There the central object in this pattern, the receptionist, acts as a thread intermediary. As Figure 11-1 illustrates, a receptionist object is assigned as the observer of a model object’s property. The receptionist implements observeValueForKeyPath:ofObject:change:context: to redirect the notification received on a secondary thread to another execution context—the main operation queue, in this case. When the property 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 68 Receptionist Patternchanges, the receptionist receives a KVO notification. The receptionist immediately adds a block operation to the main operation queue; the block contains code—specified by the client—that updates the user interface appropriately. Figure 11-1 Bouncing KVO updates to the main operation queue Main thread self.value = newValue; observeValueForKeyPath: ofObject:change:context: addOperation: modelObject receptionist Secondary Main operation queue thread task You define a receptionist class so that it has the elements it needs to add itself as an observer of a property and then convert a KVO notification into an update task. Thus it must know what object it’s observing, the property of the object that it’s observing, what update task to execute, and what queue to execute it on. Listing 11-1 shows the initial declaration of the RCReceptionist class and its instance variables. Listing 11-1 Declaring the receptionist class @interface RCReceptionist : NSObject { id observedObject; NSString *observedKeyPath; RCTaskBlock task; NSOperationQueue *queue; } Receptionist Pattern The Receptionist Design Pattern in Practice 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 69The RCTaskBlock instance variable is a block object of the following declared type: typedef void (^RCTaskBlock)(NSString *keyPath, id object, NSDictionary *change); These parameters are similar to those of the observeValueForKeyPath:ofObject:change:context: method. Next, the parameter class declares a single class factory method in which an RCTaskBlock object is a parameter: + (id)receptionistForKeyPath:(NSString *)path object:(id)obj queue:(NSOperationQueue *)queue task:(RCTaskBlock)task; It implementsthis method to assign the passed-in value to instance variables of the created receptionist object and to add that object as an observer of the model object’s property, as shown in Listing 11-2. Listing 11-2 The class factory method for creating a receptionist object + (id)receptionistForKeyPath:(NSString *)path object:(id)obj queue:(NSOperationQueue *)queue task:(RCTaskBlock)task { RCReceptionist *receptionist = [RCReceptionist new]; receptionist->task = [task copy]; receptionist->observedKeyPath = [path copy]; receptionist->observedObject = [obj retain]; receptionist->queue = [queue retain]; [obj addObserver:receptionist forKeyPath:path options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:0]; return [receptionist autorelease]; } Note that the code copies the block object instead of retaining it. Because the block was probably created on the stack, it must be copied to the heap so it exists in memory when the KVO notification is delivered. Finally, the parameter class implements the observeValueForKeyPath:ofObject:change:context: method. The implementation (see Listing 11-3) is simple. Receptionist Pattern The Receptionist Design Pattern in Practice 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 70Listing 11-3 Handling the KVO notification - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context { [queue addOperationWithBlock:^{ task(keyPath, object, change); }]; } This code simply enqueues the task onto the given operation queue, passing the task block the observed object, the key path for the changed property, and the dictionary containing the new value. The task is encapsulated in an NSBlockOperation object that executes the task on the queue. The client object supplies the block code that updates the user interface when it creates a receptionist object, as shown in Listing 11-4. Note that when it creates the receptionist object, the client passes in the operation queue on which the block is to be executed, in this case the main operation queue. Listing 11-4 Creating a receptionist object RCReceptionist *receptionist = [RCReceptionist receptionistForKeyPath:@"value" object:model queue:mainQueue task:^(NSString *keyPath, id object, NSDictionary *change) { NSView *viewForModel = [modelToViewMap objectForKey:model]; NSColor *newColor = [change objectForKey:NSKeyValueChangeNewKey]; [[[viewForModel subviews] objectAtIndex:0] setFillColor:newColor]; }]; When to Use the Receptionist Pattern You can adopt the Receptionist design pattern whenever you need to bounce off work to another execution context for handling. When you observe a notification, or implement a block handler, or respond to an action message and you want to ensure that your code executes in the appropriate execution context, you can implement the Receptionist pattern to redirect the work that must be done to that execution context. With the Receptionist pattern, you might even perform some filtering or coalescing of the incoming data before you bounce off a task to processthe data. For example, you could collect data into batches, and then at intervals dispatch those batches elsewhere for processing. Receptionist Pattern When to Use the Receptionist Pattern 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 71One common situation where the Receptionist pattern is useful is key-value observing. In key-value observing, changes to the value of an model object’s property are communicated to observers via KVO notifications. However, changes to a model object can occur on a background thread. This results in a thread mismatch, because changes to a model object’s state typically result in updates to the user interface, and these must occur on the main thread. In this case, you want to redirect the KVO notifications to the main thread. where the updates to an application’s user interface can occur. Receptionist Pattern When to Use the Receptionist Pattern 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 72Although delegation, bindings, and notification are useful for handling certain forms of communication between objects in a program, they are not particularly suitable for the most visible sort of communication. A typical application’s user interface consists of a number of graphical objects, and perhaps the most common of these objects are controls. A control is a graphical analog of a real-world or logical device (button, slider, checkboxes, and so on); as with a real-world control, such as a radio tuner, you use it to convey your intent to some system of which it is a part—that is, an application. The role of a control on a user interface is simple: It interprets the intent of the user and instructs some other object to carry out that request. When a user acts on the control by, say, clicking it or pressing the Return key, the hardware device generates a raw event. The control accepts the event (as appropriately packaged for Cocoa) and translates it into an instruction that is specific to the application. However, events by themselves don't give much information about the user's intent; they merely tell you that the user clicked a mouse button or pressed a key. So some mechanism must be called upon to provide the translation between event and instruction. This mechanism is called target-action . Cocoa uses the target-action mechanism for communication between a control and another object. This mechanism allows the control and, in OS X its cell or cells, to encapsulate the information necessary to send an application-specific instruction to the appropriate object. The receiving object—typically an instance of a custom class—is called the target. The action is the message that the control sends to the target. The object that is interested in the user event—the target—is the one that imparts significance to it, and this significance is usually reflected in the name it gives to the action. The Target A target is a receiver of an action message. A control or, more frequently, its cell holds the target of its action message as an outlet (see “Outlets” (page 67)). The target usually is an instance of one of your custom classes, although it can be any Cocoa object whose class implements the appropriate action method. You can also set a cell’s or control’s target outlet to nil and let the target object be determined at runtime. When the targetis nil,the application object(NSApplication or UIApplication)searchesfor an appropriate receiver in a prescribed order: 1. It begins with the first responder in the key window and follows nextResponder links up the responder chain to the window object’s (NSWindow or UIWindow) content view. 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 73 Target-ActionNote: A key window in OS X responds to key presses for an application and is the receiver of messages from menus and dialogs. An application’s main window is the principal focus of user actions and often has key status as well. 2. It tries the window object and then the window object’s delegate. 3. If the main window is different from the key window, it then starts over with the first responder in the main window and works its way up the main window’s responder chain to the window object and its delegate. 4. Next, the application object tries to respond. If it can’t respond, it tries its delegate. The application object and its delegate are the receivers of last resort. Control objects do not (and should not) retain their targets. However, clients of controlssending action messages (applications, usually) are responsible for ensuring that their targets are available to receive action messages. To do this, they may have to retain their targets in memory-managed environments. This precaution applies equally to delegates and data sources. The Action An action is the message a control sends to the target or, from the perspective of the target, the method the target implements to respond to the action message. A control or—as is frequently the case in AppKit—a control’s cell stores an action as an instance variable of type SEL. SEL is an Objective-C data type used to specify the signature of a message. An action message must have a simple, distinct signature. The method it invokes returns nothing and usually has a sole parameter of type id. This parameter, by convention, is named sender. Here is an example from the NSResponder class, which defines a number of action methods: - (void)capitalizeWord:(id)sender; Action methods declared by some Cocoa classes can also have the equivalent signature: - (IBAction) deleteRecord:(id)sender; In this case, IBAction does not designate a data type for a return value; no value is returned. IBAction is a type qualifier that Interface Builder notices during application development to synchronize actions added programmatically with its internal list of action methods defined for a project. Target-Action The Action 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 74iOS Note: In UIKit, action selectors can also take two other forms. See “Target-Action in UIKit” (page 78) for details. The senderparameter usually identifies the control sending the action message (although it can be another object substituted by the actual sender). The idea behind this is similar to a return address on a postcard. The target can query the sender for more information if it needsto. If the actualsending objectsubstitutes another object as sender, you should treat that object in the same way. For example, say you have a text field and when the user enters text, the action method nameEntered: is invoked in the target: - (void)nameEntered:(id) sender { NSString *name = [sender stringValue]; if (![name isEqualToString:@""]) { NSMutableArray *names = [self nameList]; [names addObject:name]; [sender setStringValue:@""]; } } Here the responding method extracts the contents of the text field, adds the string to an array cached as an instance variable, and clears the field. Other possible queries to the sender would be asking an NSMatrix object for its selected row ([sender selectedRow]), asking an NSButton object for its state ([sender state]), and asking any cell associated with a control for its tag ([[sender cell] tag]), a tag being a numeric identifier. Target-Action in the AppKit Framework The AppKit framework uses specific architectures and conventions in implementing target-action. Controls, Cells, and Menu Items Most controls in AppKit are objects that inherit from the NSControl class. Although a control has the initial responsibility for sending an action message to its target, it rarely carries the information needed to send the message. For this, it usually relies on its cell or cells. A control almost always has one or more cells—objects that inherit from NSCell—associated with it. Why is there this association? A control is a relatively “heavy” object because it inherits all the combined instance variables of its ancestors, which include the NSView and NSResponder classes. Because controls are expensive, Target-Action Target-Action in the AppKit Framework 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 75cells are used to subdivide the screen real estate of a control into various functional areas. Cells are lightweight objects that can be thought of as overlaying all or part of the control. But it's not only a division of area, it's a division of labor. Cells do some of the drawing that controls would otherwise have to do, and cells hold some of the data that controls would otherwise have to carry. Two items of this data are the instance variables for target and action. Figure 12-1 (page 76) depicts the control-cell architecture. Being abstract classes, NSControl and NSCell both incompletely handle the setting of the target and action instance variables. By default, NSControl simply sets the information in its associated cell, if one exists. (NSControl itself supports only a one-to-one mapping between itself and a cell; subclasses of NSControl such as NSMatrix support multiple cells.) In its default implementation, NSCell simply raises an exception. You must go one step further down the inheritance chain to find the class that really implements the setting of target and action: NSActionCell. Objects derived from NSActionCell provide target and action values to their controls so the controls can compose and send an action message to the proper receiver. An NSActionCell object handles mouse (cursor) tracking by highlighting its area and assisting its control in sending action messages to the specified target. In most cases, the responsibility for an NSControl object’s appearance and behavior is completely given over to a corresponding NSActionCell object. (NSMatrix, and itssubclass NSForm, are subclasses of NSControl that don’t follow this rule.) Figure 12-1 How the target-action mechanism works in the control-cell architecture washerObject dryerObject washerCell dryerCell Target Action Target Action Control (NSMatrix) Cells (NSButtonCell) (void)dryIt: (id)sender (void)washIt: (id)sender Target-Action Target-Action in the AppKit Framework 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 76When users choose an item from a menu, an action is sent to a target. Yet menus (NSMenu objects) and their items (NSMenuItem objects) are completely separate, in an architectural sense, from controls and cells. The NSMenuItem class implements the target-action mechanism for its own instances; an NSMenuItem object has both target and action instance variables (and related accessor methods) and sends the action message to the target when a user chooses it. Note: See Control and Cell Programming Topics for Cocoa and Application Menu and Pop-up List Programming Topics for more information about the control-cell architecture. Setting the Target and Action You can set the targets and actions of cells and controls programmatically or by using Interface Builder. For most developers and mostsituations, Interface Builder isthe preferred approach. When you use it to set controls and targets, Interface Builder provides visual confirmation, allows you to lock the connections, and archives the connections to a nib file. The procedure is simple: 1. Declare an action method in the header file of your custom class that has the IBAction qualifier. 2. In Interface Builder, connect the control sending the message to the action method of the target. If the action is handled by a superclass of your custom class or by an off-the-shelf AppKit or UIKit class, you can make the connection without declaring any action method. Of course, if you declare an action method yourself, you must be sure to implement it. To set the action and the target programmatically, use the following methods to send messages to a control or cell object: - (void)setTarget:(id)anObject; - (void)setAction:(SEL)aSelector; The following example shows how you might use these methods: [aCell setTarget:myController]; [aControl setAction:@selector(deleteRecord:)]; [aMenuItem setAction:@selector(showGuides:)]; Target-Action Target-Action in the AppKit Framework 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 77Programmatically setting the target and action does have its advantages and in certain situations it is the only possible approach. For example, you might want the target or action to vary according to some runtime condition, such as whether a network connection exists or whether an inspector window has been loaded. Another example is when you are dynamically populating the items of a pop-up menu, and you want each pop-up item to have its own action. Actions Defined by AppKit The AppKit framework not only includes many NSActionCell-based controls for sending action messages, it defines action methods in many of its classes. Some of these actions are connected to default targets when you create a Cocoa application project. For example, the Quit command in the application menu is connected to the terminate: method in the global application object (NSApp). The NSResponder class also defines many default action messages (also known as standard commands) for common operations on text. This allowsthe Cocoa textsystem to send these action messages up an application’s responder chain—a hierarchical sequence of event-handling objects—where it can be handled by the first NSView, NSWindow, or NSApplication object that implements the corresponding method. Target-Action in UIKit The UIKit framework also declares and implements a suite of control classes; the control classesin thisframework inherit from the UIControl class, which defines most of the target-action mechanism for iOS. However there are some fundamental differences in how the AppKit and UIKit frameworks implement target-action. One of these differences is that UIKit does not have any true cell classes. Controls in UIKit do not rely upon their cells for target and action information. A larger difference in how the two frameworks implement target-action lies in the nature of the event model. In the AppKit framework, the user typically uses a mouse and keyboard to register events for handling by the system. These events—such as clicking on a button—are limited and discrete. Consequently, a control object in AppKit usually recognizes a single physical event as the trigger for the action it sends to its target. (In the case of buttons, this is a mouse-up event.) In iOS, the user’s fingers are what originate events instead of mouse clicks, mouse drags, or physical keystrokes. There can be more than one finger touching an object on the screen at one time, and these touches can even be going in different directions. To account for this multitouch event model, UIKit declares a set of control-event constants in UIControl.h that specify various physical gestures that users can make on controls, such as lifting a finger from a control, dragging a finger into a control, and touching down within a text field. You can configure a control object so that it responds to one or more of these touch events by sending an action message to a target. Many of the Target-Action Target-Action in UIKit 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 78control classes in UIKit are implemented to generate certain control events; for example, instances of the UISlider class generate a UIControlEventValueChanged control event, which you can use to send an action message to a target object. You set up a control so that it sends an action message to a target object by associating both target and action with one or more control events. To do this, send addTarget:action:forControlEvents: to the control for each target-action pair you want to specify. When the user touches the control in a designated fashion, the control forwards the action message to the global UIApplication object in a sendAction:to:from:forEvent: message. As in AppKit, the global application object is the centralized dispatch point for action messages. If the control specifies a nil target for an action message, the application queries objects in the responder chain until it finds one that is willing to handle the action message—that is, one implementing a method corresponding to the action selector. In contrast to the AppKit framework, where an action method may have only one or perhapstwo valid signatures, the UIKit framework allows three different forms of action selector: - (void)action - (void)action:(id)sender - (void)action:(id)sender forEvent:(UIEvent *)event To learn more about the target-action mechanism in UIKit, read UIControl Class Reference . Target-Action Target-Action in UIKit 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 79There are a number of data types in the Core Foundation framework and the Foundation framework that can be used interchangeably. This capability, called toll-free bridging , means that you can use the same data type as the parameter to a Core Foundation function call or as the receiver of an Objective-C message. For example, NSLocale (see NSLocale Class Reference ) is interchangeable with its Core Foundation counterpart, CFLocale (see CFLocale Reference ). Therefore, in a method where you see an NSLocale * parameter, you can pass a CFLocaleRef, and in a function where you see a CFLocaleRef parameter, you can pass an NSLocale instance. You cast one type to the other to suppress compiler warnings, as illustrated in the following example. NSLocale *gbNSLocale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_GB"]; CFLocaleRef gbCFLocale = (CFLocaleRef) gbNSLocale; CFStringRef cfIdentifier = CFLocaleGetIdentifier (gbCFLocale); NSLog(@"cfIdentifier: %@", (NSString *)cfIdentifier); // logs: "cfIdentifier: en_GB" CFRelease((CFLocaleRef) gbNSLocale); CFLocaleRef myCFLocale = CFLocaleCopyCurrent(); NSLocale * myNSLocale = (NSLocale *) myCFLocale; [myNSLocale autorelease]; NSString *nsIdentifier = [myNSLocale localeIdentifier]; CFShow((CFStringRef) [@"nsIdentifier: " stringByAppendingString:nsIdentifier]); // logs identifier for current locale Note from the example that the memory management functions and methods are also interchangeable—you can use CFRelease with a Cocoa object and release and autorelease with a Core Foundation object. 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 80 Toll-Free BridgingNote: When using garbage collection, there are important differencesto how memory management works for Cocoa objects and Core Foundation objects. See “Using Core Foundation with Garbage Collection” for details. Toll-free bridging has been available since OS X v10.0. Table 13-1 provides a list of the data types that are interchangeable between Core Foundation and Foundation. For each pair, the table also lists the version of OS X in which toll-free bridging between them became available. Table 13-1 Data types that can be used interchangeably between Core Foundation and Foundation Core Foundation type Foundation class Availability CFArrayRef NSArray OS X v10.0 CFAttributedStringRef NSAttributedString OS X v10.4 CFCalendarRef NSCalendar OS X v10.4 CFCharacterSetRef NSCharacterSet OS X v10.0 CFDataRef NSData OS X v10.0 CFDateRef NSDate OS X v10.0 CFDictionaryRef NSDictionary OS X v10.0 CFErrorRef NSError OS X v10.5 CFLocaleRef NSLocale OS X v10.4 CFMutableArrayRef NSMutableArray OS X v10.0 CFMutableAttributedStringRef NSMutableAttributedString OS X v10.4 CFMutableCharacterSetRef NSMutableCharacterSet OS X v10.0 CFMutableDataRef NSMutableData OS X v10.0 CFMutableDictionaryRef NSMutableDictionary OS X v10.0 CFMutableSetRef NSMutableSet OS X v10.0 CFMutableStringRef NSMutableString OS X v10.0 CFNumberRef NSNumber OS X v10.0 CFReadStreamRef NSInputStream OS X v10.0 Toll-Free Bridging 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 81Core Foundation type Foundation class Availability CFRunLoopTimerRef NSTimer OS X v10.0 CFSetRef NSSet OS X v10.0 CFStringRef NSString OS X v10.0 CFTimeZoneRef NSTimeZone OS X v10.0 CFURLRef NSURL OS X v10.0 CFWriteStreamRef NSOutputStream OS X v10.0 Note: Not all data types are toll-free bridged, even though their names might suggest that they are. For example, NSRunLoop is not toll-free bridged to CFRunLoop, NSBundle is not toll-free bridged to CFBundle, and NSDateFormatter is not toll-free bridged to CFDateFormatter. Toll-Free Bridging 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 82This table describes the changes to Concepts in Objective-C Programming . Date Notes Descriptions of design patterns, architectures, and other concepts important in Cocoa and Cocoa Touch development. 2012-01-09 2012-01-09 | © 2012 Apple Inc. All Rights Reserved. 83 Document Revision HistoryApple Inc. © 2012 Apple Inc. All rights reserved. No part of this publication may be reproduced, stored in a retrievalsystem, or transmitted, in any form or by any means, mechanical, electronic, photocopying, recording, or otherwise, without prior written permission of Apple Inc., with the following exceptions: Any person is hereby authorized to store documentation on a single computer for personal use only and to print copies of documentation for personal use provided that the documentation contains Apple’s copyright notice. No licenses, express or implied, are granted with respect to any of the technology described in this document. Apple retains all intellectual property rights associated with the technology described in this document. This document is intended to assist application developers to develop applications only for Apple-labeled computers. Apple Inc. 1 Infinite Loop Cupertino, CA 95014 408-996-1010 Apple, the Apple logo, Cocoa, Cocoa Touch, Objective-C, OS X, and Xcode are trademarks of Apple Inc., registered in the U.S. and other countries. iOS is a trademark or registered trademark of Cisco in the U.S. and other countries and is used under license. Even though Apple has reviewed this document, APPLE MAKES NO WARRANTY OR REPRESENTATION, EITHER EXPRESS OR IMPLIED, WITH RESPECT TO THIS DOCUMENT, ITS QUALITY, ACCURACY, MERCHANTABILITY, OR FITNESS FOR A PARTICULAR PURPOSE.ASARESULT, THISDOCUMENT IS PROVIDED “AS IS,” AND YOU, THE READER, ARE ASSUMING THE ENTIRE RISK AS TO ITS QUALITY AND ACCURACY. IN NO EVENT WILL APPLE BE LIABLE FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL,OR CONSEQUENTIAL DAMAGES RESULTING FROM ANY DEFECT OR INACCURACY IN THIS DOCUMENT, even if advised of the possibility of such damages. THE WARRANTY AND REMEDIES SET FORTH ABOVE ARE EXCLUSIVE AND IN LIEU OF ALL OTHERS, ORAL OR WRITTEN, EXPRESS OR IMPLIED. 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Local and Push Notification Programming GuideContents About Local Notifications and Push Notifications 5 At a Glance 6 The Problem That Local and Push Notifications Solve 6 Local and Push Notifications Are Different in Origination 6 You Schedule a Local Notification, Register a Push Notification, and Handle Both 6 The Apple Push Notification Service Is the Gateway for Push Notifications 7 You Must Obtain Security Credentials for Push Notifications 7 The Provider Communicates with APNs over a Binary Interface 7 Prerequisites 8 See Also 8 Local and Push Notifications in Depth 9 Push and Local Notifications Appear the Same to Users 9 More About Local Notifications 12 More About Push Notifications 13 Scheduling, Registering, and Handling Notifications 15 Preparing Custom Alert Sounds 15 Scheduling Local Notifications 16 Registering for Remote Notifications 19 Handling Local and Remote Notifications 21 Passing the Provider the Current Language Preference (Remote Notifications) 26 Apple Push Notification Service 28 A Push Notification and Its Path 28 Feedback Service 29 Quality of Service 30 Security Architecture 30 Service-to-Device Connection Trust 31 Provider-to-Service Connection Trust 31 Token Generation and Dispersal 32 Token Trust (Notification) 34 Trust Components 34 The Notification Payload 35 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 2Localized Formatted Strings 37 Examples of JSON Payloads 39 Provisioning and Development 42 Sandbox and Production Environments 42 Provisioning Procedures 43 Creating the SSL Certificate and Keys 43 Creating and Installing the Provisioning Profile 44 Installing the SSL Certificate and Key on the Server 45 Provider Communication with Apple Push Notification Service 47 General Provider Requirements 47 The Binary Interface and Notification Formats 48 The Feedback Service 53 Document Revision History 55 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 3 ContentsFigures, Tables, and Listings Local and Push Notifications in Depth 9 Figure 1-1 A notification alert 10 Figure 1-2 An application icon with a badge number (iOS) 11 Figure 1-3 A notification alert message with the action button suppressed 11 Scheduling, Registering, and Handling Notifications 15 Listing 2-1 Creating, configuring, and scheduling a local notification 17 Listing 2-2 Presenting a local notification immediately while running in the background 18 Listing 2-3 Registering for remote notifications 21 Listing 2-4 Handling a local notification when an application is launched 23 Listing 2-5 Downloading data from a provider 24 Listing 2-6 Handling a local notification when an application is already running 25 Listing 2-7 Getting the current supported language and sending it to the provider 26 Apple Push Notification Service 28 Figure 3-1 A push notification from a provider to a client application 29 Figure 3-2 Push notifications from multiple providers to multiple devices 29 Figure 3-3 Sharing the device token 33 Table 3-1 Keys and values of the aps dictionary 36 Table 3-2 Child properties of the alert property 36 Provider Communication with Apple Push Notification Service 47 Figure 5-1 Simple notification format 49 Figure 5-2 Enhanced notification format 50 Figure 5-3 Format of error-response packet 51 Figure 5-4 Binary format of a feedback tuple 54 Table 5-1 Codes in error-response packet 51 Listing 5-1 Sending a notification in the simple format via the binary interface 49 Listing 5-2 Sending a notification in the enhanced format via the binary interface 52 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 4Local notifications and push notifications are ways for an application that isn’t running in the foreground to let its users know it has information for them. The information could be a message, an impending calendar event, or new data on a remote server. When presented by the operating system, local and push notifications look and sound the same. They can display an alert message or they can badge the application icon. They can also play a sound when the alert or badge number is shown. Push notifications were introduced in iOS 3.0 and in OS X version 10.7. Local notifications were introduced in iOS 4.0; they are not available in OS X. When users are notified that the application has a message, event, or other data for them, they can launch the application and see the details. They can also choose to ignore the notification, in which case the application is not activated. 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 5 About Local Notifications and Push NotificationsNote: Push notifications and local notifications are not related to broadcast notifications (NSNotificationCenter) or key-value observing notifications. At a Glance Local notifications and push notifications have several important aspects you should be aware of. The Problem That Local and Push Notifications Solve Only one application can be active in the foreground at any time. Many applications operate in a time-based or interconnected environment where events of interest to users can occur when the application is not in the foreground. Local and push notifications allow these applicationsto notify their users when these events occur. Relevant Chapter: “Local and Push Notifications in Depth” (page 9) Local and Push Notifications Are Different in Origination Local and push notifications serve different design needs. A local notification is local to an application on an iPhone, iPad, or iPod touch. Push notifications—also known as remote notifications—arrive from outside a device. They originate on a remote server—the application’s provider—and are pushed to applications on devices (via the Apple Push Notification service) when there are messages to see or data to download. Relevant Chapter: “Local and Push Notifications in Depth” (page 9) You Schedule a Local Notification, Register a Push Notification, and Handle Both To have iOS deliver a local notification at a later time, an application creates a UILocalNotification object, assignsit a delivery date and time,specifies presentation details, and schedulesit. To receive push notifications, an application must register to receive the notifications and then pass to its provider a device token it gets from the operating system. When the operating system delivers a local notification (iOS only) or push notification (iOS or OS X) and the target application is not running in the foreground, it presents the notification (alert, icon badge number, sound). If there is a notification alert and the user taps or clicks the action button (or moves the action slider), the application launches and calls a method to pass in the local-notification object or remote-notification payload. If the application is running in the foreground when the notification is delivered, the application delegate receives a local or push notification. About Local Notifications and Push Notifications At a Glance 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 6Relevant Chapter: “Scheduling, Registering, and Handling Notifications” (page 15) The Apple Push Notification Service Is the Gateway for Push Notifications Apple Push Notification service (APNs) propagates push notificationsto devices having applicationsregistered to receive those notifications. Each device establishes an accredited and encrypted IP connection with the service and receives notifications over this persistent connection. Providers connect with APNs through a persistent and secure channel while monitoring incoming data intended for their client applications. When new data for an application arrives, the provider prepares and sends a notification through the channel to APNs, which pushes the notification to the target device. Related Chapter: “Apple Push Notification Service” (page 28) You Must Obtain Security Credentials for Push Notifications To develop and deploy the provider side of an application for push notifications, you must get SSL certificates from the appropriate Dev Center. Each certificate is limited to a single application, identified by its bundle ID; it is also limited to one of two environments, sandbox (for development and testing) and production. These environments have their own assigned IP address and require their own certificates. You must also obtain provisioning profiles for each of these environments. Related Chapter: “Provisioning and Development” (page 42) The Provider Communicates with APNs over a Binary Interface The binary interface is asynchronous and uses a streaming TCP socket design for sending push notifications as binary content to APNs. There is a separate interface for the sandbox and production environments, each with its own address and port. For each interface, you need to use TLS (or SSL) and the SSL certificate you obtained to establish a secured communications channel. The provider composes each outgoing notification and sends it over this channel to APNs. APNs has a feedback service that maintains a per-application list of devicesfor which there were failed-delivery attempts (that is, APNs was unable to deliver a push notification to an application on a device). Periodically, the provider should connect with the feedback service to see what devices have persistent failures so that it can refrain from sending push notifications to them. About Local Notifications and Push Notifications At a Glance 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 7Related Chapters: “Apple Push Notification Service” (page 28), “Provider Communication with Apple Push Notification Service” (page 47) Prerequisites For local notifications and the client-side implementation of push notifications, familiarity with application development for iOS is assumed. For the provider side of the implementation, knowledge of TLS/SSL and streaming sockets is helpful. See Also You might find these additional sources of information useful for understanding and implementing local and push notifications : ● The reference documentation for UILocalNotification, UIApplication, and UIApplicationDelegate describe the local- and push-notification API for client applications in iOS. ● The reference documentation for NSApplication and NSApplicationDelegate Protocol describe the push-notification API for client applications in OS X. ● Security Overview describes the security technologies and techniques used for the iOS and Macs. ● RFC 5246 is the standard for the TLS protocol. Secure communication between data providers and Apple Push Notification Service requires knowledge of Transport Layer Security (TLS) or its predecessor, Secure Sockets Layer (SSL). Refer to one of the many online or printed descriptions of these cryptographic protocols for further information. About Local Notifications and Push Notifications Prerequisites 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 8The essential purpose of both local and push notifications is to enable an application to inform its users that it hassomething for them—for example, a message or an upcoming appointment—when the application isn’t running in the foreground. The essential difference between local notifications and push notificationsissimple: ● Local notifications are scheduled by an application and delivered by iOS on the same device. Local notifications are available in iOS only. ● Push notifications, also known as remote notifications, are sent by an application’s remote server (its provider) to Apple Push Notification service, which pushes the notification to devices on which the application is installed. Push notifications are available in both iOS and, beginning with OS X v10.7 (Lion), OS X. The following sections describe what local and push notifications have in common and then examine their differences. Note: For usage guidelines for push and local notifications in iOS, see “Enabling Push Notifications” in iOS Human Interface Guidelines. Push and Local Notifications Appear the Same to Users From a user’s perspective, a push notification and a local notification appear to be the same thing. But that’s because the purpose is the same: to notify users of an application—which might not currently be running in the foreground—that there is something of interest for them. Let’s say you’re using your iPhone—making phone calls, surfing the Internet, listening to music. You have a chess application installed on your iPhone, and you decide to start a game with a friend who is playing remotely. You make the first move (which is duly noted by the game’s provider), and then quit the client application to read some email. In the meantime, your friend counters your move. The provider for the chess application learns about this move and, seeing that the chess application on your device is no longer connected, sends a push notification to Apple Push Notification service (APNs). 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 9 Local and Push Notifications in DepthAlmost immediately, your device—or more precisely, the operating system on your device—receives the notification over the Wi-Fi or cellular connection from APNs. Because your chess application is not currently running, iOS displays an alert similar to Figure 1-1. The message consists of the application name, a short message, and (in this case) two buttons: Close and View. The button on the right is called the action button and its default title is“View”. An application can customize the title of the action button and can internationalize the button title and the message so that they are in the user’s preferred language. Figure 1-1 A notification alert If you tap the View button, the chess application launches, connects with its provider, downloads the new data, and adjuststhe chessboard user interface to show your friend’s move. (Pressing Close dismissesthe alert.) OS X Note: Currently, the only type of push notification in OS X for non-running applications is icon badging. In other words, an application’s icon in the Dock is badged only if the application isn’t running. If users have not already placed the icon in the Dock, the system inserts the icon into the Dock so that it can badge it (and removes it after the application next terminates). Running applications may examine the notification payload for other types of notifications(alerts and sounds) and handle them appropriately. Let’s consider a type of application with another requirement. This application manages a to-do list, and each item in the list has a date and time when the item must be completed. The user can request the application to notify it at a specific interval before this due date expires. To effect this, the application schedules a local notification for that date and time. Instead of specifying an alert message, this time the application chooses to specify a badge number (1). At the appointed time, iOS displays a badge number in the upper-right corner of the icon of the application, such as illustrated in Figure 1-2. Local and Push Notifications in Depth Push and Local Notifications Appear the Same to Users 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 10For both local and push notifications, the badge number is specific to an application and can indicate any number of things,such asthe number of impending calendar events or the number of data itemsto download or the number of unread (but already downloaded) email messages. The user sees the badge and taps the application icon—or, in OS X, clicks the icon in the dock—to launch the application, which then displays the to-do item or whatever else is of interest to the user. Figure 1-2 An application icon with a badge number (iOS) In iOS, an application can specify a sound file along with an alert message or badge number. The sound file should contain a short, distinctive sound. At the same moment iOS displays the alert or badges the icon, it plays the sound to alert the user to the incoming notification. Notification alert message can have one button instead of two. In the latter case, the action button issuppressed, as illustrated in Figure 1-3. The user can only dismiss these kinds of alerts. Figure 1-3 A notification alert message with the action button suppressed Local and Push Notifications in Depth Push and Local Notifications Appear the Same to Users 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 11The operating system delivers a local or push notification to an application whether the application is running or not. If the application is running when the notification arrives, no alert is displayed or icon badged or sound played, even if (in iOS) the device screen islocked. Instead, the application delegate isinformed of the notification and can handle it directly. (“Scheduling, Registering, and Handling Notifications” (page 15) discusses the various delivery scenarios in detail.) Users of iPhone, iPad, and iPod touch devices can control whether the device or specific applications installed on the device should receive push notifications. They can also selectively enable or disable push notification types (that is, icon badging, alert messages, and sounds) for specific applications. They set these restrictions in the Notifications preference of the Settings application. The UIKit framework provides a programming interface to detect this user preference for a given application. More About Local Notifications Local notifications(available only in iOS) are ideally suited for applications with time-based behaviors, including simple calendar or to-do list applications. Applicationsthat run in the background for the limited period allowed by iOS might also find local notifications useful. For example, applicationsthat depend on serversfor messages or data can poll their servers for incoming items while running in the background; if a message is ready to view or an update is ready to download, they can then present a local notification immediately to inform their users. A local notification is an instance of UILocalNotification with three general kinds of properties: ● Scheduled time. You must specify the date and time the operating system delivers the notification; this is known as the fire date . You may qualify the fire date with a specific time zone so that the system can make adjustments to the fire date when the user travels. You can also request the operating system to reschedule the notification on some regular interval (weekly, monthly, and so on). ● Notification type. This category includes the alert message, the title of the action button, the application icon badge number, and a sound to play. ● Custom data. Local notifications can include a dictionary of custom data. “Scheduling Local Notifications” (page 16) describesthese propertiesin programmatic detail.Once an application has created a local-notification object, it can either schedule it with the operating system or present it immediately. Each application on a device is limited to the soonest-firing 64 scheduled local notifications. The operating system discards notificationsthat exceed thislimit. It considers a recurring notification to be a single notification. Local and Push Notifications in Depth More About Local Notifications 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 12More About Push Notifications An iOS application or a Mac app is often only a part of a larger application based on the client/server model. The client side of the application is installed on the device or computer; the server side of the application has the main function of providing data to its many client applications. (Hence it is termed a provider.) A client application occasionally connects with its provider and downloads the data that is waiting for it. Email and social-networking applications are examples of this client/server model. But what if the application is not connected to its provider or even running on the device or computer when the provider has new data for it to download? How does it learn about this waiting data? Push notifications are the solution to this dilemma. A push notification is a short message that a provider has delivered to the operating system of a device or computer; the operating system, in turn, informsthe user of a client application that there is data to be downloaded, a message to be viewed, and so on. If the user enables this feature (on iOS) and the application is properly registered, the notification is delivered to the operating system and possibly to the application. Apple Push Notification service is the primary technology for the push-notification feature. Push notificationsserve much the same purpose as a background application on a desktop system, but without the additional overhead. For an application that is not currently running—or, in the case of iOS, not running in the foreground—the notification occurs indirectly. The operating system receives a push notification on behalf of the application and alerts the user. Once alerted, users may choose to launch the application, which then downloads the data from its provider. If an application is running when a notification comes in, the application can choose to handle the notification directly. iOS Note: Beginning with iOS 4.0, applications can run in the background, but only for a limited period. Only one application may be executing in the foreground at a time. As its name suggests, Apple Push Notification service (APNs) uses a push design to deliver notifications to devices and computers. A push design differs from its opposite, a pull design, in that the immediate recipient of the notification—in this case, the operating system—passively listensfor updatesrather than actively polling for them. A push design makes possible a wide and timely dissemination of information with few of the scalability problems inherent with pull designs. APNs uses a persistent IP connection for implementing push notifications. Most of a push notification consists of a payload: a property list containing APNs-defined propertiesspecifying how the user is to be notified. For performance reasons, the payload is deliberately small. Although you may define custom properties for the payload, you should never use the remote-notification mechanism for data transport because delivery of push notificationsis not guaranteed. For more on the payload,see “The Notification Payload” (page 35). Local and Push Notifications in Depth More About Push Notifications 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 13APNs retains the last notification it receives from a provider for an application on a device; so, if a device or computer comes online and has not received the notification, APNs pushes the stored notification to it. A device running iOS receives push notifications over both Wi-Fi and cellular connections; a computer running OS X receives push notifications over both WiFi and Ethernet connections. Important: In iOS, Wi-Fi is used for push notifications only if there is no cellular connection or if the device is an iPod touch. For some devices to receive notifications via Wi-Fi, the device’s display must be on (that is, it cannot be sleeping) or it must be plugged in. The iPad, on the other hand, remains associated with the Wi-Fi access point while asleep, thus permitting the delivery of push notifications. The Wi-Fi radio wakes the host processor for any incoming traffic. Adding the remote-notification feature to your application requires that you obtain the proper certificates from the Dev Center for either iOS or OS X and then write the requisite code for the client and provider sides of the application. “Provisioning and Development” (page 42) explains the provisioning and setup steps, and “Provider Communication with Apple Push Notification Service” (page 47) and “Scheduling, Registering, and Handling Notifications” (page 15) describe the details of implementation. Apple Push Notification service continually monitors providersfor irregular behavior, looking forsudden spikes of activity, rapid connect-disconnect cycles, and similar activity. Apple seeksto notify providers when it detects this behavior, and if the behavior continues, it may put the provider’s certificate on a revocation list and refuse further connections. Any continued irregular or problematic behavior may result in the termination of a provider's access to APNs. Local and Push Notifications in Depth More About Push Notifications 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 14This chapter describes the tasks that a iPhone, iPad, or iPod touch application should (or might) do to schedule local notifications, register remote notifications, and handle both local and remote notifications. Because the client-side API for push notifications refers to push notifications as remote notifications, that terminology is used in this chapter. Preparing Custom Alert Sounds For remote notifications in iOS, you can specify a custom sound that iOS plays when it presents a local or remote notification for an application. The sound files must be in the main bundle of the client application. Because custom alert sounds are played by the iOS system-sound facility, they must be in one of the following audio data formats: ● Linear PCM ● MA4 (IMA/ADPCM) ● µLaw ● aLaw You can package the audio data in an aiff, wav, or caf file. Then, in Xcode, add the sound file to your project as a nonlocalized resource of the application bundle. You may use the afconvert tool to convert sounds. For example, to convert the 16-bit linear PCM system sound Submarine.aiff to IMA4 audio in a CAF file, use the following command in the Terminal application: afconvert /System/Library/Sounds/Submarine.aiff ~/Desktop/sub.caf -d ima4 -f caff -v You can inspect a sound to determine its data format by opening it in QuickTime Player and choosing Show Movie Inspector from the Movie menu. Custom sounds must be under 30 seconds when played. If a custom sound is over that limit, the defaultsystem sound is played instead. 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 15 Scheduling, Registering, and Handling NotificationsScheduling Local Notifications Creating and scheduling local notifications in iOS requires that you perform a few simple steps: 1. Allocate and initialize a UILocalNotification object. 2. Set the date and time that the operating system should deliver the notification. This is the fireDate property. If you set the timeZone property to the NSTimeZone object for the current locale, the system automatically adjusts the fire date when the device travels across (and is reset for) different time zones. (Time zones affect the values of date components—that is, day, month, hour, year, and minute—that the system calculates for a given calendar and date value.) You can also schedule the notification for delivery on a recurring basis (daily, weekly, monthly, and so on). 3. Configure the substance of the notification: alert, icon badge number, and sound. ● The alert has a property for the message (the alertBody property) and for the title of the action button or slider (alertAction); both of these string values can be internationalized for the user’s current language preference. ● You set the badge number to display on the application icon through the applicationIconBadgeNumber property. ● You can assign the filename of a nonlocalized custom sound in the application’s main bundle to the soundName property; to get the default system sound, assign UILocalNotificationDefaultSoundName. Sounds should always accompany an alert message or icon badging; they should not be played otherwise. 4. Optionally, you can attach custom data to the notification through the userInfo property. Keys and values in the userInfo dictionary must be property-list objects. 5. Schedule the local notification for delivery. You schedule a local notification by calling the UIApplicationmethod scheduleLocalNotification:. The application uses the fire date specified in the UILocalNotification object for the moment of delivery. Alternatively, you can present the notification immediately by calling the presentLocalNotificationNow: method. The method in Listing 2-1 creates and schedules a notification to inform the user of a hypothetical to-do list application about the impending due date of a to-do item. There are a couple things to note about it. For the alertBody and alertAction properties, it fetches from the main bundle (via the NSLocalizedString macro) strings localized to the user’s preferred language. It also adds the name of the relevant to-do item to a dictionary assigned to the userInfo property. Scheduling, Registering, and Handling Notifications Scheduling Local Notifications 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 16Listing 2-1 Creating, configuring, and scheduling a local notification - (void)scheduleNotificationWithItem:(ToDoItem *)item interval:(int)minutesBefore { NSCalendar *calendar = [NSCalendar autoupdatingCurrentCalendar]; NSDateComponents *dateComps = [[NSDateComponents alloc] init]; [dateComps setDay:item.day]; [dateComps setMonth:item.month]; [dateComps setYear:item.year]; [dateComps setHour:item.hour]; [dateComps setMinute:item.minute]; NSDate *itemDate = [calendar dateFromComponents:dateComps]; [dateComps release]; UILocalNotification *localNotif = [[UILocalNotification alloc] init]; if (localNotif == nil) return; localNotif.fireDate = [itemDate addTimeInterval:-(minutesBefore*60)]; localNotif.timeZone = [NSTimeZone defaultTimeZone]; localNotif.alertBody = [NSString stringWithFormat:NSLocalizedString(@"%@ in %i minutes.", nil), item.eventName, minutesBefore]; localNotif.alertAction = NSLocalizedString(@"View Details", nil); localNotif.soundName = UILocalNotificationDefaultSoundName; localNotif.applicationIconBadgeNumber = 1; NSDictionary *infoDict = [NSDictionary dictionaryWithObject:item.eventName forKey:ToDoItemKey]; localNotif.userInfo = infoDict; [[UIApplication sharedApplication] scheduleLocalNotification:localNotif]; [localNotif release]; } Scheduling, Registering, and Handling Notifications Scheduling Local Notifications 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 17You can cancel a specific scheduled notification by calling cancelLocalNotification: on the application object, and you can cancel all scheduled notifications by calling cancelAllLocalNotifications. Both of these methods also programmatically dismiss a currently displayed notification alert. Applications might also find local notifications useful when they run in the background and some message, data, or other item arrivesthat might be of interest to the user. In this case, they should present the notification immediately using the UIApplication method presentLocalNotificationNow: (iOS gives an application a limited time to run in the background). Listing 2-2 illustrates how you might do this. Listing 2-2 Presenting a local notification immediately while running in the background - (void)applicationDidEnterBackground:(UIApplication *)application { NSLog(@"Application entered background state."); // bgTask is instance variable NSAssert(self->bgTask == UIInvalidBackgroundTask, nil); bgTask = [application beginBackgroundTaskWithExpirationHandler: ^{ dispatch_async(dispatch_get_main_queue(), ^{ [application endBackgroundTask:self->bgTask]; self->bgTask = UIInvalidBackgroundTask; }); }]; dispatch_async(dispatch_get_main_queue(), ^{ while ([application backgroundTimeRemaining] > 1.0) { NSString *friend = [self checkForIncomingChat]; if (friend) { UILocalNotification *localNotif = [[UILocalNotification alloc] init]; if (localNotif) { localNotif.alertBody = [NSString stringWithFormat: NSLocalizedString(@"%@ has a message for you.", nil), friend]; localNotif.alertAction = NSLocalizedString(@"Read Message", nil); localNotif.soundName = @"alarmsound.caf"; localNotif.applicationIconBadgeNumber = 1; [application presentLocalNotificationNow:localNotif]; Scheduling, Registering, and Handling Notifications Scheduling Local Notifications 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 18[localNotif release]; friend = nil; break; } } } [application endBackgroundTask:self->bgTask]; self->bgTask = UIInvalidBackgroundTask; }); } Registering for Remote Notifications An application must register with Apple Push Notification service for the operating systems on a device and on a computer to receive remote notifications sent by the application’s provider. Registration has three stages: 1. The application calls the registerForRemoteNotificationTypes: method. 2. The delegate implements the application:didRegisterForRemoteNotificationsWithDeviceToken: method to receive the device token. 3. It passes the device token to its provider as a non-object, binary value. Note: Unless otherwise noted, all methods cited in thissection are declared with identicalsignatures by both UIApplication and NSApplication, and, for delegates, by both NSApplicationDelegate Protocol and UIApplicationDelegate. What happens between the application, the device, Apple Push Notification Service, and the provider during this sequence is illustrated by Figure 3-3 in “Token Generation and Dispersal” (page 32). An application should register every time it launches and give its provider the current token. It calls theregisterForRemoteNotificationTypes: method to kick off the registration process. The parameter of this method takes a UIRemoteNotificationType (or, for OS X, a NSRemoteNotificationType) bit mask that specifies the initial types of notifications that the application wishes to receive—for example, icon-badging and sounds, but not alert messages. In iOS, users can thereafter modify the enabled notification types in the Notifications preference of the Settings application. In both iOS and OS X, you can retrieve the Scheduling, Registering, and Handling Notifications Registering for Remote Notifications 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 19currently enabled notification types by calling the enabledRemoteNotificationTypes method. The operating system does not badge icons, display alert messages, or play alertsoundsif any of these notifications types are not enabled, even if they are specified in the notification payload. OS XNote: Because the only notification type supported for non-running applicationsisicon-badging, simply pass NSRemoteNotificationTypeBadge as the parameter of registerForRemoteNotificationTypes:. If registration issuccessful, APNsreturns a device token to the device and iOS passesthe token to the application delegate in the application:didRegisterForRemoteNotificationsWithDeviceToken: method. The application should connect with its provider and pass it this token, encoded in binary format. If there is a problem in obtaining the token, the operating system informs the delegate by calling the application:didFailToRegisterForRemoteNotificationsWithError:method. The NSError object passed into this method clearly describes the cause of the error. The error might be, for instance, an erroneous aps-environment value in the provisioning profile. You should view the error as a transient state and not attempt to parse it. (See “Creating and Installing the Provisioning Profile” (page 44) for details.) iOS Note: If a cellular or Wi-Fi connection is not available, neither the application:didRegisterForRemoteNotificationsWithDeviceToken: method or the application:didFailToRegisterForRemoteNotificationsWithError: method is called. For Wi-Fi connections, this sometimes occurs when the device cannot connect with APNs over port 5223. If this happens, the user can move to another Wi-Fi network that isn’t blocking this port or, on an iPhone or iPad, wait until the cellular data service becomes available. In either case, the connection should then succeed and one of the delegation methods is called. By requesting the device token and passing it to the provider every time your application launches, you help to ensure that the provider has the current token for the device. If a user restores a backup to a device or computer other than the one that the backup was created for (for example, the user migrates data to a new device or computer), he or she must launch the application at least once for it to receive notifications again. If the user restores backup data to a new device or computer, or reinstalls the operating system, the device token changes. Moreover, never cache a device token and give that to your provider; always get the token from the system whenever you need it. If your application has previously registered, calling registerForRemoteNotificationTypes: resultsin the operating system passing the device token to the delegate immediately without incurring additional overhead. Listing 2-3 gives a simple example of how you might register for remote notifications in an iOS application. The code would be nearly identical for a Mac app. (SendProviderDeviceToken is a hypothetical method defined by the client in which it connects with its provider and passes it the device token.) Scheduling, Registering, and Handling Notifications Registering for Remote Notifications 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 20Listing 2-3 Registering for remote notifications - (void)applicationDidFinishLaunching:(UIApplication *)app { // other setup tasks here.... [[UIApplication sharedApplication] registerForRemoteNotificationTypes:(UIRemoteNotificationTypeBadge | UIRemoteNotificationTypeSound)]; } // Delegation methods - (void)application:(UIApplication *)app didRegisterForRemoteNotificationsWithDeviceToken:(NSData *)devToken { const void *devTokenBytes = [devToken bytes]; self.registered = YES; [self sendProviderDeviceToken:devTokenBytes]; // custom method } - (void)application:(UIApplication *)app didFailToRegisterForRemoteNotificationsWithError:(NSError *)err { NSLog(@"Error in registration. Error: %@", err); } Handling Local and Remote Notifications Let’s review the possible scenarios when the operating delivers a local notification or a remote notification for an application. ● The notification is delivered when the application isn’t running in the foreground. In this case, the system presents the notification, displaying an alert, badging an icon, perhaps playing a sound. ● As a result of the presented notification, the user taps the action button of the alert or taps (or clicks) the application icon. If the action button is tapped (on a device running iOS), the system launches the application and the application calls its delegate’s application:didFinishLaunchingWithOptions: method (if implemented); it passesin the notification payload (for remote notifications) or the local-notification object (for local notifications). Scheduling, Registering, and Handling Notifications Handling Local and Remote Notifications 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 21If the application icon is tapped on a device running iOS, the application calls the same method, but furnishes no information about the notification . If the application icon is clicked on a computer running OS X, the application calls the delegate’s applicationDidFinishLaunching: method in which the delegate can obtain the remote-notification payload. iOS Note: The application delegate could implement applicationDidFinishLaunching: rather than application:didFinishLaunchingWithOptions:, but that is strongly discouraged. The latter method allows the application to receive information related to the reason for its launching, which can include things other than notifications. ● The notification is delivered when the application is running in the foreground. The application calls its delegate’s application:didReceiveRemoteNotification: method (for remote notifications) or application:didReceiveLocalNotification:method (forlocal notifications) and passes in the notification payload or the local-notification object. Note: The delegate methods cited in this section that have “RemoteNotification” in their name are declared with identical signatures by by both NSApplicationDelegate Protocol and UIApplicationDelegate. An application can use the passed-in remote-notification payload or, in iOS, the UILocalNotification object to help set the context for processing the item related to the notification. Ideally, the delegate does the following on each platform to handle the delivery of remote and local notifications in all situations: ● For OS X, it should adopt the NSApplicationDelegate Protocol protocol and implement both the applicationDidFinishLaunching: method and the application:didReceiveRemoteNotification: method. ● For iOS, it should should adopt the UIApplicationDelegate protocol and implement both the application:didFinishLaunchingWithOptions: method and the application:didReceiveRemoteNotification: or application:didReceiveLocalNotification: method. Scheduling, Registering, and Handling Notifications Handling Local and Remote Notifications 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 22iOS Note: In iOS, you can determine whether an application is launched as a result of the user tapping the action button or whether the notification was delivered to the already-running application by examining the application state. In the delegate’s implementation of the application:didReceiveRemoteNotification: or application:didReceiveLocalNotification: method, get the value of the applicationState property and evaluate it. If the value is UIApplicationStateInactive, the user tapped the action button; if the value is UIApplicationStateActive, the application was frontmost when it received the notification. The delegate for an iOS application in Listing 2-4 implements the application:didFinishLaunchingWithOptions: method to handle a local notification. It gets the associated UILocalNotification object from the launch-options dictionary using the UIApplicationLaunchOptionsLocalNotificationKey key. From the UILocalNotification object’s userInfo dictionary, it accesses the to-do item that is the reason for the notification and uses it to set the application’s initial context. As shown in this example, you should appropriately reset the badge number on the application icon—or remove it if there are no outstanding items—as part of handling the notification. Listing 2-4 Handling a local notification when an application is launched - (BOOL)application:(UIApplication *)app didFinishLaunchingWithOptions:(NSDictionary *)launchOptions { UILocalNotification *localNotif = [launchOptions objectForKey:UIApplicationLaunchOptionsLocalNotificationKey]; if (localNotif) { NSString *itemName = [localNotif.userInfo objectForKey:ToDoItemKey]; [viewController displayItem:itemName]; // custom method application.applicationIconBadgeNumber = localNotif.applicationIconBadgeNumber-1; } [window addSubview:viewController.view]; [window makeKeyAndVisible]; return YES; } The implementation for a remote notification would be similar, except that you would use a specially declared constant in each platform as a key to access the notification payload: Scheduling, Registering, and Handling Notifications Handling Local and Remote Notifications 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 23● In iOS, the delegate, in its implementation of the application:didFinishLaunchingWithOptions: method, usesthe UIApplicationLaunchOptionsRemoteNotificationKey key to accessthe payload from the launch-options dictionary. ● In OS X, the delegate, in its implementation of the applicationDidFinishLaunching: method, uses the the NSApplicationLaunchRemoteNotificationKey key to access the payload dictionary from the userInfo dictionary of the NSNotification object that is passed into the method. The payload itself is an NSDictionary object that contains the elements of the notification—alert message, badge number, sound, and so on. It can also contain custom data the application can use to provide context when setting up the initial user interface. See “The Notification Payload” (page 35) for details about the remote-notification payload. Important: You should never define custom properties in the notification payload for the purpose of transporting customer data or any other sensitive data. Delivery of remote notifications is not guaranteed. One example of an appropriate usage for a custom payload property is a string identifying an email account from which messages are downloaded to an email client; the application can incorporate this string in its download user-interface. Another example of custom payload property is a timestamp for when the provider first sent the notification; the client application can use this value to gauge how old the notification is. When handling remote notifications in application:didFinishLaunchingWithOptions: or applicationDidFinishLaunching:, the application delegate might perform a major additional task. Just after the application launches, the delegate should connect with its provider and fetch the waiting data. Listing 2-5 gives a schematic illustration of this procedure. Listing 2-5 Downloading data from a provider - (void)application:(UIApplication *)app didFinishLaunchingWithOptions:(NSDictionary *)opts { // check launchOptions for notification payload and custom data, set UI context [self startDownloadingDataFromProvider]; // custom method app.applicationIconBadgeNumber = 0; // other setup tasks here.... } Scheduling, Registering, and Handling Notifications Handling Local and Remote Notifications 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 24Note: A client application should always communicate with its provider asynchronously or on a secondary thread. The code in Listing 2-6 shows an implementation of the application:didReceiveLocalNotification: method which, as you’ll recall, is called when application is running in the foreground. Here the application delegate doesthe same work asit doesin Listing 2-4. It can accessthe UILocalNotification object directly this time because this object is an argument of the method. Listing 2-6 Handling a local notification when an application is already running - (void)application:(UIApplication *)app didReceiveLocalNotification:(UILocalNotification *)notif { NSString *itemName = [notif.userInfo objectForKey:ToDoItemKey] [viewController displayItem:itemName]; // custom method application.applicationIconBadgeNumber = notification.applicationIconBadgeNumber-1; } If you want your application to catch remote notifications that the system delivers while it is running in the foreground, the application delegate should implement the application:didReceiveRemoteNotification: method. The delegate should begin the procedure for downloading the waiting data, message, or other item and, after this concludes, it should remove the badge from the application icon. (If your application frequently checks with its provider for new data, implementing this method might not be necessary.) The dictionary passed in the second parameter of this method is the notification payload; you should not use any custom properties it contains to alter your application’s current context. Even though the only supported notification type for nonrunning applications in OS X is icon-badging, the delegate can implement application:didReceiveRemoteNotification: to examine the notification payload for other types of notifications and handle them appropriately (that is, display an alert or play a sound). Scheduling, Registering, and Handling Notifications Handling Local and Remote Notifications 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 25iOS Note: If the user unlocks the device shortly after a remote-notification alert is displayed, the operating system automatically triggers the action associated with the alert. (This behavior is consistent with SMS and calendar alerts.) This makes it even more important that actions related to remote notifications do not have destructive consequences. A user should always make decisions that result in the destruction of data in the context of the application that stores the data. Passing the Provider the Current Language Preference (Remote Notifications) If an application doesn’t use the loc-key and loc-args properties of the aps dictionary for client-side fetching of localized alert messages, the provider needs to localize the text of alert messages it puts in the notification payload. To do this, however, the provider needs to know the language that the device user has selected as the preferred language. (The user sets this preference in the General > International > Language view of the Settings application.) The client application should send its provider an identifier of the preferred language; this could be a canonicalized IETF BCP 47 language identifier such as “en” or “fr”. Note: For more information about the loc-key and loc-args properties and client-side message localizations, see “The Notification Payload” (page 35). Listing 2-7 illustrates a technique for obtaining the currently selected language and communicating it to the provider. In iOS, the array returned by the preferredLanguages of NSLocale contains one object: an NSString object encapsulating the language code identifying the preferred language. The UTF8String coverts the string object to a C string encoded as UTF8. Listing 2-7 Getting the current supported language and sending it to the provider NSString *preferredLang = [[NSLocale preferredLanguages] objectAtIndex:0]; const char *langStr = [preferredLang UTF8String]; [self sendProviderCurrentLanguage:langStr]; // custom method } The application might send its provider the preferred language every time the user changes something in the current locale. To do this, you can listen for the notification named NSCurrentLocaleDidChangeNotification and, in your notification-handling method, get the code identifying the preferred language and send that to your provider. Scheduling, Registering, and Handling Notifications Passing the Provider the Current Language Preference (Remote Notifications) 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 26If the preferred language is not one the application supports, the provider should localize the message text in a widely spoken fallback language such as English or Spanish. Scheduling, Registering, and Handling Notifications Passing the Provider the Current Language Preference (Remote Notifications) 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 27Apple Push Notification service (APNsforshort) isthe centerpiece of the push notificationsfeature. It is a robust and highly efficientservice for propagating information to devicessuch asiPhone, iPad, and iPod touch devices. Each device establishes an accredited and encrypted IP connection with the service and receives notifications over this persistent connection. If a notification for an application arrives when that application is not running, the device alerts the user that the application has data waiting for it. Software developers (“providers”) originate the notifications in their server software. The provider connects with APNs through a persistent and secure channel while monitoring incoming data intended for their client applications. When new data for an application arrives, the provider prepares and sends a notification through the channel to APNs, which pushes the notification to the target device. In addition to being a simple but efficient and high-capacity transport service, APNs includes a default quality-of-service component that provides store-and-forward capabilities. See “Quality of Service” (page 30) for more information. “Provider Communication with Apple Push Notification Service” (page 47) and “Scheduling, Registering, and Handling Notifications” (page 15) discuss the specific implementation requirements for providers and iOS applications, respectively. A Push Notification and Its Path Apple Push Notification service transports and routes a notification from a given provider to a given device. A notification is a short message consisting of two major pieces of data: the device token and the payload. The device token is analogous to a phone number; it contains information that enables APNs to locate the device on which the client application is installed. APNs also uses it to authenticate the routing of a notification. The payload is a JSON-defined property list thatspecifies how the user of an application on a device isto be alerted. Note: For more information about the device token,see “Security Architecture” (page 30); for further information about the notification payload, see “The Notification Payload” (page 35) . The flow of remote-notification data is one-way. The provider composes a notification package that includes the device token for a client application and the payload. The provider sends the notification to APNs which in turn pushes the notification to the device. 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 28 Apple Push Notification ServiceWhen it authenticates itself to APNs, a provider furnishes the service with its topic, which identifies the application for which it’s providing data. The topic is currently the bundle identifier of the target application on an iOS device. Figure 3-1 A push notification from a provider to a client application Provider APNS notification notification Client App iPhone notification Figure 3-1 is a greatly simplified depiction of the virtual network APNs makes possible among providers and devices. The device-facing and provider-facing sides of APNs both have multiple points of connection; on the provider-facing side, these are called gateways. There are typically multiple providers, each making one or more persistent and secure connections with APNs through these gateways. And these providers are sending notifications through APNs to many devices on which their client applications are installed. Figure 3-2 is a slightly more realistic depiction. Figure 3-2 Push notifications from multiple providers to multiple devices APNS Provider B Provider A Feedback Service Sometimes APNs might attempt to deliver notifications for an application on a device, but the device may repeatedly refuse delivery because there is no target application. This often happens when the user has uninstalled the application. In these cases, APNs informs the provider through a feedback service that the provider connects with. The feedback service maintains a list of devices per application for which there were recent, repeated failed attempts to deliver notifications. The provider should obtain this list of devices and stop sending notifications to them. For more on this service, see “The Feedback Service” (page 53). Apple Push Notification Service Feedback Service 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 29Quality of Service Apple Push Notification Service includes a default Quality of Service (QoS) component that performs a store-and-forward function. If APNs attempts to deliver a notification but the device is offline, the QoS stores the notification. It retains only one notification per application on a device: the last notification received from a provider for that application. When the offline device later reconnects, the QoS forwardsthe stored notification to the device. The QoS retains a notification for a limited period before deleting it. Security Architecture To enable communication between a provider and a device, Apple Push Notification Service must expose certain entry points to them. But then to ensure security, it must also regulate access to these entry points. For this purpose, APNs requires two different levels of trust for providers, devices, and their communications. These are known as connection trust and token trust. Connection trust establishes certainty that, on one side, the APNs connection is with an authorized provider with whom Apple has agreed to deliver notifications. At the device side of the connection, APNs must validate that the connection is with a legitimate device. After APNs has established trust at the entry points, it must then ensure that it conveys notificationsto legitimate end points only. To do this, it must validate the routing of messages traveling through the transport; only the device that is the intended target of a notification should receive it. In APNs, assurance of accurate message routing—or token trust—is made possible through the device token. A device token is an opaque identifier of a device that APNs gives to the device when it first connects with it. The device shares the device token with its provider. Thereafter, this token accompanies each notification from the provider. It is the basis for establishing trust that the routing of a particular notification is legitimate. (In a metaphorical sense, it has the same function as a phone number, identifying the destination of a communication.) Note: A device token is not the same thing asthe device UDID returned by the uniqueIdentifier property of UIDevice. The following sections discuss the requisite components for connection trust and token trust as well as the four procedures for establishing trust. Apple Push Notification Service Quality of Service 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 30Service-to-Device Connection Trust APNs establishes the identity of a connecting device through TLS peer-to-peer authentication. (Note that iOS takes care of this stage of connection trust; you do not need to implement anything yourself.) In the course of this procedure, a device initiates a TLS connection with APNs, which returns its server certificate. The device validates this certificate and then sends its device certificate to APNs, which validates that certificate. TLS initiation Device certificate Server certificate TLS established Validate device certificate Device APNS Validate server certificate Provider-to-Service Connection Trust Connection trust between a provider and APNs is also established through TLS peer-to-peer authentication. The procedure is similar to that described in “Service-to-Device Connection Trust” (page 31). The provider initiates a TLS connection, getsthe server certificate from APNs, and validatesthat certificate. Then the provider Apple Push Notification Service Security Architecture 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 31sends its provider certificate to APNs, which validates it on its end. Once this procedure is complete, a secure TLS connection has been established; APNsis now satisfied that the connection has been made by a legitimate provider. TLS initiation Provider certificate Server certificate TLS established Validate provider certificate Provider APNS Validate server certificate Note that provider connection is valid for delivery to only one specific application, identified by the topic (bundle ID) specified in the certificate. APNs also maintains a certificate revocation list; if a provider’s certificate is on this list, APNs may revoke provider trust (that is, refuse the connection). Token Generation and Dispersal An iOS-based application must register to receive push notifications; it typically does this right after it is installed on a device. (This procedure is described in “Scheduling, Registering, and Handling Notifications” (page 15).) iOS receives the registration request from an application, connects with APNs, and forwards the request. Apple Push Notification Service Security Architecture 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 32APNs generates a device token using information contained in the unique device certificate. The device token contains an identifier of the device. It then encrypts the device token with a token key and returns it to the device. Token Connect (Token, ...) Token Generate token package Encrypt token with token key Generate device ID from device certificate Provider Device APNS The device returns the device token to the requesting application as an NSData object. The application then must then deliver the device token to its provider in either binary or hexadecimal format. Figure 3-3 also illustratesthe token generation and dispersalsequence, but in addition showsthe role of the client application in furnishing its provider with the device token. Figure 3-3 Sharing the device token deviceToken APNS Provider Client App 2 1 3 4 SSL connect deviceToken deviceToken The form of this phase of token trust ensures that only APNs generates the token which it will later honor, and it can assure itself that a token handed to it by a device is the same token that it previously provisioned for that particular device—and only for that device. Apple Push Notification Service Security Architecture 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 33Token Trust (Notification) After iOS obtains a device token from APNs, as described in “Token Generation and Dispersal” (page 32), it must provide APNs with the token every time it connects with it. APNs decrypts the device token and validates that the token was generated for the connecting device. To validate, APNs ensures that the device identifier contained in the token matches the device identifier in the device certificate. Every notification that a provider sends to APNs for delivery to a device must be accompanied by the device token it obtained from an application on that device. APNs decrypts the token using the token key, thereby ensuring that the notification is valid. It then uses the device ID contained in the device token to determine the destination device for the notification. Token, Payload Response (OK) Payload Connect (Token, ...) Decrypt token and validate with device certificate Provider APNS Device Decrypt token with token key Trust Components To support the security model for APNs, providers and devices must possess certain certificates, certificate authority (CA) certificates, or tokens. ● Provider: Each provider requires a unique provider certificate and private cryptographic key for validating their connection with APNs. This certificate, provisioned by Apple, must identify the particular topic published by the provider; the topic is the bundle ID of the client application. For each notification, the provider must furnish APNs with a device token identifying the target device. The provider may optionally wish to validate the service it is connecting to using the public server certificate provided by the APNs server. Apple Push Notification Service Security Architecture 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 34● Device: iOS uses the public server certificate passed to it by APNs to authenticate the service that it has connected to. It has a unique private key and certificate that it uses to authenticate itself to the service and establish the TLS connection. It obtains the device certificate and key during device activation and stores them in the keychain. iOS also holds its particular device token, which it receives during the service connection process. Each registered client application isresponsible for delivering thistoken to its content provider. APNs servers also have the necessary certificates, CA certificates, and cryptographic keys (private and public) for validating connections and the identities of providers and devices. The Notification Payload Each push notification carries with it a payload. The payload specifies how users are to be alerted to the data waiting to be downloaded to the client application. The maximum size allowed for a notification payload is 256 bytes; Apple Push Notification Service refuses any notification that exceeds this limit. Remember that delivery of notifications is “best effort” and is not guaranteed. For each notification, providers must compose a JSON dictionary object that strictly adheres to RFC 4627. This dictionary must contain another dictionary identified by the key aps. The aps dictionary contains one or more properties that specify the following actions: ● An alert message to display to the user ● A number to badge the application icon with ● A sound to play Note: Although you can combine an alert message, icon badging, and a sound in a single notification, you should consider the human-interface implications with push notifications. For example, a user might find frequent alert messages with accompanying sound more annoying than useful, especially when the data to be downloaded is not critical. If the target application isn’t running when the notification arrives, the alert message, sound, or badge value is played orshown. If the application isrunning, iOS deliversit to the application delegate as an NSDictionary object. The dictionary contains the corresponding Cocoa property-list objects (plus NSNull). Providers can specify custom payload values outside the Apple-reserved aps namespace. Custom values must use the JSON structured and primitive types: dictionary (object), array,string, number, and Boolean. You should not include customer information as custom payload data. Instead, use it for such purposes as setting context (for the user interface) or internal metrics. For example, a custom payload value might be a conversation Apple Push Notification Service The Notification Payload 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 35identifier for use by an instant-message client application or a timestamp identifying when the provider sent the notification. Any action associated with an alert message should not be destructive—for example, deleting data on the device. Important: Because delivery is not guaranteed, you should not depend on the remote-notificationsfacility for delivering critical data to an application via the payload. And never include sensitive data in the payload. You should use it only to notify the user that new data is available. Table 3-1 lists the keys and expected values of the aps payload. Table 3-1 Keys and values of the aps dictionary Key Value type Comment If this property is included, iOS displays a standard alert. You may specify a string asthe value of alert or a dictionary asits value. If you specify a string, it becomes the message text of an alert with two buttons: Close and View. If the user taps View, the application is launched. Alternatively, you can specify a dictionary as the value of alert. See Table 3-2 (page 36) for descriptions of the keys of this dictionary. string or dictionary alert The number to display as the badge of the application icon. If this property is absent, the badge is not changed. To remove the badge, set the value of this property to 0. badge number The name of a sound file in the application bundle. The sound in this file is played as an alert. If the sound file doesn’t exist or default is specified as the value, the default alert sound is played. The audio must be in one of the audio data formats that are compatible with system sounds; see “Preparing Custom Alert Sounds” (page 15) for details. sound string Table 3-2 Child properties of the alert property Value Comment type Key body string The text of the alert message. Apple Push Notification Service The Notification Payload 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 36Value Comment type Key If a string is specified, displays an alert with two buttons, whose behavior is described in Table 3-1. However, iOS uses the string as a key to get a localized string in the current localization to use for the right button’s title instead of “View”. If the value is null, the system displays an alert with a single OK button that simply dismisses the alert when tapped. See “Localized Formatted Strings” (page 37) for more information. string or null action-loc-key A key to an alert-message string in a Localizable.strings file for the current localization (which is set by the user’s language preference). The key string can be formatted with %@ and %n$@ specifiers to take the variables specified in loc-args. See “Localized Formatted Strings” (page 37) for more information. loc-key string Variable string values to appear in place of the format specifiers in loc-key. See “Localized Formatted Strings” (page 37) for more information. array of strings loc-args The filename of an image file in the application bundle; it may include the extension or omit it. The image is used as the launch image when userstap the action button or move the action slider. If this property is notspecified, the system either usesthe previous snapshot,uses the image identified by the UILaunchImageFile key in the application’s Info.plist file, or falls back to Default.png. This property was added in iOS 4.0. launch-image string Note: If you want the iPhone, iPad, or iPod touch device to display the message text as-is in an alert that has both the Close and View buttons, then specify a string as the direct value of alert. Don’t specify a dictionary as the value of alert if the dictionary only has the body property. Localized Formatted Strings You can display localized alert messages in two ways. The server originating the notification can localize the text; to do this, it must discover the current language preference selected for the device (see “Passing the Provider the Current Language Preference (Remote Notifications)” (page 26)). Or the client application can store in its bundle the alert-message strings translated for each localization it supports. The provider specifies the loc-key and loc-args properties in the aps dictionary of the notification payload. When the device receives the notification (assuming the application isn’t running), it uses these aps-dictionary properties to find and format the string localized for the current language, which it then displays to the user. Apple Push Notification Service The Notification Payload 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 37Here’s how that second option works in a little more detail. An iOS application can internationalize resources such as images, sounds, and text for each language that it supports, Internationalization collects the resources and puts them in a subdirectory of the bundle with a two-part name: a language code and an extension of .lproj (for example, fr.lproj). Localized strings that are programmatically displayed are put in a file called Localizable.strings. Each entry in this file has a key and a localized string value; the string can have format specifiers for the substitution of variable values. When an application asksfor a particular resource—say a localized string—it getsthe resource that islocalized for the language currently selected by the user. For example, if the preferred language is French, the corresponding string value for an alert message would be fetched from Localizable.strings in the fr.lproj directory in the application bundle. (iOS makes this request through the NSLocalizedString macro.) Note: This general pattern is also followed when the value of the action-loc-key property is a string. This string is a key into the Localizable.strings in the localization directory for the currently selected language. iOS uses this key to get the title of the button on the right side of an alert message (the “action” button). To make this clearer, let’s consider an example. The provider specifies the following dictionary as the value of the alert property: "alert" : { "loc-key" : "GAME_PLAY_REQUEST_FORMAT", "loc-args" : [ "Jenna", "Frank"] }, When the device receives the notification, it uses "GAME_PLAY_REQUEST_FORMAT" as a key to look up the associated string value in the Localizable.strings file in the .lproj directory for the current language. Assuming the current localization has an Localizable.strings entry such as this: "GAME_PLAY_REQUEST_FORMAT" = "%@ and %@ have invited you to play Monopoly"; the device displays an alert with the message “Jenna and Frank have invited you to play Monopoly”. In addition to the format specifier %@, you can %n$@ format specifiers for positional substitution of string variables. The n is the index (starting with 1) of the array value in loc-args to substitute. (There’s also the %% specifier for expressing a percentage sign (%).) So if the entry in Localizable.strings is this: "GAME_PLAY_REQUEST_FORMAT" = "%2$@ and %1$@ have invited you to play Monopoly"; Apple Push Notification Service The Notification Payload 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 38the device displays an alert with the message "Frank and Jenna have invited you to play Monopoly". For a full example of a notification payload that usesthe loc-key and loc-arg properties,see the last example of “Examples of JSON Payloads.” To learn more about internationalization in iOS, see ““Advanced App Tricks”” in iOS App Programming Guide ; for general information about internationalization, see Internationalization Programming Topics. String formatting is discussed in “Formatting String Objects” in String Programming Guide . Note: You should use the loc-key and loc-args properties—and the alert dictionary in general—only if you absolutely need to. The values of these properties, especially if they are long strings, might use up more bandwidth than is good for performance. Many if not most applications may not need these properties because their message strings are originated by users and thus are implicitly "localized." Examples of JSON Payloads The following examples of the payload portion of notifications illustrate the practical use of the properties listed in Table 3-1. Properties with “acme” in the key name are examples of custom payload data. The examples include whitespace and newline characters for readability; for better performance, providers should omit whitespace and newline characters. Example 1: The following payload has an aps dictionary with a simple, recommended form for alert messages with the default alert buttons (Close and View). It uses a string as the value of alert rather than a dictionary. This payload also has a custom array property. { "aps" : { "alert" : "Message received from Bob" }, "acme2" : [ "bang", "whiz" ] } Example 2. The payload in the example uses an aps dictionary to request that the device display an alert message with an Close button on the left and a localized title for the "action" button on the right side of the alert. In this case, “PLAY” is used as a key into the Localizable.strings file for the currently selected language to get the localized equivalent of “Play”. The aps dictionary also requests that the application icon be badged with 5. { "aps" : { "alert" : { "body" : "Bob wants to play poker", "action-loc-key" : "PLAY" }, "badge" : 5, }, "acme1" : "bar", "acme2" : [ "bang", "whiz" ] } Apple Push Notification Service The Notification Payload 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 39Example 3. The payload in this example specifies that device should display an alert message with both Close and View buttons. It also request that the application icon be badged with 9 and that a bundled alert sound be played when the notification is delivered. { "aps" : { "alert" : "You got your emails.", "badge" : 9, "sound" : "bingbong.aiff" }, "acme1" : "bar", "acme2" : 42 } Example 4. The interesting thing about the payload in this example is that it uses the loc-key and loc-args child properties of the alert dictionary to fetch a formatted localized string from the application’s bundle and substitute the variable string values(loc-args) in the appropriate places. It also specifies a custom sound and include a custom property. { "aps" : { "alert" : { "loc-key" : "GAME_PLAY_REQUEST_FORMAT", "loc-args" : [ "Jenna", "Frank"] }, "sound" : "chime" }, "acme" : "foo" } Example 5. The following example shows an empty aps dictionary; because the badge property is missing, any current badge number shown on the application icon is removed. The acme2 custom property is an array of two integers. { "aps" : { }, "acme2" : [ 5, 8 ] Apple Push Notification Service The Notification Payload 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 40} Remember, for better performance, you should strip all whitespace and newline characters from the payload before including it in the notification. Apple Push Notification Service The Notification Payload 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 41Sandbox and Production Environments To develop and deploy the provider side of a client/server application, you must get SSL certificates from the appropriate Dev Center. Each certificate is limited to a single application, identified by its bundle ID. Each certificate is also limited to one of two development environments, each with its own assigned IP address: ● Sandbox: The sandbox environment is used for initial development and testing of the provider application. It provides the same set of services as the production environment, although with a smaller number of server units. The sandbox environment also acts a virtual device, enabling simulated end-to-end testing. You accessthe sandbox environment at gateway.sandbox.push.apple.com, outbound TCP port 2195. ● Production: Use the production environment when building the production version of the provider application. Applications using the production environment must meet Apple’s reliability requirements. You access the production environment at gateway.push.apple.com, outbound TCP port 2195. You must getseparate certificatesfor the sandbox (development) environment and the production environment. The certificates are associated with an identifier of the application that is the recipient of push notifications; this identifier includes the application’s bundle ID. When you create a provisioning profile for one of the environments, the requisite entitlements are automatically added to the profile, including the entitlement specific to push notifications, . The two provisioning profiles are called Development and Distribution. The Distribution provisioning profile is a requirement for submitting your application to the App Store. OS X Note: The entitlement for the OS X provisioning profile is com.apple.developer.aps-environment, which scopes it to the platform. You can determine in Xcode which environment you are in by the selection of a code-signing identity. If you see an “iPhone Developer: Firstname Lastname ” certificate/provisioning profile pair, you are in the sandbox environment. If you see an “iPhone Distribution: Companyname ” certificate/provisioning profile pair, you are in the production environment. It is a good idea to create a Distribution release configuration in Xcode to help you further differentiate the environments. 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 42 Provisioning and DevelopmentAlthough an SSL certificate is not put into a provisioning profile, the is added to the profile because of the association of the certificate and a particular application ID. As a result this entitlement is built into the application, which enables it to receive push notifications. Provisioning Procedures In the iOS Developer Program, each member on a development team has one of three roles: team agent, team admin, and team member. The roles differ in relation to iPhone development certificates and provisioning profiles. The team agent isthe only person on the team who can create Development (Sandbox) SSL certificates and Distribution (Production) SSL certificates. The team admin and the team agent can both create both Development and Distribution provisioning profiles. Team members may only download and install certificates and provisioning profiles. The procedures in the following sections make reference to these roles. Note: The iOS Provisioning Portal makes available to all iOS Developer Program members a user guide and a series of videos that explain all aspects of certificate creation and provisioning. The following sections focus on APNs-specific aspects of the process and summarize other aspects. To access the portal, iOS Developer Program members should go to the iOS Dev Center (http://developer.apple.com/devcenter/ios), log in, and click then go to the iOS Provisioning Portal page (there’s a link in the upper right). Creating the SSL Certificate and Keys In the provisioning portal of the iOS Dev Center, the team agent selects the application IDs for APNs. He also completes the following steps to create the SSL certificate: 1. Click App IDs in the sidebar on the left side of the window. The next page displays your valid application IDs. An application ID consists of an application’s bundle ID prefixed with a ten-character code generated by Apple. The team admin must enter the bundle ID. For a certificate, it must incorporate a specific bundle ID; you cannot use a “wildcard” application ID. 2. Locate the application ID for the sandbox SSL certificate (and that is associated with the Development provisioning profile) and click Configure. You must see “Available” under the Apple Push Notification Service column to configure a certificate for this application ID. 3. In the Configure App ID page, check the Enable Push Notification Services box and click the Configure button. Clicking this button launches an APNs Assistant, which guides you through the next series of steps. Provisioning and Development Provisioning Procedures 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 434. The first step requires that you launch the Keychain Access application and generate a Certificate Signing Request (CSR). Follow the instructions presented in the assistant. When you are finished generating a CSR, click Continue in Keychain Access to return to the APNs Assistant. When you create a CSR, Keychain Access generates a private and a public cryptographic key pair. The private key is put into your Login keychain by default. The public key is included in the CSR sent to the provisioning authority. When the provisioning authority sendsthe certificate back to you, one of the items in that certificate is the public key. 5. In the Submit Certificate Signing Request pane, click Choose File. Navigate to the CSR file you created in the previous step and select it. 6. Click the Generate button. While displaying the Generate Your Certificate pane, the Assistant configures and generates your Client SSL Certificate. If it succeeds, it displays the message “Your APNs Certificate has been generated.” Click Continue to proceed to the next step. 7. In the next pane, click the Download Now button to download the certificate file to your download location. Navigate to that location and double-click the certificate file (which has an extension of cer) to install it in your keychain. When you are finished, click Done in the APNs Assistant. Double-clicking the file launches Keychain Access. Make sure you install the certificate in your login keychain on the computer you are using for provider development. In Keychain Access, ensure that your certificate user ID matches your application’s bundle ID. The APNs SSL certificate should be installed on your notification server. When you finish these steps you are returned to the Configure App ID page of the iOS Dev Center portal. The certificate should be badged with a green circle and the label “Enabled”. To create a certificate for the production environment, repeat the same procedure but choose the application ID for the production certificate. Creating and Installing the Provisioning Profile The Team Admin or Team Agent must next create the provisioning profile (Development or Distribution) used in the server side of remote-notification development. The provisioning profile is a collection of assets that associates developers of an application and their devices with an authorized development team and enables those devicesto be used for testing. The profile contains certificates, device identifiers, the application’s bundle ID, and all entitlements, including . All team members must install the provisioning profile on the devices on which they will run and test application code. Provisioning and Development Provisioning Procedures 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 44Note: Refer to the program user guide for the details of creating a provisioning profile. To download and install the provisioning profile, team members should complete the following steps: 1. Go to the provisioning portal in the iOS Dev Center. 2. Create a new provisioning profile that contains the App ID you registered for APNs. 3. Modify any existing profile before you download the new one. You have to modify the profile in some minor way (for example, toggle an option) for the portal to generate a new provisioning profile. If the profile isn't so “dirtied,” you're given the original profile without the push entitlements. 4. From the download location, drag the profile file (which has an extension of mobileprovision) onto the Xcode or iTunes application icons. Alternatively, you can move the profile file to ~/Library/MobileDevice/Provisioning Profiles. Create the directory if it does not exist. 5. Verify that the entitlements in the provisioning-profile file are correct. To do this, open the .mobileprovision file in a text editor. The contents of the file are structured in XML. In the Entitlements dictionary locate the aps-environment key. For a development provisioning profile, the string value of this key should be development; for a distribution provisioning profile, the string value should be production. 6. In the Xcode Organizer window, go the Provisioning Profiles section and install the profile on your device. When you build the project, the binary is now signed by the certificate using the private key. Installing the SSL Certificate and Key on the Server You should install the SSL distribution certificate and private cryptographic key you obtained earlier on the server computer on which the provider code runs and from which it connects with the sandbox or production versions of APNs. To do so, complete the following steps: 1. Open Keychain Access utility and click the My Certificates category in the left pane. 2. Find the certificate you want to install and disclose its contents. You'll see both a certificate and a private key. 3. Select both the certificate and key, choose File > Export Items, and export them as a Personal Information Exchange (.p12) file. 4. Servers implemented in languages such as Ruby and Perl often are better able to deal with certificates in the Personal Information Exchange format. To convert the certificate to thisformat, complete the following steps: Provisioning and Development Provisioning Procedures 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 45a. In KeyChain Access,select the certificate and choose File > Export Items. Select the Personal Information Exchange (.p12) option, select a save location, and click Save. b. Launch the Terminal application and enter the following command after the prompt: openssl pkcs12 -in CertificateName.p12 -out CertificateName.pem -nodes 5. Copy the .pem certificate to the new computer and install it in the appropriate place. Provisioning and Development Provisioning Procedures 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 46This chapter describesthe interfacesthat providers use for communication with Apple Push Notification service (APNs) and discusses some of the functions that providers are expected to fulfill. General Provider Requirements As a provider you communicate with Apple Push Notification service over a binary interface. This interface is a high-speed, high-capacity interface for providers; it uses a streaming TCP socket design in conjunction with binary content. The binary interface is asynchronous. The binary interface of the production environment is available through gateway.push.apple.com, port 2195; the binary interface of the sandbox (development) environment is available through gateway.sandbox.push.apple.com, port 2195. You may establish multiple, parallel connections to the same gateway or to multiple gateway instances. For each interface you should use TLS (or SSL) to establish a secured communications channel. The SSL certificate required for these connections is provisioned through the iOS Provisioning Portal. (See “Provisioning and Development” (page 42) for details.) To establish a trusted provider identity, you should present this certificate to APNs at connection time using peer-to-peer authentication. Note: To establish a TLS session with APNs, an Entrust Secure CA root certificate must be installed on the provider’s server. If the server is running OS X, this root certificate is already in the keychain. On other systems, the certificate might not be available. You can download this certificate from the Entrust SSL Certificates website. You should also retain connections with APNs across multiple notifications. APNs may consider connections that are rapidly and repeatedly established and torn down as a denial-of-service attack. Upon error, APNs closes the connection on which the error occurred. As a provider, you are responsible for the following aspects of push notifications: ● You must compose the notification payload (see “The Notification Payload” (page 35)). ● You are responsible for supplying the badge number to be displayed on the application icon. 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 47 Provider Communication with Apple Push Notification Service● You should regularly connect with the feedback web server and fetch the current list of those devices that have repeatedly reported failed-delivery attempts. Then you should cease sending notifications to the devices associated with those applications. See “The Feedback Service” (page 53) for more information. If you intend to support notification messagesin multiple languages, but do not use the loc-key and loc-args properties of the aps payload dictionary for client-side fetching of localized alert strings, you need to localize the text of alert messages on the server side. To do this, you need to find out the current language preference from the client application. “Scheduling, Registering, and Handling Notifications” (page 15) suggests an approach for obtaining this information. See “The Notification Payload” (page 35) for information about the loc-key and loc-args properties. The Binary Interface and Notification Formats The binary interface employs a plain TCP socket for binary content that is streaming in nature. For optimum performance, you should batch multiple notificationsin a single transmission over the interface, either explicitly or using a TCP/IP Nagle algorithm. The interface supports two formats for notification packets, a simple format and an enhanced format that addresses some of the issues with the simple format: ● Notification expiry. APNs has a store-and-forward feature that keeps the most recent notification sent to an application on a device. If the device is offline at time of delivery, APNs delivers the notification when the device next comes online. With the simple format, the notification is delivered regardless of the pertinence of the notification. In other words, the notification can become “stale” over time. The enhanced format includes an expiry value that indicates the period of validity for a notification. APNs discards a notification in store-and-forward when this period expires. ● Error response. With the simple format, if you send a notification packet that is malformed in some way—for example, the payload exceeds the stipulated limit—APNs responds by severing the connection. It gives no indication why it rejected the notification. The enhanced format lets a provider tag a notification with an arbitrary identifier. If there is an error, APNs returns a packet that associates an error code with the identifier. This response enables the provider to locate and correct the malformed notification. The enhanced format is recommended for most providers. Provider Communication with Apple Push Notification Service The Binary Interface and Notification Formats 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 48Let’s examine the simple notification format first because much of this format is shared with the enhanced format. Figure 5-1 illustrates this format. Figure 5-1 Simple notification format 0 0 32 deviceToken (binary) 0 34 {"aps":{"alert":"You have mail!"}} Bytes: 1 2 32 2 Command Token length Payload length (big endian) (big endian) 34 The first byte in the simple format is a command value of 0 (zero). The lengths of the device token and the payload must be in network order (that is, big endian). In addition, you should encode the device token in binary format. The payload must not exceed 256 bytes and must not be null-terminated. Listing 5-1 gives an example of a function that sends a push notification to APNs over the binary interface using the simple notification format. The example assumes prior SSL connection to gateway.push.apple.com (or gateway.sandbox.push.apple.com) and peer-exchange authentication. Listing 5-1 Sending a notification in the simple format via the binary interface static bool sendPayload(SSL *sslPtr, char *deviceTokenBinary, char *payloadBuff, size_t payloadLength) { bool rtn = false; if (sslPtr && deviceTokenBinary && payloadBuff && payloadLength) { uint8_t command = 0; /* command number */ char binaryMessageBuff[sizeof(uint8_t) + sizeof(uint16_t) + DEVICE_BINARY_SIZE + sizeof(uint16_t) + MAXPAYLOAD_SIZE]; /* message format is, |COMMAND|TOKENLEN|TOKEN|PAYLOADLEN|PAYLOAD| */ char *binaryMessagePt = binaryMessageBuff; uint16_t networkOrderTokenLength = htons(DEVICE_BINARY_SIZE); uint16_t networkOrderPayloadLength = htons(payloadLength); /* command */ *binaryMessagePt++ = command; /* token length network order */ Provider Communication with Apple Push Notification Service The Binary Interface and Notification Formats 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 49memcpy(binaryMessagePt, &networkOrderTokenLength, sizeof(uint16_t)); binaryMessagePt += sizeof(uint16_t); /* device token */ memcpy(binaryMessagePt, deviceTokenBinary, DEVICE_BINARY_SIZE); binaryMessagePt += DEVICE_BINARY_SIZE; /* payload length network order */ memcpy(binaryMessagePt, &networkOrderPayloadLength, sizeof(uint16_t)); binaryMessagePt += sizeof(uint16_t); /* payload */ memcpy(binaryMessagePt, payloadBuff, payloadLength); binaryMessagePt += payloadLength; if (SSL_write(sslPtr, binaryMessageBuff, (binaryMessagePt - binaryMessageBuff)) > 0) rtn = true; } return rtn; } Figure 5-2 depicts the enhanced format for notification packets. With this format, if APNs encounters an unintelligible command, it returns an error response before disconnecting. Figure 5-2 Enhanced notification format 1 Identifier Bytes: 1 4 Expiry 4 Command 32 deviceToken (binary) 0 34 {"aps":{"alert":"You have mail!"}} 2 32 2 Token length Payload length (big endian) (big endian) 34 0 The first byte in the enhanced notification format is a command value of 1. The two new fields in this format are for an identifier and an expiry value. (Everything else is the same as the simple notification format.) ● Identifier—An arbitrary value that identifies this notification. This same identifier is returned in a error-response packet if APNs cannot interpret a notification. Provider Communication with Apple Push Notification Service The Binary Interface and Notification Formats 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 50● Expiry—A fixed UNIX epoch date expressed in seconds (UTC) that identifies when the notification is no longer valid and can be discarded. The expiry value should be in network order (big endian). If the expiry value is positive, APNs tries to deliver the notification at least once. You can specify zero or a value less than zero to request that APNs not store the notification at all. If you send a notification and APNs finds the notification malformed or otherwise unintelligible, it returns an error-response packet prior to disconnecting. (If there is no error, APNs doesn’t return anything.) Figure 5-3 depicts the format of the error-response packet. Figure 5-3 Format of error-response packet 8 Bytes: 1 Command Status n Identifier 1 4 The packet has a command value of 8 followed by a one-byte status code and the same notification identifier specified by the provider when it composed the notification. Table 5-1 lists the possible status codes and their meanings. Table 5-1 Codes in error-response packet Status code Description 0 No errors encountered 1 Processing error 2 Missing device token 3 Missing topic 4 Missing payload 5 Invalid token size 6 Invalid topic size 7 Invalid payload size 8 Invalid token 255 None (unknown) Provider Communication with Apple Push Notification Service The Binary Interface and Notification Formats 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 51Listing 5-2 modifies the code in Listing 5-1 (page 49) to compose a push notification in the enhanced format before sending it to APNs. As with the earlier example, it assumes prior SSL connection to gateway.push.apple.com (or gateway.sandbox.push.apple.com) and peer-exchange authentication. Listing 5-2 Sending a notification in the enhanced format via the binary interface static bool sendPayload(SSL *sslPtr, char *deviceTokenBinary, char *payloadBuff, size_t payloadLength) { bool rtn = false; if (sslPtr && deviceTokenBinary && payloadBuff && payloadLength) { uint8_t command = 1; /* command number */ char binaryMessageBuff[sizeof(uint8_t) + sizeof(uint32_t) + sizeof(uint32_t) + sizeof(uint16_t) + DEVICE_BINARY_SIZE + sizeof(uint16_t) + MAXPAYLOAD_SIZE]; /* message format is, |COMMAND|ID|EXPIRY|TOKENLEN|TOKEN|PAYLOADLEN|PAYLOAD| */ char *binaryMessagePt = binaryMessageBuff; uint32_t whicheverOrderIWantToGetBackInAErrorResponse_ID = 1234; uint32_t networkOrderExpiryEpochUTC = htonl(time(NULL)+86400); // expire message if not delivered in 1 day uint16_t networkOrderTokenLength = htons(DEVICE_BINARY_SIZE); uint16_t networkOrderPayloadLength = htons(payloadLength); /* command */ *binaryMessagePt++ = command; /* provider preference ordered ID */ memcpy(binaryMessagePt, &whicheverOrderIWantToGetBackInAErrorResponse_ID, sizeof(uint32_t)); binaryMessagePt += sizeof(uint32_t); /* expiry date network order */ memcpy(binaryMessagePt, &networkOrderExpiryEpochUTC, sizeof(uint32_t)); binaryMessagePt += sizeof(uint32_t); Provider Communication with Apple Push Notification Service The Binary Interface and Notification Formats 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 52/* token length network order */ memcpy(binaryMessagePt, &networkOrderTokenLength, sizeof(uint16_t)); binaryMessagePt += sizeof(uint16_t); /* device token */ memcpy(binaryMessagePt, deviceTokenBinary, DEVICE_BINARY_SIZE); binaryMessagePt += DEVICE_BINARY_SIZE; /* payload length network order */ memcpy(binaryMessagePt, &networkOrderPayloadLength, sizeof(uint16_t)); binaryMessagePt += sizeof(uint16_t); /* payload */ memcpy(binaryMessagePt, payloadBuff, payloadLength); binaryMessagePt += payloadLength; if (SSL_write(sslPtr, binaryMessageBuff, (binaryMessagePt - binaryMessageBuff)) > 0) rtn = true; } return rtn; } Take note that the device token in the production environment and the device token in the development (sandbox) environment are not the same value. The Feedback Service If a provider attempts to deliver a push notification to an application, but the application no longer exists on the device, the device reports that fact to Apple Push Notification Service. This situation often happens when the user has uninstalled the application. If a device reports failed-delivery attempts for an application, APNs needs some way to inform the provider so that it can refrain from sending notifications to that device. Doing this reduces unnecessary message overhead and improves overall system performance. For this purpose Apple Push Notification Service includes a feedback service that APNs continually updates with a per-application list of devices for which there were failed-delivery attempts. The devices are identified by device tokens encoded in binary format. Providers should periodically query the feedback service to get Provider Communication with Apple Push Notification Service The Feedback Service 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 53the list of device tokens for their applications, each of which is identified by its topic. Then, after verifying that the application hasn’t recently been re-registered on the identified devices, a provider should stop sending notifications to these devices. Access to the feedback service takes place through a binary interface similar to that used for sending push notifications. You access the production feedback service via feedback.push.apple.com, port 2196; you access the sandbox feedback service via feedback.sandbox.push.apple.com, port 2196. As with the binary interface for push notifications, you must use TLS (or SSL) to establish a secured communications channel. The SSL certificate required for these connections is the same one that is provisioned for sending notifications. To establish a trusted provider identity, you should present this certificate to APNs at connection time using peer-to-peer authentication. Once you are connected, transmission begins immediately; you do not need to send any command to APNs. Begin reading the stream written by the feedback service until there is no more data to read. The received data is in tuples having the following format: Figure 5-4 Binary format of a feedback tuple n n n n 0 32 deviceToken (binary) Bytes: 4 2 32 Token length time_t (big endian) (big endian) A timestamp (as a four-byte time_t value) indicating when the APNs determined that the application no longer exists on the device. This value, which is in network order, represents the seconds since 1970, anchored to UTC. You should use the timestamp to determine if the application on the device re-registered with your service since the moment the device token was recorded on the feedback service. If it hasn’t, you should cease sending push notifications to the device. Timestamp Token length The length of the device token as a two-byte integer value in network order. Device token The device token in binary format. Note: APNs monitors providers for their diligence in checking the feedback service and refraining from sending push notifications to nonexistent applications on devices. Provider Communication with Apple Push Notification Service The Feedback Service 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 54This table describes the changes to Local and Push Notification Programming Guide . Date Notes Added information about implementing push notifications on an OS X desktop client. Unified the guide for iOS and OS X. 2011-08-09 Describes how to determine if an application is launched because the user tapped the notification alert's action button. 2010-08-03 2010-07-08 Changed occurrences of "iPhone OS" to "iOS." Updated and reorganized to describe local notifications, a feature introduced in iOS 4.0. Also describes a new format for push notifications sent to APNs. 2010-05-27 2010-01-28 Made many small corrections. Made minor corrections and linked to short inline articles on Cocoa concepts. 2009-08-14 Added notes about Wi-Fi and frequency of registration, and gateway address for sandbox. Updated with various clarifications and enhancements. 2009-05-22 First version of a document that explains how providers can send push notifications to client applications using Apple Push Notification Service. 2009-03-15 2011-08-09 | © 2011 Apple Inc. All Rights Reserved. 55 Document Revision HistoryApple Inc. © 2011 Apple Inc. All rights reserved. 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Mac App Programming GuideContents About OS X App Design 7 At a Glance 7 Cocoa Helps You Create Great Apps for OS X 7 Common Behaviors Make Apps Complete 8 Get It Right: Meet System and App Store Requirements 8 Finish Your App with Performance Tuning 8 How to Use This Document 9 See Also 9 The Mac Application Environment 10 An Environment Designed for Ease of Use 10 A Sophisticated Graphics Environment 11 Low-Level Details of the Runtime Environment 12 Based on UNIX 12 Concurrency and Threading 12 The File System 13 Security 18 The Core App Design 21 Fundamental Design Patterns 21 The App Style Determines the Core Architecture 23 The Core Objects for All Cocoa Apps 26 Additional Core Objects for Multiwindow Apps 29 Integrating iCloud Support Into Your App 30 Shoebox-Style Apps Should Not Use NSDocument 31 Document-Based Apps Are Based on an NSDocument Subclass 31 Documents in OS X 31 The Document Architecture Provides Many Capabilities for Free 32 The App Life Cycle 33 The main Function is the App Entry Point 33 The App’s Main Event Loop Drives Interactions 34 Automatic and Sudden Termination of Apps Improve the User Experience 36 Support the Key Runtime Behaviors in Your Apps 36 Automatic Termination 37 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 2Sudden Termination 38 User Interface Preservation 39 Apps Are Built Using Many Different Pieces 43 The User Interface 44 Event Handling 45 Graphics, Drawing, and Printing 46 Text Handling 47 Implementing the Application Menu Bar 47 Xcode Templates Provide the Menu Bar 48 Connect Menu Items to Your Code or Your First Responder 48 Implementing the Full-Screen Experience 49 Full-Screen API in NSApplication 49 Full-Screen API in NSWindow 50 Full-Screen API in NSWindowDelegate Protocol 50 Supporting Common App Behaviors 53 You Can Prevent the Automatic Relaunch of Your App 53 Making Your App Accessible Enables Many Users 53 Provide User Preferences for Customization 56 Integrate Your App With Spotlight Search 57 Use Services to Increase Your App’s Usefulness 58 Optimize for High Resolution 58 Think About Points, Not Pixels 58 Provide High-Resolution Versions of Graphics 59 Use High-Resolution-Savvy Image-Loading Methods 60 Use APIs That Support High Resolution 60 Prepare for Fast User Switching 61 Take Advantage of the Dock 62 Build-Time Configuration Details 63 Configuring Your Xcode Project 63 The Information Property List File 64 The OS X Application Bundle 66 Internationalizing Your App 69 Tuning for Performance and Responsiveness 71 Speed Up Your App’s Launch Time 71 Delay Initialization Code 71 Simplify Your Main Nib File 72 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 3 ContentsMinimize Global Variables 72 Minimize File Access at Launch Time 73 Don’t Block the Main Thread 73 Decrease Your App’s Code Size 73 Compiler-Level Optimizations 74 Use Core Data for Large Data Sets 75 Eliminate Memory Leaks 75 Dead Strip Your Code 75 Strip Symbol Information 76 Document Revision History 77 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 4 ContentsFigures, Tables, and Listings The Mac Application Environment 10 Table 1-1 Key directories for Mac apps 14 Table 1-2 Attributes for the OS X file system 17 Listing 1-1 Getting the path to the Application Support directory 16 The Core App Design 21 Figure 2-1 The Calculator single-window utility app 24 Figure 2-2 The iPhoto single-window app 25 Figure 2-3 TextEdit document window 26 Figure 2-4 Key objects in a single-window app 27 Figure 2-5 Key objects in a multiwindow document app 29 Figure 2-6 Document file, object, and data model 32 Figure 2-7 The main event loop 35 Figure 2-8 Responder objects targeted by Cocoa for preservation 40 Figure 2-9 Windows and menus in an app 44 Figure 2-10 Processing events in the main run loop 45 Table 2-1 Fundamental design patterns used by Mac apps 21 Table 2-2 The core objects used by all Cocoa apps 27 Table 2-3 Additional objects used by multiwindow document apps 30 Listing 2-1 The main function of a Mac app 34 Listing 2-2 Returning the main window for a single-window app 43 Implementing the Full-Screen Experience 49 Table 3-1 Window delegate methods supporting full-screen mode 51 Supporting Common App Behaviors 53 Figure 4-1 Universal Access system preference dialog 55 Figure 4-2 Spotlight extracting metadata 57 Figure 4-3 Content appears the same size at standard resolution and high resolution 59 Build-Time Configuration Details 63 Figure 5-1 The information property list editor 65 Figure 5-2 The Language preference view 70 Table 5-1 A typical application bundle 66 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 5Tuning for Performance and Responsiveness 71 Table 6-1 Compiler optimization options 74 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 6 Figures, Tables, and ListingsThis document is the starting point for learning how to create Mac apps. It contains fundamental information about the OS X environment and how your apps interact with that environment. It also contains important information about the architecture of Mac apps and tips for designing key parts of your app. At a Glance Cocoa is the application environment that unlocks the full power of OS X. Cocoa provides APIs, libraries, and runtimes that help you create fast, exciting apps that automatically inherit the beautiful look and feel of OS X, as well as standard behaviors users expect. Cocoa Helps You Create Great Apps for OS X You write apps for OS X using Cocoa, which provides a significant amount of infrastructure for your program. Fundamental design patterns are used throughout Cocoa to enable your app to interface seamlessly with subsystem frameworks, and core application objects provide key behaviorsto supportsimplicity and extensibility in app architecture. Key parts of the Cocoa environment are designed particularly to support ease of use, one of the most important aspects of successful Mac apps. Many apps should adopt iCloud to provide a more coherent user experience by eliminating the need to synchronize data explicitly between devices. 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 7 About OS X App DesignRelevant Chapters: “The Mac Application Environment” (page 10), “The Core App Design” (page 21), and “Integrating iCloud Support Into Your App” (page 30) Common Behaviors Make Apps Complete During the design phase of creating your app, you need to think about how to implement certain features that users expect in well-formed Mac apps. Integrating these features into your app architecture can have an impact on the user experience: accessibility, preferences, Spotlight, services, resolution independence, fast user switching, and the Dock. Enabling your app to assume full-screen mode, taking over the entire screen, provides users with a more immersive, cinematic experience and enables them to concentrate fully on their content without distractions. Relevant Chapters: “Supporting Common App Behaviors” (page 53) and “Implementing the Full-Screen Experience” (page 49) Get It Right: Meet System and App Store Requirements Configuring your app properly is an important part of the development process. Mac apps use a structured directory called a bundle to manage their code and resource files. And although most of the files are custom and exist to support your app, some are required by the system or the App Store and must be configured properly. The application bundle also contains the resources you need to provide to internationalize your app to support multiple languages. Relevant Chapter: “Build-Time Configuration Details” (page 63) Finish Your App with Performance Tuning As you develop your app and your project code stabilizes, you can begin performance tuning. Of course, you want your app to launch and respond to the user’s commands as quickly as possible. A responsive app fits easily into the user’s workflow and gives an impression of being well crafted. You can improve the performance of your app by speeding up launch time and decreasing your app’s code footprint. About OS X App Design At a Glance 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 8Relevant Chapter: “Tuning for Performance and Responsiveness” (page 71) How to Use This Document This guide introduces you to the most important technologies that go into writing an app. In this guide you will see the whole landscape of what's needed to write one. That is, this guide shows you all the "pieces" you need and how they fit together. There are important aspects of app design that this guide does not cover, such as user interface design. However, this guide includes many links to other documents that provide details about the technologies it introduces, as well as links to tutorials that provide a hands-on approach. In addition, this guide emphasizes certain technologies introduced in OS X v10.7, which provide essential capabilities that set your app apart from older ones and give it remarkable ease of use, bringing some of the best features from iOS to OS X. See Also The following documents provide additional information about designing Mac apps, as well as more details about topics covered in this document: ● To work through a tutorial showing you how to create a Cocoa app, see Start Developing Mac Apps Today . ● For information about user interface design enabling you to create effective apps using OS X, see OS X Human Interface Guidelines. ● To understand how to create an explicit app ID, create provisioning profiles, and enable the correct entitlementsfor your application,so you can sell your application through the Mac App Store or use iCloud storage, see Tools Workflow Guide for Mac . ● For information about the design patterns used in Cocoa, see Cocoa Fundamentals Guide . ● For a general survey of OS X technologies, see Mac Technology Overview. ● To understand how to implement a document-based app, see Document-Based App Programming Guide for Mac . About OS X App Design How to Use This Document 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 9OS X incorporates the latest technologies for creating powerful and fun-to-use apps. But the technologies by themselves are not enough to make every app great. What sets an app apart from its peers is how it helps the user achieve some tangible goal. After all, users are not going to care what technologies an app uses, as long as it helps them do what they need to do. An app that gets in the user’s way is going to be forgotten, but one that makes work (or play) easier and more fun is going to be remembered. You use Cocoa to write apps for OS X. Cocoa gives you access to all of the features of OS X and allows you to integrate your app cleanly with the rest of the system. This chapter covers the key parts of OS X that help you create great apps. In particular, this chapter describessome of the important ease-of-use technologiesintroduced in OS X v10.7. For a more thorough list of technologies available in OS X, see Mac Technology Overview. An Environment Designed for Ease of Use OS X strives to provide an environment that is transparent to users and as easy to use as possible. By making hard tasks simple and getting out of the way, the system makes it easier for the user to be creative and spend less time worrying about the steps needed to make the computer work. Of course, simplifying tasks means your app has to do more of the work, but OS X provides help in that respect too. As you design your app, you should think about the tasks that users normally perform and find ways to make them easier. OS X supports powerful ease-of-use features and design principles. For example: ● Users should not have to save their work manually. The document model in Cocoa provides support for saving the user’sfile-based documents without user interaction;see “The Document Architecture Provides Many Capabilities for Free” (page 32). ● Apps should restore the user’s work environment at login time. Cocoa provides support for archiving the current state of the app’s interface (including the state of unsaved documents) and restoring that state at launch time; see “User Interface Preservation” (page 39). ● Appsshould support automatic termination so that the user never hasto quit them. Automatic termination means that when the user closes an app’s windows, the app appears to quit but actually just moves to the background quietly. The advantage is that subsequent launches are nearly instant as the app simply moves back to the foreground; see “Automatic and Sudden Termination of Apps Improve the User Experience” (page 36) 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 10 The Mac Application Environment● You should consider providing your users with an immersive, full-screen experience by implementing a full-screen version of your user interface. The full-screen experience eliminates outside distractions and allows the user to focus on their content; see “Implementing the Full-Screen Experience” (page 49). ● Support trackpad gestures for appropriate actions in your app. Gestures provide simple shortcuts for common tasks and can be used to supplement existing controls and menu commands. OS X provides automatic support for reporting gestures to your app through the normal event-handling mechanism; see Cocoa Event Handling Guide . ● Consider minimizing or eliminating the user’s interactions with the raw file system. Rather than expose the entire file system to the user through the open and save panels, some apps, in the manner of iPhoto and iTunes, can provide a better user experience by presenting the user’s content in a simplified browser designed specifically for the app’s content. OS X uses a well-defined file system structure that allows you to place and find files easily and includes many technologies for accessing those files; see “The File System” (page 13). ● For apps that support custom document types, provide a Quick Look plug-in so that users can view your documents from outside of your app; see Quick Look Programming Guide . ● Apps should support the fundamental features for the OS X user experience that make apps elegant and intuitive,such as direct manipulation and drag-and-drop. Usersshould remain in control, receive consistent feedback, and be able to explore because the app is forgiving with reversible actions; see OS X Human Interface Guidelines. All of the preceding features are supported by Cocoa and can be incorporated with relatively little effort. A Sophisticated Graphics Environment High-quality graphics and animation make your app look great and can convey a lot of information to the user. Animations in particular are a great way to provide feedback about changes to your user interface. So as you design your app, keep the following ideas in mind: ● Use animations to provide feedback and convey changes. Cocoa provides mechanisms for creating sophisticated animations quickly in both the AppKit and Core Animation frameworks. For information about creating view-based animations, see Cocoa Drawing Guide . For information about using Core Animation to create your animations, see Core Animation Programming Guide . ● Include high-resolution versions of your art and graphics. OS X automatically loads high-resolution image resources when an app runs on a screen whose scaling factor is greater than 1.0. Including such image resources makes your app’s graphics look even sharper and crisper on those higher-resolution screens. Forinformation aboutthe graphicstechnologies available inOS X,see “Media Layer” in Mac TechnologyOverview. The Mac Application Environment A Sophisticated Graphics Environment 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 11Low-Level Details of the Runtime Environment When you are ready to begin writing actual code, there are a lot of technologies available to make your life easier. OS X supports all of the basic features such as memory management, file management, networking, and concurrency that you need to write your code. In some cases, though, OS X also provides more sophisticated services (or specific coding conventions) that, when followed, can make writing your code even easier. Based on UNIX OS X is powered by a 64-bit Mach kernel, which manages processor resources, memory, and other low-level behaviors. On top of the kernel sits a modified version of the Berkeley Software Distribution (BSD) operating system, which provides interfaces that apps can use to interact with the lower-level system. This combination of Mach and BSD provides the following system-level support for your apps: ● Preemptive multitasking—All processes share the CPU efficiently. The kernel schedules processes in a way that ensures they all receive the time they need to run. Even background apps continue to receive CPU time to execute ongoing tasks. ● Protected memory—Each process runs in its own protected memory space, which prevents processes from accidentally interfering with each other. (Apps can share part of their memory space to implement fast interprocess communication but take responsibility for synchronizing and locking that memory appropriately.) ● Virtual memory—64-bit apps have a virtual address space of approximately 18 exabytes (18 billion billion bytes). (If you create a 32-bit app, the amount of virtual memory is only 4 GB.) When an app’s memory usage exceedsthe amount of free physical memory, the system transparently writes pagesto disk to make more room. Written out pages remain on disk until they are needed in memory again or the app exits. ● Networking and Bonjour—OS X provides support for the standard networking protocols and services in use today. BSD sockets provide the low-level communication mechanism for apps, but higher-level interfaces also exist. Bonjour simplifies the user networking experience by providing a dynamic way to advertise and connect to network services over TCP/IP. For detailed information about the underlying environment of OS X, see “Kernel and Device Drivers Layer” in Mac Technology Overview. Concurrency and Threading Each process starts off with a single thread of execution and can create more threads as needed. Although you can create threads directly using POSIX and other higher-level interfaces, for most types of work it is better to create them indirectly using block objects with Grand Central Dispatch (GCD) or operation objects, a Cocoa concurrency technology implemented by the NSOperation class. The Mac Application Environment Low-Level Details of the Runtime Environment 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 12GCD and operation objects are an alternative to raw threads that simplify or eliminate many of the problems normally associated with threaded programming,such assynchronization and locking. Specifically, they define an asynchronous programming model in which you specify only the work to be performed and the order in which you want it performed. The system then handles the tedious work required to schedule the necessary threads and execute your tasks as efficiently as possible on the current hardware. You should not use GCD or operations for work requiring time-sensitive data processing (such as audio or video playback), but you can use them for most other types of tasks. For more information on using GCD and operation objects to implement concurrency in your apps, see Concurrency Programming Guide . The File System The file system in OS X is structured to provide a better experience for users. Rather than exposing the entire file system to the user, the Finder hides any files and directories that an average user should not need to use, such as the contents of low-level UNIX directories. This is done to provide a simpler interface for the end user (and only in places like the Finder and the open and save panels). Apps can still access any files and directories for which they have valid permissions, regardless of whether they are hidden by the Finder. When creating apps, you should understand and follow the conventions associated with the OS X file system. Knowing where to put files and how to get information out of the file system ensures a better user experience. A Few Important App Directories The OS X file system is organized in a way that groups related files and data together in specific places. Every file in the file system has its place and apps need to know where to put the files they create. This is especially important if you are distributing your app through the App Store, which expects you to put your app’s data files in specific directories. Table 1-1 lists the directories with which apps commonly interact. Some of these directories are inside the home directory, which is either the user’s home directory or, if the app adopts App Sandbox, the app’s container directory as described in “App Sandbox and XPC” (page 18). Because the actual paths can differ based on these conditions, use the URLsForDirectory:inDomains: method of the NSFileManager classto retrieve the actual directory path. You can then add any custom directory and filename information to the returned URL object to complete the path. The Mac Application Environment Low-Level Details of the Runtime Environment 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 13Table 1-1 Key directories for Mac apps Directory Description Thisisthe installation directory for your app bundle. The path for the global Applications directory is /Applications but each user directory may have a local applications directory containing user-specific apps. Regardless, you should not need to use this path directly. To access resources inside your application bundle, use an NSBundle object instead. For more information about the structure of your application bundle and how you locate resources, see “The OS X Application Bundle” (page 66). Applications directory The configuration of your app determines the location of the home directory seen by your app: ● For apps running in a sandbox in OS X v10.7 and later, the home directory is the app’s container directory. For more information about the container directory, see “The Keychain” (page 20). ● For apps running outside of a sandbox (including those running in versions of OS X before 10.7), the home directory isthe user-specific subdirectory of /Users that contains the user’s files. To retrieve the path to the home directory, use the NSHomeDirectory function. Home directory The Library directory is the top-level directory for storing private app-related data and preferences. There are several Library directories scattered throughout the system but you should always use the one located inside the current home directory. Do not store files directly at the top-level of the Library directory. Instead, store them in one of the specific subdirectories described in this table. In OS X v10.7 and later, the Finder hides the Library directory in the user’s home folder by default. Therefore, you should never store files in this directory that you want the user to access. To get the path to this directory use the NSLibraryDirectory search path key with the NSUserDomainMask domain. Library directory The Mac Application Environment Low-Level Details of the Runtime Environment 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 14Directory Description The Application Support directory is where your app stores any type of file thatsupports the app but is not required for the app to run, such as document templates or configuration files. The files should be app-specific but should never store user data. This directory is located inside the Library directory. Never store files at the top level of this directory: Always put them in a subdirectory named for your app or company. If the resources apply to all users on the system, such as document templates, place them in /Library/Application Support. To get the path to this directory use the NSApplicationSupportDirectory search path key with the NSLocalDomainMask domain. If the resources are user-specific, such as workspace configuration files, place them in the current user’s ~/Library/Application Support directory. To get the path to this directory use the NSApplicationSupportDirectory search path key with the NSUserDomainMask domain. Application Support directory The Caches directory is where you store cache files and other temporary data that your app can re-create as needed. This directory is located inside the Library directory. Never store files at the top level of this directory: Always put them in a subdirectory named for your app or company. Your app is responsible for cleaning out cache data files when they are no longer needed. The system does not delete files from this directory. To get the path to this directory use the NSCachesDirectory search path key with the NSUserDomainMask domain. Caches directory The Movies directory contains the user’s video files. To get the path to this directory use the NSMoviesDirectory search path key with the NSUserDomainMask domain. Movies directory The Music directory contains the user’s music and audio files. To get the path to this directory use the NSMusicDirectory search path key with the NSUserDomainMask domain. Music directory The Pictures directory contains the user’s images and photos. To get the path to this directory use the NSPicturesDirectory search path key with the NSUserDomainMask domain. Pictures directory The Mac Application Environment Low-Level Details of the Runtime Environment 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 15Directory Description The Temporary directory is where you store files that do not need to persist between launches of your app. You normally use this directory for scratch files or other types ofshort-lived data filesthat are not related to your app’s persistent data. This directory is typically hidden from the user. Your app should remove files from this directory as soon as it is done with them. The system may also purge lingering files from this directory at system startup. To get the path to this directory use the NSTemporaryDirectory function. Temporary directory Listing 1-1 shows an example of how to retrieve the base path to the Application Support directory and then append a custom app directory to it. Listing 1-1 Getting the path to the Application Support directory NSFileManager* fileManager = [NSFileManager defaultManager]; NSURL* appSupportDir = nil; NSArray *urls = [fileManager URLsForDirectory:NSApplicationSupportDirectory inDomains:NSUserDomainMask]; if ([paths count] > 0) { appSupportDir = [[urls objectAtIndex:0] URLByAppendingPathComponent:@"com.example.MyApp"]; } For more information about how to access files in well known system directories, see File System Programming Guide . Coordinating File Access with Other Processes In OS X, other processes may have access to the same files that your app does. Therefore, when working with files, you should use the file coordination interfacesintroduced in OS X v10.7 to be notified when other processes (including the Finder) attempt to read or modify files your app is currently using. For example, coordinating file access is critical when your app adopts iCloud storage. The file coordination APIs allow you to assert ownership over files and directories that your app cares about. Any time another process attempts to touch one of those items, your app is given a chance to respond. For example, when an app attemptsto read the contents of a document your app is editing, you can write unsaved changes to disk before the other process is allowed to do its reading. The Mac Application Environment Low-Level Details of the Runtime Environment 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 16Using iCloud document storage, for example, you must incorporate file coordination because multiple apps can access your document files in iCloud. The simplest way to incorporate file coordination into your app is to use the NSDocument class, which handles all of the file-related management for you. See Document-Based App Programming Guide for Mac . On the other hand, if you're writing a library-style (or “shoebox”) app, you must use the file coordination interfaces directly, as described in File System Programming Guide . Interacting with the File System Disks in Macintosh computers are formatted using the HFS+ file system by default. However, Macintosh computers can interact with disks that use other formats so you should never code specifically to any one file system. Table 1-2 lists some of the basic file system attributes you may need to consider in your app and how you should handle them. Table 1-2 Attributes for the OS X file system Attribute Description The HFS+ file system is case-insensitive but also case-preserving. Therefore, when specifying filenames and directoriesin your code, it is best to assume case-sensitivity. Case sensitivity Construct paths using the methods of the NSURL and NSString classes. The NSURL classis preferred for path construction because of its ability to specify not only paths in the local file system but paths to network resources. Path construction Many file-related attributes can be retrieved using the getResourceValue: forKey:error: method of the NSURL class. You can also use an NSFileManager object to retrieve many file-related attributes. File attributes File permissions are managed using access control lists(ACLs) and BSD permissions. The system uses ACLs whenever possible to specify precise permissionsfor files and directories, but it falls back to using BSD permissions when no ACLs are specified. By default, any files your app creates are owned by the current user and given appropriate permissions. Thus, your app should always be able to read and write files it creates explicitly. In addition, the app’s sandbox may allow it to access other filesin specific situations. For more information about the sandbox,see “App Sandbox and XPC” (page 18). File permissions Appsthat cannot use the File Coordination interfaces(see “Coordinating File Access with Other Processes” (page 16)) to track changes to files and directories can use the FSEvents API instead. This API provides a lower-level interface for tracking file system interactions and is available in OS X v10.5 and later. For information on how to use the FSEvents API,see File SystemEvents Programming Guide . Tracking file changes The Mac Application Environment Low-Level Details of the Runtime Environment 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 17Security The security technologies in OS X help you safeguard sensitive data created or managed by your app, and help minimize damage caused by successful attacks from hostile code. These technologies impact how your app interacts with system resources and the file system. App Sandbox and XPC You secure your app against attack from malware by following the practices recommended in Secure Coding Guide . But an attacker needs only to find a single hole in your defenses, or in any of the frameworks and libraries that you link against, to gain control of your app along with all of its privileges. Starting in OS X v10.7, App Sandbox provides a last line of defense against stolen, corrupted, or deleted user data if malicious code exploits your app. App Sandbox also minimizes the damage from coding errors. Its strategy is twofold: 1. App Sandbox enables you to describe how your app interacts with the system. The system then grants your app the access it needs to get its job done, and no more. For your app to provide the highest level of damage containment, the best practice is to adopt the tightest sandbox possible. 2. App Sandbox allows the user to transparently grant your app additional access by way of Open and Save dialogs, drag and drop, and other familiar user interactions. You describe your app’s interaction with the system by way of setting entitlements in Xcode. An entitlement is a key-value pair, defined in a property list file, that confers a specific capability or security permission to a target. For example, there are entitlement keys to indicate that your app needs access to the camera, the network, and user data such as the Address Book. For details on all the entitlements available in OS X, see Entitlement Key Reference . When you adopt App Sandbox, the system provides a special directory for use by your app—and only by your app—called a container. Your app has unfettered read/write access to the container. All OS X path-finding APIs, above the POSIX layer, are relative to the container instead of to the user’s home directory. Othersandboxed apps have no access to your app’s container, as described further in “Code Signing” (page 19). The Mac Application Environment Low-Level Details of the Runtime Environment 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 18iOS Note: Because it is not for user documents, an OS X container differs from an iOS container which, in iOS, is the one and only location for user documents. As the sole local location for user documents, an iOS container is usually known simply as an app’s Documents directory. In addition, an iOS container contains the app itself. This is not so in OS X. iCloud Note: Apple’s iCloud technology, as described in “iCloud Storage”, uses the name “container” as well. There is no functional connection between an iCloud container and an App Sandbox container. Your sandboxed app can access paths outside of its container in the following three ways: ● At the specific direction of the user ● By you configuring your app with entitlements for specific file-system locations, such as the Movies folder ● When a path is in any of certain directories that are world readable The OS X security technology that interacts with the user to expand yoursandbox is called Powerbox. Powerbox has no API. Your app uses Powerbox transparently when, for example, you use the NSOpenPanel and NSSavePanel classes, or when the user employs drag and drop with your app. Some app operations are more likely to be targets of malicious exploitation. Examples are the parsing of data received over a network, and the decoding of video frames. By using XPC, you can improve the effectiveness of the damage containment offered by App Sandbox by separating such potentially dangerous activities into their own address spaces. XPC is an OS X interprocess communication technology that complements App Sandbox by enabling privilege separation. Privilege separation, in turn, is a development strategy in which you divide an app into pieces according to the system resource access that each piece needs. The component pieces that you create are called XPC services. For details on adopting XPC, see Daemons and Services Programming Guide . For a complete explanation of App Sandbox and how to use it, read App Sandbox Design Guide . Code Signing OS X employs the security technology known as code signing to allow you to certify that your app was indeed created by you. After an app is code signed, the system can detect any change to the app—whether the change is introduced accidentally or by malicious code. Various security technologies, including App Sandbox and parental controls, depend on code signing. The Mac Application Environment Low-Level Details of the Runtime Environment 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 19In most cases, you can rely on Xcode’s automatic code signing, which requires only that you specify a code signing identity in the build settings for your project. The steps to take are described in “Code Signing Your App” in Tools Workflow Guide for Mac . If you need to incorporate code signing into an automated build system, or if you link your app against third-party frameworks, refer to the procedures described in Code Signing Guide . When you adopt App Sandbox, you must code sign your app. This is because entitlements (including the special entitlement that enables App Sandbox) are built into an app’s code signature. OS X enforces a tie between an app’s container and the app’s code signature. This important security feature ensures that no other sandboxed app can access your container. The mechanism works as follows: After the system creates a container for an app, each time an app with the same bundle ID launches, the system checks that the app’s code signature matches a code signature expected by the container. If the system detects a mismatch, it prevents the app from launching. For a complete explanation of code signing in the context of App Sandbox, read “App Sandbox in Depth” in App Sandbox Design Guide . The Keychain A keychain is a secure, encrypted container for storing a user’s passwords and other secrets. It is designed to help a user manage their multiple logins, each with its own ID and password. You should always use keychain to store sensitive credentials for your app. For more on the keychain, see “Keychain Services Concepts” in Keychain Services Programming Guide . The Mac Application Environment Low-Level Details of the Runtime Environment 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 20To unleash the power of OS X, you develop apps using the Cocoa application environment. Cocoa presents the app’s user interface and integrates it tightly with the other components of the operating system. Cocoa provides an integrated suite of object-oriented software components packaged in two core class libraries, the AppKit and Foundation frameworks, and a number of underlying frameworks providing supporting technologies. Cocoa classes are reusable and extensible—you can use them as is or extend them for your particular requirements. Cocoa makes it easy to create apps that adopt all of the conventions and expose all of the power of OS X. In fact, you can create a new Cocoa application project in Xcode and, without adding any code, have a functional app. Such an app is able to display its window (or create new documents) and implements many standard system behaviors. And although the Xcode templates provide some code to make this all happen, the amount of code they provide is minimal. Most of the behavior is provided by Cocoa itself. To make a great app, you should build on the foundations Cocoa lays down for you, working with the conventions and infrastructure provided for you. To do so effectively, it'simportant to understand how a Cocoa app fits together. Fundamental Design Patterns Cocoa incorporates many design patterns in its implementation. Table 2-1 lists the key design patterns with which you should be familiar. Table 2-1 Fundamental design patterns used by Mac apps Design pattern Why it is important Use of the Model-View-Controller (MVC) design pattern ensures that the objects you create now can be reused or updated easily in future versions of your app. Cocoa provides most of the classes used to build your app’s controller and view layers. It is your job to customize the classes you need and provide the necessary data model objects to go with them. MVC is central to a good design for a Cocoa application because many Cocoa technologies and architectures are based on MVC and require that your custom objects assume one of the MVC roles. Model-View-Controller 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 21 The Core App DesignDesign pattern Why it is important The delegation design pattern allows you to change the runtime behavior of an object without subclassing. Delegate objects conform to a specific protocol that defines the interaction points between the delegate and the object it modifies. Atspecific points, the master object callsthe methods of its delegate to provide it with information or ask what to do. The delegate can then take whatever actions are appropriate. Delegation The responder chain definesthe relationships between event-handling objects in your app. As events arrive, the app dispatches them to the first responder object for handling. If that object does not want the event, it passes it to the next responder, which can either handle the event or send it to its next responder, and so on up the chain. Windows and views are the most common types of responder objects and are always the first responders for mouse events. Other types of objects, such as your app’s controller objects, may also be responders. Responder chain Controls use the target-action design pattern to notify your app of user interactions. When the user interacts with a control in a predefined way (such as by touching a button), the controlsends a message (the action) to an object you specify (the target). Upon receiving the action message, the target object can then respond in an appropriate manner. Target-action Block objects are a convenient way to encapsulate code and local stack variablesin a form that can be executed later. Blocks are used in lieu of callback functions by many frameworks and are also used in conjunction with Grand Central Dispatch to perform tasks asynchronously. For more information about using blocks, see Blocks Programming Topics. Block objects Notifications are used throughout Cocoa to deliver news of changes to your app. Many objects send notifications at key moments in the object’s life cycle. Intercepting these notifications gives you a chance to respond and add custom behavior. Notifications KVO tracks changes to a specific property of an object. When that property changes, the change generates automatic notifications for any objects that registered an interest in that property. Those observers then have a chance to respond to the change. Key-value observing (KVO) The Core App Design Fundamental Design Patterns 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 22Design pattern Why it is important Cocoa bindings provide a convenient bridge between the model, view, and controller portions of your app. You bind a view to some underlying data object (which can be static or dynamic) through one of your controllers. Changes to the view are then automatically reflected in the data object, and vice versa. The use of bindings is not required for apps but does minimize the amount of code you have to write. You can set up bindings programmatically or using Interface Builder. Bindings For a more detailed discussion of Cocoa and the design patterns you use to implement Mac apps, see Cocoa Fundamentals Guide . The App Style Determines the Core Architecture The style of your app defines which core objects you must use in its implementation. Cocoa supports the creation of both single-window and multiwindow apps. For multiwindow designs, it also provides a document architecture to help manage the files associated with each app window. Thus, apps can have the following forms: ● Single-window utility app ● Single-window library-style app ● Multiwindow document-based app You should choose a basic app style early in your design process because that choice affects everything you do later. The single-window styles are preferred in many cases, especially for developers bringing apps from iOS. The single-window style typically yields a more streamlined user experience, and it also makes it easier for your app to support a full-screen mode. However, if your app works extensively with complex documents, the multiwindow style may be preferable because it provides more document-related infrastructure to help you implement your app. The Core App Design The App Style Determines the Core Architecture 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 23The Calculator app provided with OS X, shown in Figure 2-1, is an example of a single-window utility app. Utility apps typically handle ephemeral data or manage system processes. Calculator does not create or deal with any documents or persistent user data but simply processes numerical data entered by the user into the text field in its single window, displaying the results of its calculations in the same field. When the user quits the app, the data it processed is simply discarded. Figure 2-1 The Calculator single-window utility app Single-window, library-style (or “shoebox”) apps do handle persistent user data. One of the most prominent examples of a library-style app is iPhoto, shown in Figure 2-2. The user data handled by iPhoto are photos (and associated metadata), which the app edits, displays, and stores. All user interaction with iPhoto happens in a single window. Although iPhoto stores its data in files, it doesn’t present the files to the user. The app presents a simplified interface so that users don’t need to manage files in order to use the app. Instead, they work directly with their photos. Moreover, iPhoto hides its files from regular manipulation in the Finder by placing The Core App Design The App Style Determines the Core Architecture 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 24them within a single package. In addition, the app savesthe user’s editing changesto disk at appropriate times. So, users are relieved of the need to manually save, open, or close documents. This simplicity for users is one of the key advantages of the library-style app design. Figure 2-2 The iPhoto single-window app A good example of a multiwindow document-based app is TextEdit, which creates, displays, and edits documents containing plain or styled text and images. TextEdit does not organize or manage its documents—users do that with the Finder. Each TextEdit document opens in its own window, multiple documents can be open at The Core App Design The App Style Determines the Core Architecture 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 25one time, and the user interacts with the frontmost document using controls in the window’s toolbar and the app’s menu bar. Figure 2-3 shows a document created by TextEdit. For more information about the document-based app design, see “Document-Based Apps Are Based on an NSDocument Subclass” (page 31). Figure 2-3 TextEdit document window Both single-window and multiwindow apps can present an effective full-screen mode, which provides an immersive experience that enables users to focus on their tasks without distractions. For information about full-screen mode, see “Implementing the Full-Screen Experience” (page 49). The Core Objects for All Cocoa Apps Regardless of whether you are using a single-window or multiwindow app style, all apps use the same core set of objects. Cocoa provides the default behavior for most of these objects. You are expected to provide a certain amount of customization of these objects to implement your app’s custom behavior. The Core App Design The App Style Determines the Core Architecture 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 26Figure 2-4 shows the relationships among the core objects for the single-window app styles. The objects in this figure are separated according to whether they are part of the model, view, or controller portions of the app. As you can see from the figure, the Cocoa–provided objects provide much of the controller and view layer for your app. Figure 2-4 Key objects in a single-window app Table 2-2 (page 27) describes the roles played by the objects in the diagram. Table 2-2 The core objects used by all Cocoa apps Object Description (Required) Runs the event loop and manage interactions between your app and the system. You typically use the NSApplication class as is, putting any custom app-object-related code in your application delegate object. NSApplication object (Expected) A custom object that you provide which works closely with the NSApplication object to run the app and manage the transitions between different application states. Your application delegate object must conform to the NSApplicationDelegate Protocol. Application delegate object The Core App Design The App Style Determines the Core Architecture 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 27Object Description Store content specific to your app. A banking app might store a database containing financial transactions, whereas a painting app might store an image object or the sequence of drawing commands that led to the creation of that image. Data model objects Responsible for loading and managing a single window each and coordinating with the system to handle standard window behaviors. You subclass NSWindowController tomanage both the window and its contents. Each window controller is responsible for everything that happens in its window. If the contents of your window are simple, the window controller may do all of the management itself. If your window is more complex, the window controller might use one or more view controllers to manage portions of the window. Window controllers Represent your onscreen windows, configured in different styles depending on your app’s needs. For example, most windows have title bars and borders but you can also configure windows without those visual adornments. A window object is almost always managed by a window controller. An app can also have secondary windows, also known as dialogs and panels. These windows are subordinate to the current document window or, in the case of single-window apps, to the main window. They support the document or main window, for example, allowing selection of fonts and color, allowing the selection of tools from a palette, or displaying a warning‚ A secondary window is often modal. Window objects Coordinate the loading of a single view hierarchy into your app. Use view controllersto divide up the work for managing more sophisticated window layouts. Your view controllers work together (with the window controller) to present the window contents. If you have developed iOS apps, be aware that AppKit view controllers play a less prominent role than UIKit view controllers. In OS X, AppKit view controllers are assistantsto the window controller, which is ultimately responsible for everything that goes in the window. The main job of an AppKit view controller is to load its view hierarchy. Everything else is custom code that you write. View controllers Define a rectangular region in a window, draw the contents of that region, and handle events in that region. Views can be layered on top of each other to create view hierarchies, whereby one view obscures a portion of the underlying view. View objects Representstandard system controls. These view subclasses provide standard visual items such as buttons, text fields, and tables that you can use to build your user interface. Although a few controls are used as is to present visual adornments, most work with your code to manage user interactions with your app’s content. Control objects The Core App Design The App Style Determines the Core Architecture 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 28Additional Core Objects for Multiwindow Apps As opposed to a single-window app, a multiwindow app uses several windows to present its primary content. The Cocoa support for multiwindow appsis built around a document-based model implemented by a subsystem called the document architecture. In this model, each document object manages its content, coordinates the reading and writing of that content from disk, and presents the content in a window for editing. All document objects work with the Cocoa infrastructure to coordinate event delivery and such, but each document object is otherwise independent of its fellow document objects. Figure 2-5 shows the relationships among the core objects of a multiwindow document-based app. Many of the same objects in this figure are identical to those used by a single-window app. The main difference is the insertion of the NSDocumentController and NSDocument objects between the application objects and the objects for managing the user interface. Figure 2-5 Key objects in a multiwindow document app Table 2-3 (page 30) describes the role of the inserted NSDocumentController and NSDocument objects. (For information about the roles of the other objects in the diagram, see Table 2-2 (page 27).) The Core App Design The App Style Determines the Core Architecture 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 29Table 2-3 Additional objects used by multiwindow document apps Object Description The NSDocumentController class defines a high-level controller for creating and managing all document objects. In addition to managing documents, the document controller also manages many document-related menu items, such as the Open Recent menu and the open and save panels. Document Controller object The NSDocument class is the base class for implementing documents in a multiwindow app. This class acts as the controller for the data objects associated with the document. You define your own custom subclasses to manage the interactions with your app’s data objects and to work with one or more NSWindowController objectsto display the document contents on the screen. Document object Integrating iCloud Support Into Your App No matter how you store your app’s data, iCloud is a convenient way to make that data available to all of a user’s devices. To integrate iCloud into your app, you change where you store user files. Instead of storing them in the user’s Home folder or in your App Sandbox container, you store them in special file system locations known as ubiquity containers. A ubiquity containerserves asthe local representation of corresponding iCloud storage. It is outside of your App Sandbox container, and so requires specific entitlements for your app to interact with it. In addition to a change in file system locations, your app design needs to acknowledge that your data model is accessible to multiple processes. The following considerations apply: ● Document-based apps get iCloud support through the NSDocument class, which handles most of the interactions required to manage the on-disk file packages that represent documents. ● If you implement a custom data model and manage files yourself, you must explicitly use file coordination to ensure that the changes you make are done safely and in concert with the changes made on the user’s other devices. For details,see “The Role of File Coordinators and Presenters” in File System Programming Guide . ● For storing small amounts of data in iCloud, you use key-value storage. Use key-value storage for such things as stocks or weather information, locations, bookmarks, a recent-documents list, settings and preferences, and simple game state. Every iCloud app should take advantage of key-value storage. To interact with key-value storage, you use the shared NSUbiquitousKeyValueStore object. To learn how to adopt iCloud in your app, read iCloud Design Guide . The Core App Design The App Style Determines the Core Architecture 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 30Shoebox-Style Apps Should Not Use NSDocument When implementing a single-window, shoebox-style (sometimes referred to as a “library” style) app, it is sometimes better not to use NSDocument objectsto manage your content. The NSDocument class was designed specifically for use in multiwindow document apps. Instead, use custom controller objects to manage your data. Those custom controllers would then work with a view controller or your app’s main window controller to coordinate the presentation of the data. Although you normally use an NSDocumentController object only in multiwindow apps, you can subclass it and use it in a single-window app to coordinate the Open Recent and similar behaviors. When subclassing, though, you must override any methods related to the creation of NSDocument objects. Document-Based Apps Are Based on an NSDocument Subclass Documents are containers for user data that can be stored in files and iCloud. In a document-based design, the app enables users to create and manage documents containing their data. One app typically handles multiple documents, each in its own window, and often displays more than one document at a time. For example, a word processor provides commands to create new documents, it presents an editing environment in which the user enters text and embeds graphics into the document, it saves the document data to disk (and, optionally, iCloud), and it provides other document-related commands, such as printing and version management. In Cocoa, the document-based app design is enabled by the document architecture, which is part of of the AppKit framework. Documents in OS X There are several waysto think of a document. Conceptually, a document is a container for a body of information that can be named and stored in a disk file and in iCloud. In this sense, the document is not the same as the file but is an object in memory that owns and manages the document data. To users, the document is their information—such as text and graphics formatted on a page. Programmatically, a document is an instance of a custom NSDocument subclass that knows how to represent internally persistent data that it can display in windows. This document object knows how to read document data from a file and create an object graph in The Core App Design Document-Based Apps Are Based on an NSDocument Subclass 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 31memory for the document data model. It also knows how to handle the user’s editing commands to modify the data model and write the document data back out to disk. So, the document object mediates between different representations of document data, as shown in Figure 2-6. Figure 2-6 Document file, object, and data model Using iCloud, documents can be shared automatically among a user’s computers and iOS devices. Changes to the document data are synchronized without user intervention. For information about iCloud, see “Integrating iCloud Support Into Your App” (page 30). The Document Architecture Provides Many Capabilities for Free The document-based style of app is a design choice that you should consider when you design your app. If it makes sense for your users to create multiple discrete sets of data, each of which they can edit in a graphical environment and store in files or iCloud, then you certainly should plan to develop a document-based app. The Cocoa document architecture provides a framework for document-based apps to do the following things: ● Create new documents. The first time the user chooses to save a new document, it presents a dialog enabling the user to name and save the document in a disk file in a user-chosen location. ● Open existing documents stored in files. A document-based app specifies the types of document it can read and write, as well as read-only and write-only types. It can represent the data of different types internally and display the data appropriately. It can also close documents. ● Automatically save documents. Document-based apps can adopt autosaving in place, and its documents are automatically saved at appropriate times so that the data the user sees on screen is effectively the same as that saved on disk. Saving is done safely, so that an interrupted save operation does not leave data inconsistent. The Core App Design Document-Based Apps Are Based on an NSDocument Subclass 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 32● Asynchronously read and write document data. Reading and writing are done asynchronously on a background thread, so that lengthy operations do not make the app’s user interface unresponsive. In addition, reads and writes are coordinated using NSFilePresenter protocol and NSFileCoordinator class to reduce version conflicts. Coordinated reads and writes reduce version conflicts both among different appssharing document data in localstorage and among different instances of an app on different devices sharing document data via iCloud. ● Manage multiple versions of documents. Autosave creates versions at regular intervals, and users can manually save a version whenever they wish. Users can browse versions and revert the document’s contents to a chosen version using a Time Machine–like interface. The version browser is also used to resolve version conflicts from simultaneous iCloud updates. ● Print documents. The print dialog and page setup dialog enable the user to choose various page layouts. ● Monitor and set the document’s edited status and validate menu items. To avoid automatic saving of inadvertent changes, old files are locked from editing until explicitly unlocked by the user. ● Track changes. The document manages its edited status and implements multilevel undo and redo. ● Handle app and window delegation. Notifications are sent and delegate methods called at significant lifecycle events, such as when the app terminates. See Document-Based App Programming Guide for Mac for more detailed information about how to implement a document-based app. The App Life Cycle The app life cycle is the progress of an app from its launch through its termination. Apps can be launched by the user or the system. The user launches apps by double-clicking the app icon, using Launchpad, or opening a file whose type is currently associated with the app. In OS X v10.7 and later, the system launches apps at user login time when it needs to restore the user’s desktop to its previous state. When an app is launched, the system creates a process and all of the normal system-related data structures for it. Inside the process, it creates a main thread and uses it to begin executing your app’s code. At that point, your app’s code takes over and your app is running. The main Function is the App Entry Point Like any C-based app, the main entry point for a Mac app at launch time is the main function. In a Mac app, the main function is used only minimally. Its main job is to give control to the AppKit framework. Any new project you create in Xcode comes with a default main function like the one shown in Listing 2-1. You should normally not need to change the implementation of this function. The Core App Design The App Life Cycle 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 33Listing 2-1 The main function of a Mac app #import int main(int argc, char *argv[]) { return NSApplicationMain(argc, (const char **) argv); } The NSApplicationMain function initializes your app and prepares it to run. As part of the initialization process, this function does several things: ● Creates an instance of the NSApplication class. You can access this object from anywhere in your app using the sharedApplication class method. ● Loads the nib file specified by the NSMainNibFile key in the Info.plist file and instantiates all of the objects in that file. This is your app’s main nib file and should contain your application delegate and any other critical objects that must be loaded early in the launch cycle. Any objects that are not needed at launch time should be placed in separate nib files and loaded later. ● Calls the run method of your application object to finish the launch cycle and begin processing events. By the time the run method is called, the main objects of your app are loaded into memory but the app is still not fully launched. The run method notifies the application delegate that the app is about to launch, shows the application menu bar, opens any files that were passed to the app, does some framework housekeeping, and starts the event processing loop. All of this work occurs on the app’s main thread with one exception. Files may be opened in secondary threads if the canConcurrentlyReadDocumentsOfType: class method of the corresponding NSDocument object returns YES. If your app preserves its user interface between launch cycles, Cocoa loads any preserved data at launch time and uses it to re-create the windows that were open the last time your app was running. For more information about how to preserve your app’s user interface, see “User Interface Preservation” (page 39). The App’s Main Event Loop Drives Interactions Asthe user interacts with your app, the app’s main event loop processesincoming events and dispatchesthem to the appropriate objects for handling. When the NSApplication object is first created, it establishes a connection with the system window server, which receives events from the underlying hardware and transfers The Core App Design The App Life Cycle 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 34them to the app. The app also sets up a FIFO event queue to store the events sent to it by the window server. The main event loop isthen responsible for dequeueing and processing events waiting in the queue, asshown in Figure 2-7. Figure 2-7 The main event loop The run method of the NSApplication object is the workhorse of the main event loop. In a closed loop, this method executes the following steps until the app terminates: 1. Services window-update notifications, which results in the redrawing of any windows that are marked as “dirty.” 2. Dequeues an event from its internal event queue using the nextEventMatchingMask:untilDate:inMode:dequeue: method and converts the event data into an NSEvent object. 3. Dispatchesthe event to the appropriate target object using the sendEvent: method of NSApplication. When the app dispatches an event, the sendEvent: method uses the type of the event to determine the appropriate target. There are two major types of input events: key events and mouse events. Key events are sent to the key window—the window that is currently accepting key presses. Mouse events are dispatched to the window in which the event occurred. For mouse events, the window looks for the view in which the event occurred and dispatches the event to that object first. Views are responder objects and are capable of responding to any type of event. If the view is a control, it typically uses the event to generate an action message for its associated target. The overall process for handling events is described in detail in Cocoa Event Handling Guide . The Core App Design The App Life Cycle 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 35Automatic and Sudden Termination of Apps Improve the User Experience In OS X v10.7 and later, the use of the Quit command to terminate an app is diminished in favor of more user-centric techniques. Specifically, Cocoa supports two techniques that make the termination of an app transparent and fast: ● Automatic termination eliminates the need for users to quit an app. Instead, the system manages app termination transparently behind the scenes, terminating apps that are not in use to reclaim needed resources such as memory. ● Sudden termination allows the system to kill an app’s process immediately without waiting for it to perform any final actions. The system uses this technique to improve the speed of operations such as logging out of, restarting, or shutting down the computer. Automatic termination and sudden termination are independent techniques, although both are designed to improve the user experience of app termination. Although Apple recommendsthat appssupport both, an app can support one technique and not the other. Apps that support both techniques can be terminated by the system without the app being involved at all. On the other hand, if an app supports sudden termination but not automatic termination, then it must be sent a Quit event, which it needs to process without displaying any user interface dialogs. Automatic termination transfers the job of managing processes from the user to the system, which is better equipped to handle the job. Users do not need to manage processes manually anyway. All they really need is to run apps and have those apps available when they need them. Automatic termination makes that possible while ensuring that system performance is not adversely affected. Apps must opt in to both automatic termination and sudden termination and implement appropriate support for them. In both cases, the app must ensure that any user data is saved well before termination can happen. And because the user does not quit an autoterminable app, such an app should also save the state of its user interface using the built-in Cocoa support. Saving and restoring the interface state provides the user with a sense of continuity between app launches. For information on how to support for automatic termination in your app, see “Automatic Termination” (page 37). For information on how to support sudden termination, see “Sudden Termination” (page 38). Support the Key Runtime Behaviors in Your Apps No matter what style of app you are creating, there are specific behaviors that all apps should support. These behaviors are intended to help users focus on the content they are creating rather than focus on app management and other busy work that is not part of creating their content. The Core App Design Support the Key Runtime Behaviors in Your Apps 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 36Automatic Termination Automatic termination is a feature that you must explicitly code for in your app. Declaring support for automatic termination is easy, but apps also need to work with the system to save the current state of their user interface so that it can be restored later as needed. The system can kill the underlying process for an auto-terminable app at any time, so saving this information maintains continuity for the app. Usually, the system kills an app’s underlying process some time after the user has closed all of the app’s windows. However, the system may also kill an app with open windows if the app is not currently on screen, perhaps because the user hid it or switched spaces. To support automatic termination, you should do the following: ● Declare your app’s support for automatic termination, either programmatically or using an Info.plist key. ● Support saving and restoring your window configurations. ● Save the user’s data at appropriate times. ● Single-window, library-style apps should implement strategies for saving data at appropriate checkpoints. ● Multiwindow, document-based apps can use the autosaving and saveless documents capabilities in NSDocument. ● Whenever possible, support sudden termination for your app as well. Enabling Automatic Termination in Your App Declaring support for automatic termination letsthe system know that itshould manage the actual termination of your app at appropriate times. An app has two ways to declare its support for automatic termination: ● Include the NSSupportsAutomaticTermination key (with the value YES) in the app’s Info.plist file. This sets the app’s default support status. ● Use the NSProcessInfo classto declare support for automatic termination dynamically. Use thistechnique to change the default support of an app that includes the NSSupportsAutomaticTermination key in its Info.plist file. Automatic Data-Saving Strategies Relieve the User You should always avoid forcing the user to save changesto their data manually. Instead, implement automatic data saving. For a multiwindow app based on NSDocument, automatic saving is as simple as overriding the autosavesInPlace classmethod to return YES. Formore information,seeDocument-Based App Programming Guide for Mac . The Core App Design Support the Key Runtime Behaviors in Your Apps 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 37For a single-window, library-style app, identify appropriate pointsin your code where any user-related changes should be saved and write those changes to disk automatically. This benefits the user by eliminating the need to think about manually saving changes, and when done regularly, it ensures that the user does not lose much data if there is a problem. Some appropriate times when you can save user data automatically include the following: ● When the user closes the app window or quits the app (applicationWillTerminate:) ● When the app is deactivated (applicationWillResignActive:) ● When the user hides your app (applicationWillHide:) ● Whenever the user makes a valid change to data in your app The last item means that you have the freedom to save the user’s data at any time it makes sense to do so. For example, if the user is editing fields of a data record, you can save each field value as it is changed or you can wait and save all fields when the user displays a new record. Making these types of incremental changes ensures that the data is always up-to-date but also requires more fine-grained management of your data model. In such an instance, Core Data can help you make the changes more easily. For information about Core Data, see Core Data Starting Point. Sudden Termination Sudden termination lets the system know that your app’s process can be killed directly without any additional involvement from your app. The benefit of supporting sudden termination is that it lets the system close apps more quickly, which is important when the user is shutting down a computer or logging out. An app has two ways to declare its support for sudden termination: ● Include the NSSupportsSuddenTermination key (with the value YES) in the app’s Info.plist file. ● Use the NSProcessInfo class to declare support for sudden termination dynamically. You can also use this class to change the default support of an app that includes the NSSupportsSuddenTermination key in its Info.plist file. One solution is to declare global support for the feature globally and then manually override the behavior at appropriate times. Because sudden termination means the system can kill your app at any time after launch, you should disable it while performing actions that might lead to data corruption if interrupted. When the action is complete, reenable the feature again. The Core App Design Support the Key Runtime Behaviors in Your Apps 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 38You disable and enable sudden termination programmatically using the disableSuddenTermination and enableSuddenTerminationmethods ofthe NSProcessInfo class. Thesemethodsincrement and decrement a counter, respectively, maintained by the process. When the value of this counter is 0, the process is eligible for sudden termination. When the value is greater than 0, sudden termination is disabled. Enabling and disabling sudden termination dynamically also meansthat your app should save data progressively and not rely solely on user actions to save important information. The best way to ensure that your app’s information is saved at appropriate times is to support the interfaces in OS X v10.7 for saving your document and window state. Those interfaces facilitate the automatic saving of relevant user and app data. For more information about saving your user interface state, see “User Interface Preservation” (page 39). For more information about saving your documents, see “Document-Based Apps Are Based on an NSDocument Subclass” (page 31). For additional information about enabling and disabling sudden termination,see NSProcessInfo Class Reference . User Interface Preservation The Resume feature, in OS X v10.7 and later, saves the state of your app’s windows and restores them during subsequent launches of your app. Saving the state of your windows enables you to return your app to the state it was in when the user last used it. Use the Resume feature especially if your app supports automatic termination, which can cause your app to be terminated while it is running but hidden from the user. If your app supports automatic termination but does not preserve its interface, the app launches into its default state. Users who only switched away from your app might think that the app crashed while it was not being used. Writing Out the State of Your Windows and Custom Objects You must do the following to preserve the state of your user interface: ● For each window, you must set whether the window should be preserved using the setRestorable: method. ● For each preserved window, you must specify an object whose job is to re-create that window at launch time. ● Any objects involved in your user interface must write out the data they require to restore their state later. ● At launch time, you must use the provided data to restore your objects to their previous state. The actual process of writing out your application state to disk and restoring it later is handled by Cocoa, but you must tell Cocoa what to save. Your app’s windows are the starting point for all save operations. Cocoa iterates over all of your app’s windows and saves data for the ones whose isRestorable method returns YES. Most windows are preserved by default, but you can change the preservation state of a window using the setRestorable: method. The Core App Design Support the Key Runtime Behaviors in Your Apps 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 39In addition to preserving your windows, Cocoa saves data for most of the responder objects associated with the window. Specifically, it saves the views and window controller objects associated with the window. (For a multiwindow document-based app, the window controller also saves data from its associated document object.) Figure 2-8 shows the path that Cocoa takes when determining which objects to save. Window objects are always the starting point, but other related objects are saved, too. Figure 2-8 Responder objects targeted by Cocoa for preservation All Cocoa window and view objects save basic information about their size and location, plus information about other attributes that might affect the way they are currently displayed. For example, a tab view saves the index of the selected tab, and a text view savesthe location and range of the current textselection. However, these responder objects do not have any inherent knowledge about your app’s data structures. Therefore, it is your responsibility to save your app’s data and any additional information needed to restore the window to its current state. There are several places where you can write out your custom state information: ● If you subclass NSWindow or NSView, implement the encodeRestorableStateWithCoder: method in your subclass and use it to write out any relevant data. Alternatively, your custom responder objects can override the restorableStateKeyPaths method and use it to specify key paths for any attributes to be preserved. Cocoa uses the key paths to locate and save the data for the corresponding attribute. Attributes must be compliant with key-value coding and Key-value observing. ● If your window has a delegate object, implement the window:willEncodeRestorableState: method for the delegate and use it to store any relevant data. ● In your window controller, use the encodeRestorableStateWithCoder: method to save any relevant data or configuration information. The Core App Design Support the Key Runtime Behaviors in Your Apps 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 40Be judicious when deciding what data to preserve, and strive to write out the smallest amount of information that is required to reconfigure your window and associated objects. You are expected to save the actual data that the window displays and enough information to reattach the window to the same data objects later. Important: Never use the user interface preservation mechanism as a way to save your app’s actual data. The archive created for interface preservation can change frequently and may be ignored altogether if there is a problem during the restoration process. Your app data should always be saved independently in data files that are managed by your app. For information on how to use coder objects to archive state information, see NSCoder Class Reference . For additional information on what you need to do to save state in a multiwindow document-based app, see Document-Based App Programming Guide for Mac . Notifying Cocoa About Changes to Your Interface State Whenever the preserved state of one of your responder objects changes, mark the object as dirty by calling the invalidateRestorableState method of that object. Having done so, at some point in the future, encodeRestorableStateWithCoder: message is sent to your responder object. Marking your responder objects as dirty lets Cocoa know that it needs to write their preservation state to disk at an appropriate time. Invalidating your objects is a lightweight operation in itself because the data is not written to disk right away. Instead, changes are coalesced and written at key times, such as when the user switches to another app or logs out. You should mark a responder object as dirty only for changes that are truly interface related. For example, a tab view marks itself as dirty when the user selects a different tab. However, you do not need to invalidate your window or its views for many content-related changes, unless the content changes themselves caused the window to be associated with a completely different set of data-providing objects. If you used the restorableStateKeyPaths method to declare the attributes you want to preserve, Cocoa preserves and restores the values of those attributes of your responder object. Therefore, any key paths you provide should be key-value observing compliant and generate the appropriate notifications. For more information on how to support key-value observing in your objects, see Key-Value Observing Programming Guide . Restoring Your Windows and Custom Objects at Launch TIme As part of your app’s normal launch cycle, Cocoa checks to see whether there is any preserved interface data. If there is, Cocoa usesthat data to try to re-create your app’s windows. Every window must identify a restoration class that knows about the window and can act on its behalf at launch time to create the window when asked to do so by Cocoa. The Core App Design Support the Key Runtime Behaviors in Your Apps 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 41The restoration class is responsible for creating both the window and all of the critical objects required by that window. For most app styles, the restoration class usually creates one or more controller objects as well. For example, in a single-window app, the restoration class would likely create the window controller used to manage the window and then retrieve the window from that object. Because it createsthese controller objects too, you typically use high-level application classesfor your restoration classes. An app might use the application delegate, a document controller, or even a window controller as a restoration class. During the launch cycle, Cocoa restores each preserved window as follows: 1. Cocoa retrieves the window’s restoration class from the preserved data and calls its restoreWindowWithIdentifier:state:completionHandler: class method. 2. The restoreWindowWithIdentifier:state:completionHandler: class method must call the provided completion handler with the desired window object. To do this, it does one of the following: ● It creates any relevant controller objects (including the window controller) that might normally be created to display the window. ● If the controller objects already exist (perhaps because they were already loaded from a nib file), the method gets the window from those existing objects. If the window could not be created, perhaps because the associated document was deleted by the user, the restoreWindowWithIdentifier:state:completionHandler: should pass an error object to the completion handler. 3. Cocoa uses the returned window to restore it and any preserved responder objects to their previous state. ● Standard Cocoa window and view objects are restored to their previousstate without additional help. If you subclass NSWindow or NSView, implement the restoreStateWithCoder: method to restore any custom state. If you implemented the restorableStateKeyPaths method in your custom responder objects, Cocoa automatically sets the value of the associated attributes to their preserved values. Thus, you do not have to implement the restoreStateWithCoder: to restore these attributes. ● For the window delegate object, Cocoa calls the window:didDecodeRestorableState: method to restore the state of that object. ● For your window controller, Cocoa calls the restoreStateWithCoder: method to restore its state. When re-creating each window, Cocoa passes the window’s unique identifier string to the restoration class. You are responsible for assigning user interface identifier strings to your windows prior to preserving the window state. You can assign an identifier in your window’s nib file or by setting your window object's identifier property (defined in NSUserInterfaceItemIdentification protocol). For example, you might give your preferences window an identifier of preferences and then check for that identifier in your The Core App Design Support the Key Runtime Behaviors in Your Apps 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 42implementation. Your restoration class can use this identifier to determine which window and associated objects it needs to re-create. The contents of an identifier string can be anything you want but should be something to help you identify the window later. For a single-window app whose main window controller and window are loaded from the main nib file, the job of your restoration class is fairly straightforward. Here, you could use the application delegate’s class as the restoration class and implement the restoreWindowWithIdentifier:state:completionHandler: method similar to the implementation shown in Listing 2-2. Because the app has only one window, it returns the main window directly. If you used the application delegate’s class asthe restoration classfor other windows, your own implementation could use the identifier parameter to determine which window to create. Listing 2-2 Returning the main window for a single-window app + (void)restoreWindowWithIdentifier:(NSString *)identifier state:(NSCoder *)state completionHandler:(void (^)(NSWindow *, NSError *))completionHandler { // Get the window from the window controller, // which is stored as an outlet by the delegate. // Both the app delegate and window controller are // created when the main nib file is loaded. MyAppDelegate* appDelegate = (MyAppDelegate*)[[NSApplication sharedApplication] delegate]; NSWindow* mainWindow = [appDelegate.windowController window]; // Pass the window to the provided completion handler. completionHandler(mainWindow, nil); } Apps Are Built Using Many Different Pieces The objects of the core architecture are important but are not the only objects you need to consider in your design. The core objects manage the high-level behavior of your app, but the objects in your app’s view layer do most of the work to display your custom content and respond to events. Other objects also play important roles in creating interesting and engaging apps. The Core App Design Apps Are Built Using Many Different Pieces 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 43The User Interface An app’s user interface is made up of a menu bar, one or more windows, and one or more views. The menu bar is a repository for commands that the user can perform in the app. Commands may apply to the app as a whole, to the currently active window, or to the currently selected object. You are responsible for defining the commands that your app supports and for providing the event-handling code to respond to them. You use windows and views to present your app’s visual content on the screen and to manage the immediate interactions with that content. A window is an instance of the NSWindow class. A panel is an instance of the NSPanel class(which is a descendant of NSWindow) that you use to presentsecondary content. Single-window apps have one main window and may have one or more secondary windows or panels. Multiwindow apps have multiple windows for displaying their primary content and may have one or more secondary windows or panels too. The style of a window determines its appearance on the screen. Figure 2-9 shows the menu bar, along with some standard windows and panels. Figure 2-9 Windows and menus in an app A view, an instance of the NSView class, defines the content for a rectangular region of a window. Views are the primary mechanism for presenting content and interacting with the user and have several responsibilities. For example: ● Drawing and animation support. Views draw content in their rectangular area. Views that support Core Animation layers can use those layers to animate their contents. ● Layout and subview management. Each view manages a list ofsubviews, allowing you to create arbitrary view hierarchies. Each view defineslayout and resizing behaviorsto accommodate changesin the window size. The Core App Design Apps Are Built Using Many Different Pieces 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 44● Event handling. Views receive events. Views forward events to other objects when appropriate. For information about creating and configuring windows, see Window Programming Guide . For information about using and creating view hierarchies, see View Programming Guide . Event Handling The system window server is responsible for tracking mouse, keyboard, and other events and delivering them to your app. When the system launches an app, it creates both a process and a single thread for the app. This initial thread becomes the app’s main thread. In it, the NSApplication object sets up the main run loop and configures its event-handling code, as shown in Figure 2-10. As the window server delivers events, the app queues those events and then processes them sequentially in the app’s main run loop. Processing an event involves dispatching the event to the object best suited to handle it. For example, mouse events are usually dispatched to the view in which the event occurred. Figure 2-10 Processing events in the main run loop Note: A run loop monitors sources of input on a specific thread of execution. The app’s event queue represents one of these inputsources. While the event queue is empty, the main thread sleeps. When an event arrives, the run loop wakes up the thread and dispatches control to the NSApplication object to handle the event. After the event has been handled, control passes back to the run loop, which can then process another event, process other input sources, or put the thread back to sleep if there is nothing more to do. For more information about how run loops and input sources work, see Threading Programming Guide . Distributing and handling events is the job of responder objects, which are instances of the NSResponder class. The NSApplication, NSWindow, NSDrawer, NSView, NSWindowController, and NSViewController classes are all descendants of NSResponder. After pulling an event from the event queue, the app dispatches The Core App Design Apps Are Built Using Many Different Pieces 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 45that event to the window object where it occurred. The window object, in turn, forwards the event to its first responder. In the case of mouse events, the first responder is typically the view object (NSView) in which the touch took place. For example, a mouse event occurring in a button is delivered to the corresponding button object. If the first responder is unable to handle an event, it forwardsthe event to its nextresponder, which istypically a parent view, view controller, or window. If that object is unable to handle the event, it forwards it to its next responder, and so , until the event is handled. Thisseries of linked responder objectsis known asthe responder chain. Messages continue traveling up the responder chain—toward higher-level responder objects, such as a window controller or the application object—until the event is handled. If the event isn't handled, it is discarded. The responder object that handles an event often sets in motion a series of programmatic actions by the app. For example, a control object (that is, a subclass of NSControl) handles an event by sending an action message to another object, typically the controller that manages the current set of active views. While processing the action message, the controller might change the user interface or adjust the position of views in ways that require some of those views to redraw themselves. When this happens, the view and graphics infrastructure takes over and processes the required redraw events in the most efficient manner possible. For more information about responders, the responder chain, and handling events, see Cocoa Event Handling Guide . Graphics, Drawing, and Printing There are two basic ways in which a Mac app can draw its content: ● Native drawing technologies (such as Core Graphics and AppKit) ● OpenGL The native OS X drawing technologies typically use the infrastructure provided by Cocoa views and windows to render and present custom content. When a view is first shown, the system asks it to draw its content. System views draw their contents automatically, but custom views must implement a drawRect: method. Inside this method, you use the native drawing technologies to draw shapes, text, images, gradients, or any other visual content you want. When you want to update your view’s visual content, you mark all or part of the view invalid by calling its setNeedsDisplay: or setNeedsDisplayInRect: method. The system then calls your view’s drawRect: method (at an appropriate time) to accommodate the update. This cycle then repeats and continues throughout the lifetime of your app. If you are using OpenGL to draw your app’s content, you still create a window and view to manage your content, but those objects simply provide the rendering surface for an OpenGL drawing context. Once you have that drawing context, your app is responsible for initiating drawing updates at appropriate intervals. The Core App Design Apps Are Built Using Many Different Pieces 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 46For information about how to draw custom content in your views, see Cocoa Drawing Guide . Text Handling The Cocoa text system, the primary text-handling system in OS X, is responsible for the processing and display of all visible text in Cocoa. It provides a complete set of high-quality typographical services through the text-related AppKit classes, which enable apps to create, edit, display, and store text with all the characteristics of fine typesetting. The Cocoa text system provides all these basic and advanced text-handling features, and it also satisfies additional requirements from the ever-more-interconnected computing world: support for the character sets of all of the world’s living languages, powerful layout capabilities to handle various text directionality and nonrectangular text containers, and sophisticated typesetting capabilities such as control of kerning, ligatures, line breaking, and justification. Cocoa’s object-oriented textsystem is designed to provide all these capabilities without requiring you to learn about or interact with more of the system than is necessary to meet the needs of your app. Underlying the Cocoa text system is Core Text, which provides low-level, basic text layout and font-handling capabilities to higher-level engines such as Cocoa and WebKit. Core Text provides the implementation for many Cocoa text technologies. App developers typically have no need to use Core Text directly. However, the Core Text API is accessible to developers who must use it directly, such as those writing apps with their own layout engine and those porting older ATSUI- or QuickDraw-based codebases to the modern world. For more information about the Cocoa text system, see Cocoa Text Architecture Guide . Implementing the Application Menu Bar The classes NSMenu and NSMenuItem are the basis for all types of menus. An instance of NSMenu manages a collection of menu items and draws them one beneath another. An instance of NSMenuItem represents a menu item; it encapsulates all the information its NSMenu object needs to draw and manage it, but does no drawing or event-handling itself. You typically use Interface Builder to create and modify any type of menu, so often there is no need to write any code. The application menu bar stretches across the top of the screen, replacing the menu bar of any other app when the app is foremost. All of an app’s menus in the menu bar are owned by one NSMenu instance that’s created by the app when it starts up. The Core App Design Implementing the Application Menu Bar 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 47Xcode Templates Provide the Menu Bar Xcode’s Cocoa application templates provide that NSMenu instance in a nib file called MainMenu.xib. This nib file contains an application menu (named with the app’s name), a File menu (with all of its associated commands), an Edit menu (with text editing commands and Undo and Redo menu items), and Format, View, Window, and Help menus (with their own menu items representing commands). These menu items, as well as all of the menu items of the File menu, are connected to the appropriate first-responder action methods. For example, the About menu item is connected to the orderFrontStandardAboutPanel: action method in the File’s Owner that displays a standard About window. The template has similar ready-made connections for the Edit, Format, View, Window, and Help menus. If your app does not support any of the supplied actions (for example, printing), you should remove the associated menu items (or menu) from the nib. Alternatively, you may want to repurpose and rename menu commands and action methodsto suit your own app, taking advantage of the menu mechanism in the template to ensure that everything is in the right place. Connect Menu Items to Your Code or Your First Responder For your app’s custom menu items that are not already connected to action methods in objects or placeholder objects in the nib file, there are two common techniques for handling menu commands in a Mac app: ● Connect the corresponding menu item to a first responder method. ● Connect the menu item to a method of your custom application object or your application delegate object. Of these two techniques, the first is more common given that many menu commands act on the current document or its contents, which are part of the responder chain. The second technique is used primarily to handle commands that are global to the app, such as displaying preferences or creating a new document. It is possible for a custom application object or its delegate to dispatch events to documents, but doing so is generally more cumbersome and prone to errors. In addition to implementing action methods to respond to your menu commands, you must also implement the methods of the NSMenuValidation protocol to enable the menu items for those commands. Step-by-step instructions for connecting menu items to action methods in your code are given in “Designing User Interfaces in Xcode”. For more information about menu validation and other menu topics, see Application Menu and Pop-up List Programming Topics. The Core App Design Implementing the Application Menu Bar 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 48Enabling a window of your app to assume full-screen mode, taking over the entire screen, provides users with a more immersive, cinematic experience. Full-screen appearance can be striking and can make your app stand out. From a practical standpoint, full-screen mode presents a better view of users’ data, enabling them to concentrate fully on their content without the distractions of other apps or the desktop. In full-screen mode, by default, the menu bar and Dock are autohidden; that is, they are normally hidden but reappear when the user moves the pointer to the top or bottom of the screen. A full-screen window does not draw its titlebar and may have special handling for its toolbar. The full-screen experience makes sense for many apps but not for all. For example, the Finder, Address Book, and Calculator would not provide any benefit to users by assuming full-screen mode. The same is probably true for most utility apps. Media-rich apps, on the other hand, can often benefit from full-screen presentation. Beginning with OS X v10.7, Cocoa includes support for full-screen mode through APIs in NSApplication, NSWindow, and NSWindowDelegate protocol. When the user chooses to enter full-screen mode, Cocoa dynamically creates a space and puts the window into that space. This behavior enables the user to have one window of an app running in full-screen mode in one space, while using other windows of that app, as well as other apps, on the desktop in otherspaces. While in full-screen mode, the user can switch between windows in the current app or switch apps. Apps that have implemented full-screen user interfaces in previous versions of OS X should consider standardizing on the full-screen APIs in OS X v10.7. Full-Screen API in NSApplication Full-screen support in NSApplication is provided by the presentation option NSApplicationPresentationFullScreen. You can find the current presentation mode via the NSApplication method currentSystemPresentationOptions, which is also key-value observable. You can set the presentation options using the NSApplication method setPresentationOptions:. (Be sure to observe the restrictions on presentation option combinations documented with NSApplicationPresentationOptions, and set the presentation optionsin a try-catch block to ensure that your program does not crash from an invalid combination of options.) 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 49 Implementing the Full-Screen ExperienceA window delegate may also specify that the window toolbar be removed from the window in full-screen mode and be shown automatically with the menu bar by including NSApplicationPresentationAutoHideToolbar in the presentation options returned from the window:willUseFullScreenPresentationOptions: method of NSWindowDelegate. Full-Screen API in NSWindow The app must specify whether a given window can enter full-screen mode. Apps can set collection behavior using the setCollectionBehavior: method by passing in various constants, and the current options may be accessed via the collectionBehavior method. You can choose between two constants to override the window collection behavior, as shown in the following table: Constant Behavior The frontmost window with this collection behavior becomes the full-screen window. A window with this collection behavior has a full-screen button in the upper right of its titlebar. NSWindowCollectionBehaviorFullScreenPrimary Windows with this collection behavior can be shown in the same space with the full-screen window. NSWindowCollectionBehaviorFullScreenAuxiliary When a window goesinto full-screen mode, the styleMask changesto NSFullScreenWindowMask to reflect the state of the window.The setting of the styleMask goesthrough the setStyleMask: method. As a result, a window can override this method if it has customization to do when entering or exiting full-screen. A window can be taken into or out of full-screen mode using the toggleFullScreen: method. If an app supports full-screen mode, it should add a menu item to the View menu with toggleFullScreen: as the action, and nil as the target. Full-Screen API in NSWindowDelegate Protocol The following notifications are sent before and after the window enters and exits full-screen mode: NSWindowWillEnterFullScreenNotification NSWindowDidEnterFullScreenNotification NSWindowWillExitFullScreenNotification NSWindowDidExitFullScreenNotification Implementing the Full-Screen Experience Full-Screen API in NSWindow 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 50The window delegate has the following corresponding window delegate notification methods: windowWillEnterFullScreen: windowDidEnterFullScreen: windowWillExitFullScreen: windowDidExitFullScreen: The NSWindowDelegate protocol methods supporting full-screen mode are listed in Table 3-1. Table 3-1 Window delegate methods supporting full-screen mode Method Description Invoked to allow the delegate to modify the full-screen content size. window: willUseFullScreenContentSize: Returns the presentation options the window will use when transitioning to full-screen mode. window: willUseFullScreenPresentationOptions: Invoked when the window is about to enter full-screen mode. The window delegate can implement this method to customize the animation by returning a custom window or array of windows containing layers or other effects. customWindowsToEnterFullScreenForWindow: The system has started its animation into full-screen mode, including transitioning into a new space. You can implement this method to perform custom animation with the given duration to be in sync with the system animation. window: startCustomAnimationToEnterFullScreenWithDuration: Invoked if the window failed to enter full-screen mode. windowDidFailToEnterFullScreen: Implementing the Full-Screen Experience Full-Screen API in NSWindowDelegate Protocol 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 51Method Description Invoked when the window is about to exit full-screen mode. The window delegate can implement this method to customize the animation when the window is about to exit full-screen by returning a custom window or array of windows containing layers or other effects. customWindowsToExitFullScreenForWindow: The system has started its animation out of full-screen, including transitioning back to the desktop space. You can implement this method to perform custom animation with the given duration to be in sync with the system animation. window: startCustomAnimationToExitFullScreenWithDuration: Invoked if the window failed to exit full-screen mode. windowDidFailToExitFullScreen: For more information about full-screen mode, see NSWindowDelegate Protocol Reference and the OS X Human Interface Guidelines. Implementing the Full-Screen Experience Full-Screen API in NSWindowDelegate Protocol 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 52During the design phase of creating your app, you need to think about how to implement certain features that users expect in well-formed Mac apps. Integrating these features into your app architecture can have an impact on the data model or may require cooperation between significantly different portions in the app. You Can Prevent the Automatic Relaunch of Your App By default, as part of the Resume feature of OS X v10.7, apps that were open at logout are relaunched by the system when the user logsin again. You can prevent the automatic relaunching of your app at login by sending it a disableRelaunchOnLogin message. This NSApplication method increments a counter that controls the app being relaunched; if the counter is 0 at the time the user logs out, then the app is relaunched when the user logs back in. The counter is initially zero, providing the default relaunch behavior. Your can reinstate automatic relaunching of your app by sending it an enableRelaunchOnLogin message. This message decrements the relaunch counter, so an equal number of disableRelaunchOnLogin and enableRelaunchOnLogin messages enables relaunching. Both methods are thread safe. If your app should not be relaunched because it launches via some other mechanism, such as the launchd system process, then the recommended practice is to send the app a disableRelaunchOnLogin message once, and never pair it with an enableRelaunchOnLogin message. If your app should not be relaunched because it triggers a restart (for example, if it is an installer), then the recommended practice is to send it a disableRelaunchOnLogin message immediately before you attempt to trigger a restart and send it an enableRelaunchOnLogin message immediately after. This procedure handles the case where the user cancels restarting; if the user later restarts for another reason, then your app should be relaunched. Making Your App Accessible Enables Many Users Millions of people have a disability or special need. These include visual and hearing impairments, physical disabilities, and cognitive and learning challenges. Access to computers is vitally important for this population, because computers can provide a level of independence that is difficult to attain any other way. As populations around the world age, an increasing number of people will experience age-related disabilities, such as vision or hearing loss. Current and future generations of the elderly will expect to be able to continue using their 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 53 Supporting Common App Behaviorscomputers and accessing their data, regardless of the state of their vision and hearing. Apps that support customizable text displays, access by a screen reader, or the replacement of visual cues by audible ones can serve this population well. OS X is designed to accommodate assistive technologies and has many built-in features to help people with disabilities. Users access most of this functionality through the Universal Access pane of System Preferences. Some of these built-in technologies take advantage of the same accessibility architecture that allows external assistive technologies to access your app. Designing your app with accessibility in mind not only allows you to reach a larger group of users, it results in a better experience for all your users. As a first step in designing your app, be sure to read OS X Human Interface Guidelines. That book provides detailed specifications and best practices for designing and implementing an intuitive, consistent, and aesthetically pleasing user interface that delivers the superlative experience Macintosh users have come to expect. During the design process, you also should be aware of the accessibility perspective on many basic design considerations. Consider the following basic accessibility-related design principles: ● Support full keyboard navigation. For many users, a mouse is difficult, if not impossible, to use. Consequently, a user should be able to perform all your app’s functions using the keyboard alone. ● Don’t override built-in keyboard shortcuts. This applies both to the keyboard shortcuts OS X reserves (listed in “Keyboard Shortcuts”) and to the accessibility-related keyboard shortcuts (listed in “Accessibility Keyboard Shortcuts”). As a general rule, you should never override reserved keyboard shortcuts. In particular, you should take care not to override accessibility-related keyboard shortcuts or your app will not be accessible to users who enable full keyboard access. A corollary to this principle is to avoid creating too many new keyboard shortcuts that are specific to your app. Users should not have to memorize a new set of keyboard commands for each app they use. ● Provide alternatives for drag-and-drop operations. If your app relies on drag-and-drop operations in its workflow, you should provide alternate ways to accomplish the same tasks. This may not be easy; in fact, it may require the design of an alternate interface for apps that are heavily dependent on drag and drop. ● Make sure there’s always a way out of your app’s workflow. This is important for all users, of course, but it’s essential for users of assistive technologies. A user relying on an assistive app to use your app may have a somewhat narrower view of your app’s user interface. For this reason, it’s especially important to make canceling operations and retracing steps easy. In addition to the basic design principles, you should consider the requirements of specific disabilities and resulting design solutions and adaptations you can implement. The main theme of these suggestions is to provide as many alternate modes of content display as possible, so that users can find the way that suits their needs best. Consider the following categories of disabilities: Supporting Common App Behaviors Making Your App Accessible Enables Many Users 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 54● Visual Disabilities. Visual disabilities include blindness, color blindness, and low vision. Make your app accessible to assistive apps, such as screen readers. Ensure that color is not the only source of come particular information in your user interface. Provide an audio option for all visual cues and feedback, as well as succinct descriptions of images and animated content. ● Hearing Disabilities. When you design the audio output of your app, remember that some users may not be able to hear your app’s sound effects well or at all. And, of course, there are situations in which any user could not use audio output effectively, such as in a library. Providing redundant audio and visual output can aid comprehension for users with other types of disabilities as well, such as cognitive and learning disabilities. ● Motor and Cognitive Disabilities. People with motor disabilities may need to use alternatives to the standard mouse and keyboard input devices. Other users may have difficulty with the fine motor control required to double-click a mouse or to press key combinations on the keyboard. Users with cognitive or learning disabilities may need extra time to complete tasks or respond to alerts. OS X providessupport for many types of disabilities at the system level through solutions offered in the Universal Access system preferences, illustrated in Figure 4-1. In addition, most standard Cocoa objects implement accessibility through the NSAccessibility protocol, providing reasonable default behavior in most cases, Cocoa apps built with standard objects are automatically accessible. In general, you need to explicitly implement the NSAccessibility protocol methods only if you subclass one of them, adding new behavior. Figure 4-1 Universal Access system preference dialog Supporting Common App Behaviors Making Your App Accessible Enables Many Users 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 55The NSAccessibility informal protocol defines methods that Cocoa classes must implement to make themselves available to an external assistive app. An assistive app interacts with your app to allow persons with disabilities to use your app. For example, a person with a visual impairment could use an app to convert menu items and button labels into speech and then perform actions by verbal command. An accessible object is described by a set of attributes that define characteristics such as the object type, its value, its size and position on the screen, and its place in the accessibility hierarchy. For some objects, the set of attributes can include parameterized attributes. Parameterized attributes behave similar to a function by allowing you to pass a parameter when requesting an attribute value. For more information, see Accessibility Overview for OS X . Provide User Preferences for Customization Preferences are settings that enable users to customize the appearance or behavior of your software. The OS X user defaultssystem lets you access and manage user preferences. You can use the defaultssystem to provide reasonable initial values for app settings, as well as save and retrieve the user's own preference selections across sessions. The Cocoa NSUserDefaults class provides programmatic access to the user defaults system. The NSUserDefaults class provides convenience methodsfor accessing common typessuch asfloats, doubles, integers, Booleans, and URLs. A default object must be a property list, that is, an instance of (or for collections a combination of instances of): NSData, NSString, NSNumber, NSDate, NSArray, or NSDictionary. If you want to store any other type of object, you should typically archive it to create an instance of NSData. The user defaults system groups defaults into domains. Two of the domains are persistently saved in the user defaults database: the app domain stores app-specific defaults, and the global domain stores defaults applicable to all apps. In addition, the user defaults system provides three volatile domains whose values last only while the user defaults object exists: the argument domain for defaults set from command-line arguments, the languages domain containing defaults for a locale if one is specified, and the registration domain for “factory defaults” registered by the app. Your app uses the NSUserDefaults class to register default preferences, and typically it also provides a user interface (a preferences panel) that enables the user to change those preferences. Preferences are stored in the ~/Library/Preferences/ folder in a standard XML-format property list file as a set of key-value pairs. The app-specific preferences property list is identified by the bundle identifier of the app. For more details, see Preferences and Settings Programming Guide . Supporting Common App Behaviors Provide User Preferences for Customization 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 56Integrate Your App With Spotlight Search Spotlight is a fast desktop search technology that allows users to organize and search for files based on metadata. Metadata is data about a file, rather than the actual content stored in the file. Metadata can include familiar information such as an asset’s author and modification date but it can also be keywords or other information that is custom to a particular asset. For example, an image file might have metadata describing the image’s dimensions and color model. Developers of appsthatsave documentsto disk should consider providing Spotlightsupport by implementing a metadata importer. A Spotlight metadata importer is a small plug-in bundle that you create to extract information from files created by your app. Spotlight importers are used by the Spotlight server to gather information about new and existing files, as illustrated in Figure 4-2. Figure 4-2 Spotlight extracting metadata Apple provides importers for many standard file types that the system uses, including RTF, JPEG, Mail, PDF and MP3. However, if you define a custom document format, you must create a metadata importer for your own content. Xcode provides a template for writing Spotlight importer plug-ins. For information about writing a Spotlight importer, see Spotlight Importer Programming Guide . In addition, you may wish to provide metadata search capability in your app. Cocoa provides the NSMetadataQuery class which enables you to construct queries using a subset of the NSPredicate classes and execute the queries asynchronously. For information about providing Spotlight search capability in your app, see File Metadata Search Programming Guide . For more information about Spotlight, see Spotlight Overview. Supporting Common App Behaviors Integrate Your App With Spotlight Search 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 57Use Services to Increase Your App’s Usefulness Services allow a user to access the functionality of one app from within another app. An app that provides a service advertises the operations it can perform on a particular type of data—for example, encryption of text, optical character recognition of a bitmapped image, or generating text such as a message of the day. When the user is manipulating that particular type of data in some app, the user can choose the appropriate item in the Services menu to operate on the current data selection (or merely insert new data into the document). See Services Implementation Guide for more information. Optimize for High Resolution High-resolution displays provide a rich visual experience, allowing users to see sharper text and more details in photos than on standard-resolution displays. The high-resolution model for OS X enables your app to draw into an abstract coordinate space called user space, without regard for the characteristics of the final drawing destination—printer, display screen, bitmap, or PDF—and without regard to the resolution of the display. OS X provides much support for high-resolution automatically. For example,standard AppKit views and controls automatically render correctly at any resolution, vector-based content automatically uses additional pixels to rendersharper lines and shapes, Cocoa text displayssharper in high-resolution, and AppKit automatically loads high-resolution variants of your images. You must do the following things to optimize your app for high-resolution: ● Provide properly-named high-resolution versions of your bitmapped images. ● Use high-resolution-savvy image-loading methods. ● Use the most recent APIs that support high resolution. These techniques are described in the following sections. Think About Points, Not Pixels OS X refers to screen size in points, not pixels. A point is one unit in user space, prior to any transformations on the space. Because, on a high-resolution display, there are four onscreen pixels for each point, points can be expressed asfloating-point values. Valuesthat are integersin standard resolution,such as mouse coordinates, are floating-point values on a high-resolution display, allowing for greater precision for such things as graphics alignment. Supporting Common App Behaviors Use Services to Increase Your App’s Usefulness 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 58Your app draws to a view using points in user space. The window server composites drawing operations to an offscreen buffer called the backing store. When it comes time to display the contents of the backing store onscreen, the window server scales the content appropriately, mapping points to onscreen pixels. The result is that if you draw the same content on two similar devices, and only one of them has a high-resolution screen, the content appears to be about the same size on both devices, as shown in Figure 4-3. Figure 4-3 Content appears the same size at standard resolution and high resolution In some situations you may need to know how points are mapped to pixels, in which case you can obtain the backing scale factor which is always either 1.0 or 2.0. The backing scale factor is a property of a layer, view, or window, and it depends on the resolution of the underlying display device. Provide High-Resolution Versions of Graphics OS X automatically magnifies standard-resolution bitmapped images so they appear to the user in the correct size, but they appear fuzzy. To avoid this problem, you must provide high-resolution versions of your graphics, along with the standard-resolution versions in the app bundle. In addition to any images your app displays, you must do this for your app’s icons and any custom controls, cursors, and other artwork. High-resolution graphics must be scaled with twice as many pixels in each dimension to display the same size in user space. For example, if you supply a standard-resolution image sized at 50x50 pixels, the high-resolution version must be sized at 100x100 pixels. For AppKit to recognize and load high-resolution versions of your graphics at appropriate times, you must adopt the naming convention of appending @2x to the image name. For example, a standard-resolution image named circle.png would have a high-resolution counterpart named circle@2x.png. Ideally, you can package both image versions into a single TIFF file. This is most easily done by setting the Xcode option Combine High Resolution Artwork to Yes in Target Build Settings under Deployment. Supporting Common App Behaviors Optimize for High Resolution 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 59You should create a set of icons for your app consisting of standard- and high-resolution versions of each icon size—16x16, 32x32, 128x128, 256x256, 512x512 appending @2x to the icon image name which, by convention, specifies the icon size in user space points. For example, an icon named icon_16x16.png would have a high-resolution counterpart named icon_16x16@2x.png, the icon_32x32.png size would have a version named icon_32x32@2x.png, and so on. After you’ve created your set of app icons, place them in folder a named icon.iconset. Then you can use the iconutil command-line tool to convert your .iconset folder into a single, deployment-ready, high-resolution .icns file. Use High-Resolution-Savvy Image-Loading Methods If you follow the @2x naming convention, there are two methods available that load standard- and high-resolution versions of an image into an NSImage object, whether or not you provide a multirepresentation image file: ● The NSImage method imageNamed: finds resources located in the main application bundle, but not in frameworks or plug-ins. ● The NSBundle method imageForResource: looks for resources outside as well as inside the main bundle. Framework authors should use this method. To create an NSImage object from a CGImageRef data type, use the initWithCGImage:size: method, specifying the image size in points, not pixels. For custom cursors, you can pass a multirepresentation TIFF to the NSCursor class method initWithImage:hotSpot:. Use APIs That Support High Resolution Cocoa apps must replace deprecated APIs with their newer counterparts. Apps that use older technologies need to replace those technologies with newer ones. NSImage, NSView, NSWindow, and NSScreen classes have methods that support high resolution, including methods for converting geometry, detecting scaling, and aligning pixels. These APIs and deprecated technologiesthat youmust avoid are described in High Resolution Guidelines for OS X . You should also consider whether your app requires further adjustments for special scenarios, such as using pixel-based technologies (OpenGL, Quartz bitmaps) or custom Core Animation layers. These advanced optimization techniques are described in High Resolution Guidelines for OS X , which also provides much more detailed information about high resolution. Supporting Common App Behaviors Optimize for High Resolution 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 60Prepare for Fast User Switching Fast user switching lets users share a single machine without having to log out every time they want to access their user account. Users share physical access to the machine, including the same keyboard, mouse, and monitor. However, instead of logging out, a new user simply logs in and switches out the previous user. Processes in a switched-out login session continue running as before. They can continue processing data, communicating with the system, and drawing to the screen buffer as before. However, because they are switched out, they do not receive input from the keyboard and mouse. Similarly, if they were to check, the monitor would appear to be in sleep mode. As a result, it may benefit some apps to adjust their behavior while in a switched-out state to avoid wasting system resources. While fast userswitching is a convenient feature for users, it does provide several challengesfor app developers. Apps that rely on exclusive access to certain resources may need to modify their behavior to live in a fast user switching environment. For example, an app that stores temporary data in /tmp may run into problems when a second instance running under a different user tries to modify the same files in that directory. To support fast user switching, there are certain guidelines you should follow in developing your apps, most of which describe safe waysto identify and share system resources. A summary of these guidelinesis asfollows: ● Incorporate session ID information into the name of any entity that appears in a global namespace, including file names, shared memory regions, semaphores, and named pipes. Tagging such app-specific resources with a session ID is necessary to distinguish them from similar resources created by apps in a different session. The Security layer of the system assigns a unique ID to each login session. Incorporating thisID into cache file or temporary directory names can prevent namespace collisions when creating these files. See “Supporting Fast User Switching” for information on how to get the session ID. ● Don't assume you have exclusive access to any resource, especially TCP/IP ports and hardware devices. ● Don't assume there is only one instance of a per-user service running. ● Use file-level or range-level locks when accessing files. ● Accept and handle user switch notifications. See “User Switch Notifications” for more information. For more information on user switching, see Multiple User Environment Programming Topics. Supporting Common App Behaviors Prepare for Fast User Switching 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 61Take Advantage of the Dock The Dock is a desktop app designed to reduce desktop clutter, provide users with feedback about an app, and allow users to switch easily between tasks. You can customize your app Dock tile by modifying the Dock icon and adding items to the menu displayed for your app, and you can customize the Dock icon of a minimized window. An app’s Dock icon is, by default, the app’s icon. While your app is running, you can modify or replace the default icon with another image that indicates the current state of your app. For example, the icon for Mail changes when messages are waiting to be read. A badge—the red circle and number in the figure—is overlaid onto Mail’s app icon to indicate the number of unread messages. The number changes each time Mail retrieves more messages. When the user holds the Control key down and clicks on a Dock tile, a menu appears. If your app does nothing to customize the menu, the Dock tile’s menu contains a list of the app’s open documents (if any), followed by the standard menu items Keep in Dock, Open at Login, Show in Finder, Hide, and Quit. You can add other menu itemsto the Dock menu, eitherstatically by providing a custom menu nib file, or dynamically by overriding the application delegate’s applicationDockMenu: method. You can also customize a dock tile when your app is not currently running by creating a Dock tile plug-in that can update the Dock tile icon and menu. For example, you may want to update the badge text to indicate that new content will be available the next time the app is launched, and you may want to customize the app’s Dock menu to deal with the new content. For information explaining how to customize your app’s Dock icon and menu, see Dock Tile Programming Guide . Supporting Common App Behaviors Take Advantage of the Dock 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 62Configuring your app properly is an important part of the development process. Mac apps use a structured directory configuration to manage their code and resource files. And although most of the files are custom and are there to support your app, some are required by the system or the App Store and must be configured properly. If you intend to sell your application through the Mac App Store or use iCloud storage, you also need to create an explicit app ID, create provisioning profiles, and enable the correct entitlements for your application. These procedures are explained in Tools Workflow Guide for Mac . All of the requirements for preparing your app and distributing it on the App Store are described in the App Store Resource Center. Configuring Your Xcode Project To develop a Mac app, you create an Xcode project. An Xcode Project is a repository for all the files, resources, and information required to build your app (or one of a number of othersoftware products). A project contains all the elements used to build your app and maintains the relationships between those elements. It contains one or more targets, which specify how to build the software. A project defines default build settings for all the targets in the project (each target can also specify its own build settings, which override the project build settings). You create a new project using the Xcode File > New > New Project menu command, which invokes the New Project dialog. This dialog enables you to choose a template for your project, such as a Cocoa app, to name it, and to locate it in your file system. The New Project dialog also provides options, so you can specify whether your app uses the Cocoa document architecture or the Core Data framework. When you save your project, Xcode lets you to create a local Git repository to enable source code control for your project. If you have two or more closely related projects, you should create an Xcode Workspace and add your projects to it. A workspace groups projects and other documents so you can work on them together. One project can use the products and shared libraries of another project while building, and Xcode does indexing across the entire workspace, extending the scope of content-aware features such as code completion. Once you have created your project, you write and edit your code using the Xcode source editor. You also use Xcode to build and debug your code, setting breakpoints, viewing the values of variables, stepping through running code, and reviewing issues found during builds or code analysis. 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 63 Build-Time Configuration DetailsWhen you create a new project, it includes one or more targets, where each target specifies one build product and the instructions for how the product is to be built. Most developers never need to change the default of the vast majority of build settings, but there are a few basic settings that you should check for each target, such as the deployment target (platform, OS version, and architecture), main user interface, and linked frameworks and libraries. You also need to set up one or more schemes to specify the targets, build configuration, and executable configuration to use when the product specified by the target is launched. You use the project editor and the scheme editing dialog to edit build settings and control what happens when you build and run your code. “Building and Running Your Code” explains how to work with Xcode build settings and schemes. For more information about using Xcode to create, configure, build, and debug your project, as well as archiving your program to package it for distribution or submission to the Mac App Store, see Xcode 4 User Guide . The Information Property List File An information property list (Info.plist) file contains essential runtime-configuration information for the app. Xcode provides a version of this file with every Mac application project and configures it with several standard keys. Although the default keys cover several important aspects of the app’s configuration, most apps require additional keys to specify their configuration fully. Build-Time Configuration Details The Information Property List File 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 64To view the contents of your Info.plist file, select it in the Groups & Files pane. Xcode displays a property list editor similar to the one in Figure 5-1 (which is from Xcode 3.2.5). You can use this window to edit the property values and add new key-value pairs. By default, Xcode displays a more user-friendly version of each key name. To see the key names that Xcode adds to the Info.plist file, Control-click an item in the editor and choose Show Raw Keys/Values from the contextual menu that appears. Figure 5-1 The information property list editor Xcode automatically addssome important keysto the Info.plist file of all new projects and setstheir initial values. However, there are several keys that Mac apps use commonly to configure their launch environment and runtime behavior. Here are some keysthat you might want to add to your app’s Info.plist file specifically for OS X: ● LSApplicationCategoryType (required for apps distributed using the App Store) ● CFBundleDisplayName ● LSHasLocalizedDisplayName ● NSHumanReadableCopyright ● LSMinimumSystemVersion ● UTExportedTypeDeclarations ● UTImportedTypeDeclarations Build-Time Configuration Details The Information Property List File 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 65For detailed information about these and other keys that you can include in your app’s Info.plist file, see Information Property List Key Reference . The OS X Application Bundle When you build your Mac app, Xcode packages it as a bundle. A bundle is a directory in the file system that groupsrelated resourcestogether in one place. A Mac app bundle contains a single Contents directory, inside of which are additional files and directories with the app’s code, resources, and localized content. Table 5-1 liststhe contents of a typical Mac app bundle, which for demonstration purposesis called MyApp. This example is for illustrative purposes only. Some of the files listed in this table may not appear in your own application bundles. Table 5-1 A typical application bundle Files Description The executable file containing your app’s code. The name of this file is the same as your app name minus the .app extension. This file is required. Contents/MacOS/MyApp Also known as the information property list file, a file containing configuration data for the app. The system uses this data to determine how to interact with the app at specific times. This file is required. For more information, see “The Information Property List File” (page 64). Contents/Info.plist Build-Time Configuration Details The OS X Application Bundle 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 66Files Description The English version of the app’s main nib file. This file contains the default interface objectsto load at app launch time. Typically, this nib file contains the app’s menu bar and application delegate object. It may also contain other controller objects that should always be available at launch time. (The name of the main nib file can be changed by assigning a different value to the NSMainNibFile key in the Info.plist file.) Thisfile is optional but recommended. For more information, see “The Information Property List File” (page 64) Contents/Resources/English.lproj/MainMenu.nib Nonlocalized resources are placed at the top level of the Resources directory (sun.png represents a nonlocalized image file in the example). The app uses nonlocalized resources when no localized version of the same resource is provided. Thus, you can use these files in situations where the resource is the same for all localizations. Contents/Resources/sun.png (or other resource files) Build-Time Configuration Details The OS X Application Bundle 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 67Files Description Localized resources are placed in subdirectories with an ISO 639-1 language abbreviation for a name plus an .lproj suffix. Although more human readable names (such as English.lproj, French.lproj, and German.lproj) can be used for directory names, the ISO 639-1 names are preferred because they allow you to include an ISO 3166-1 regional designation. (For example, the en_GB.lproj directory contains resources localized for English as spoken in Great Britain, the es.lproj directory contains resources localized for Spanish, and the de.lproj directory contains resources localized for German.) Contents/Resources/en_GB.lproj Contents/Resources/es.lproj Contents/Resources/de.lproj Other language-specific project directories A Mac app should be internationalized and have a language.lproj directory for each language it supports. Even if you provide localized versions of your resources, though, include a default version of these files at the top level of your Resources directory. The default version is used when a specific localization is not available. At runtime, you can access your app’s resource files from your code using the following steps: 1. Obtain a reference to your app’s main bundle object (typically using theNSBundle class). 2. Use the methods of the bundle object to obtain a file-system path to the desired resource file. 3. Open (or access) the file and use it. You obtain a reference to your app’s main bundle using the mainBundle class method of NSBundle. The pathForResource:ofType: method is one of several NSBundle methods that you can use to retrieve the location of resources. The following example shows how to locate a file called sun.png and create an image object using it. The first line getsthe bundle object and the path to the file. The second line creates an NSImage object that you could use to display the image in your app. NSString* imagePath = [[NSBundle mainBundle] pathForResource:@"sun" ofType:@"png"]; NSImage* sunImage = [[NSImage alloc] initWithContentsOfFile:imagePath]; Build-Time Configuration Details The OS X Application Bundle 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 68Note: If you prefer to use Core Foundation to access bundles, you can obtain a CFBundleRef opaque type using the CFBundleGetMainBundle function. You can then use that opaque type plus the Core Foundation functions to locate any bundle resources. For information on how to access and use resources in your app, see Resource Programming Guide . For more information about the structure of a Mac app bundle, see Bundle Programming Guide . Internationalizing Your App The process of preparing a project to handle content in different languages is called internationalization. The process of converting text, images, and other content into other languages is called localization. Project resources that are candidates for localization include: ● Code-generated text, including locale-specific aspects of date, time, and number formatting ● Static text—for example, strings you specify programmatically and display in parts of your user interface or an HTML file containing app help ● Icons (including your app icon) and other images when those images either contain text or have some culture-specific meaning ● Sound files containing spoken language ● Nib files Build-Time Configuration Details Internationalizing Your App 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 69Users select their preferred language from the Language and Text system preference, shown in Figure 5-2. Figure 5-2 The Language preference view Your application bundle can include multiple language-specific resource directories. The names of these directories consist of three components: an ISO 639-1 language code, an optional ISO 3166-1 region code, and a .lproj suffix. For example, to designate resourceslocalized to English, the bundle would be named en.lproj. By convention, these directories are called lproj directories. Note: You may use ISO 639-2 language codes instead of those defined by ISO 639-1. For more information about language and region codes, see “Language and Locale Designations” in Internationalization Programming Topics. Each lproj directory contains a localized copy of the app’s resource files. When you request the path to a resource file using the NSBundle class or the CFBundleRef opaque type, the path you get back automatically reflects the resource for the user’s preferred language. For more information about internationalization and how you support localized content in your Mac apps, see Internationalization Programming Topics. Build-Time Configuration Details Internationalizing Your App 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 70As you develop your app and your project code stabilizes, you can begin performance tuning. Of course, you want your app to launch and respond to the user’s commands as quickly as possible. A responsive app fits easily into the user’s workflow and feels well crafted. Speed Up Your App’s Launch Time You can improve your app’s performance at launch time by minimizing or deferring work until after the launch sequence has completed. The launch of an app provides users with the first impression of your app, and it’s something they see on a regular basis. Your overriding goal during launch should be to display the app’s menu bar and main window and then start responding to user commands as quickly as possible. Making your app responsive to commands quickly provides a better experience for the user. The following sections provide some general tips on how to make your app launch faster. Delay Initialization Code Many apps spend a lot of time initializing code that isn’t used until much later. Delaying the initialization of subsystems that are not immediately needed can speed up your launch time considerably. Remember that the goal is to display your app interface quickly, so try to initialize only the subsystems related to that goal initially. Once you have posted your interface, your app can continue to initialize additional subsystems as needed. However, remember that just because your app is able to process commands does not mean you need all of that code right away. The preferred way of initializing subsystems is on an as-needed basis. Wait until the user executes a command that requires a particular subsystem and then initialize it. That way, if the user never executes the command, you will not have wasted any time running the code to prepare for it. Avoid putting a lot of extraneous initialization code in your awakeFromNib methods. The system calls the awakeFromNib method of your main nib file before your app enters its main event loop. Use that method to initialize the objects in that nib and to prepare your app interface. For all other initialization, use the applicationDidFinishLaunching: method of your NSApplicationDelegate object instead. For more information on nib files and how they are loaded, see Resource Programming Guide . 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 71 Tuning for Performance and ResponsivenessSimplify Your Main Nib File Loading a nib file is an expensive process that can slow down your app launch time if you are not careful. When a nib file isloaded, all of the objectsin that file are instantiated and made ready for use. The more objects you include in your app’s main nib, the more time it takes to load that file and launch your app. The instantiation process for objects in a nib file requires that any frameworks used by those objects must themselves reside in memory. Thus loading a nib for a Cocoa app would likely require the loading of both the AppKit and Foundation frameworks, if they were not already resident in memory. Similarly, if you declare a custom class in your main nib file and that class relies on other frameworks, the system must load those frameworks as well. When designing your app’s main nib file, you should include only those objects needed to display your app’s initial user interface. Usually, this would involve just your app’s menu bar and initial window. For any custom classes you include in the nib, make sure their initialization code is as minimal as possible. Defer any time-consuming operations or memory allocations until after the class is instantiated. Minimize Global Variables For both apps and frameworks, be careful not to declare global variables that require significant amounts of initialization. The system initializes global variables before calling your app’s main routine. If you use a global variable to declare an object, the system must call the constructor or initialization method for that object during launch time. In general, it’s best to avoid declaring objects as global variables altogether when you can use a pointer instead. If you are implementing a framework or any type of reusable code module, you should also minimize the number of global variables you declare. Each app that links to a framework acquires a copy of that framework’s global variables. These variables might require several pages of virtual memory, which then increases the memory footprint of the app. An increased memory footprint can lead to paging in the app, which has a tremendous impact on performance. One way to minimize the global variables in a framework is to store the variables in a malloc-allocated block of memory instead. In this technique, you access the variables through a pointer to the memory, which you store as a global variable. Another advantage of this technique is that it allows you to defer the creation of any global variables until the first time they are actually used. See “Tips for Allocating Memory” in Memory Usage Performance Guidelines for more information. Tuning for Performance and Responsiveness Speed Up Your App’s Launch Time 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 72Minimize File Access at Launch Time Accessing a file is one of the slowest operations performed on a computer, so it is important that you do it as little as possible, especially at launch time. There is always some file access that must occur at launch time, such as loading your executable code and reading in your main nib file, but reducing your initial dependence on startup files can provide significant speed improvements. If you can delay the reading of a file until after launch time, do so. The following list includes some files whose contents you may not need until after launch: ● Frameworks not used directly by your app—Avoid calling code that uses nonessential frameworks until after launch. ● Nib files whose contents are not displayed immediately—Make sure your nib files and awakeFromNib: code are not doing too much at launch time. See “Simplify Your Main Nib File” (page 72) for more information. ● User preference files—User preferences may not be local so read them later if you can. ● Font files—Consider delaying font initialization until after the app has launched. ● Network files—Avoid reading files located on the network if at all possible. If you must read a file at launch time, do so only once. If you need multiple pieces of data from the same file, such as from a preferences file, consider reading all of the data once rather than accessing the file multiple times. Don’t Block the Main Thread The main thread is where your app handles user events and other input, so you should keep it free as much as possible to be responsive to the user. In particular, never use the main thread to perform long-running or potentially unbounded tasks, such as tasks that require network access. Instead, always move those tasks onto background threads. The preferred way to do so is to use Grand Central Dispatch (GCD) or operation objects to perform tasks asynchronously. For more information about doing work on background threads, see Concurrency Programming Guide . Decrease Your App’s Code Size In the context of performance, the more memory your app occupies, the more inefficient it is. More memory means more memory allocations, more code, and a greater potential for paging. Tuning for Performance and Responsiveness Don’t Block the Main Thread 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 73Reducing your code footprint is not just a matter of turning on code optimizations in your compiler, although that does help. You can also reduce your code footprint by organizing your code so that only the minimum set of required functions is in memory at any given time. You implement this optimization by profiling your code. See “Memory Instruments” in Instruments User Guide for information about profiling your app’s memory allocations. Compiler-Level Optimizations The Xcode compiler supports optimization options that let you choose whether you prefer a smaller binary size, faster code, or faster build times. For new projects, Xcode automatically disables optimizations for the debug build configuration and selects the Fastest, Smallest option for the release build configuration. Code optimizations of any kind result in slower build times because of the extra work involved in the optimization process. If your code is changing, as it does during the development cycle, you do not want optimizations enabled. As you near the end of your development cycle, though, the release build configuration can give you an indication of the size of your finished product, so the Fastest, Smallest option is appropriate. Table 6-1 lists the optimization levels available in Xcode. When you select one of these options, Xcode passes the appropriate flags to the compiler for the given group or files. These options are available at the target level or as part of a build configuration. See the Xcode Build System Guide for information on working with build settings for your project. Table 6-1 Compiler optimization options Xcode setting Description The compiler does not attempt to optimize code. Use this option during development when you are focused on solving logic errors and need a fast compile time. Do not use this option for shipping your executable. None The compiler performs simple optimizations to boost code performance while minimizing the impact to compile time. This option also uses more memory during compilation. Fast The compiler performs nearly all supported optimizations that do not require a space-time tradeoff. The compiler does not perform loop unrolling or function inlining with this option. This option increases both compilation time and the performance of generated code. Faster The compiler performs all optimizations in an attempt to improve the speed of the generated code. This option can increase the size of generated code as the compiler performs aggressive inlining of functions. This option is generally not recommended. Fastest Tuning for Performance and Responsiveness Decrease Your App’s Code Size 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 74Xcode setting Description The compiler performs all optimizations that do not typically increase code size. This is the preferred option for shipping code because it gives your executable a smaller memory footprint. Fastest, Smallest As with any performance enhancement, do not make assumptions about which option will give you the best results. You should always measure the results of each optimization you try. For example, the Fastest option might generate extremely fast code for a particular module, but it usually doesso at the expense of executable size. Any speed advantages you gain from the code generation are easily lost if the code needs to be paged in from disk at runtime. Use Core Data for Large Data Sets If your app manipulates large amounts of structured data, store it in a Core Data persistent store or in a SQLite database instead of in a flat file. Both Core Data and SQLite provide efficient ways to manage large data sets without requiring the entire set to be in memory all at once. Use SQLite if you deal with low-level data structures, or an existing SQLite database. Core Data provides a high-level abstraction for efficient object-graph management with an Objective-C interface; it is, however, an advanced framework and you shouldn't use it until you have gained adequate experience. For more information about Core Data, see Core Data Programming Guide and Optimizing Core Data with Instruments. Eliminate Memory Leaks Your app should not have any memory leaks. You can use the Instruments app to track down leaks in your code, both in the simulator and on actual devices. See “Memory Instruments” in Instruments User Guide for information about finding memory leaks. Dead Strip Your Code For statically linked executables, dead-code stripping is the process of removing unreferenced code from the executable file. If the code is unreferenced, it must not be used and therefore is not needed in the executable file. Removing dead code reduces the size of your executable and can help reduce paging. To enable dead-code stripping in Xcode, in the Linking group of Build Settings, set the Dead Code Stripping option to Yes. Tuning for Performance and Responsiveness Decrease Your App’s Code Size 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 75Strip Symbol Information Debugging symbols and dynamic-binding information can take up a lot of space and comprise a large percentage of your executable’s size. Before shipping your code, you should strip out all unneeded symbols. To strip debugging symbols from your executable, change the Xcode compiler code generation Generate Debug Symbols option to No. You can also generate debugging symbols on a target-by-target basis if you prefer. See the Xcode Help for more information on build configurations and target settings. Tuning for Performance and Responsiveness Decrease Your App’s Code Size 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 76This table describes the changes to Mac App Programming Guide . Date Notes Added a short section on adopting iCloud in a Mac app, “Integrating iCloud Support Into Your App” (page 30). 2012-07-23 Removed the chapter on iCloud, which is superseded by iCloud Design Guide . Rewrote section about supporting high resolution: “Optimize for High Resolution” (page 58). Summarized chapter on document-based apps, added iCloud chapter, and revised sandbox information. Made minor technical and editorial revisions throughout. Changed title from OS X Application Programming Guide. 2012-01-09 2011-06-27 New document describing the development process for Mac apps. 2012-07-23 | © 2012 Apple Inc. All Rights Reserved. 77 Document Revision HistoryApple Inc. © 2012 Apple Inc. All rights reserved. No part of this publication may be reproduced, stored in a retrievalsystem, or transmitted, in any form or by any means, mechanical, electronic, photocopying, recording, or otherwise, without prior written permission of Apple Inc., with the following exceptions: Any person is hereby authorized to store documentation on a single computer for personal use only and to print copies of documentation for personal use provided that the documentation contains Apple’s copyright notice. No licenses, express or implied, are granted with respect to any of the technology described in this document. Apple retains all intellectual property rights associated with the technology described in this document. This document is intended to assist application developers to develop applications only for Apple-labeled computers. Apple Inc. 1 Infinite Loop Cupertino, CA 95014 408-996-1010 Apple, the Apple logo, Bonjour, Cocoa, Finder, Instruments, iPhoto, iTunes, Keychain, Mac, Macintosh, Objective-C, OS X, Quartz, QuickDraw, Sand, Spotlight, Time Machine, and Xcode are trademarks of Apple Inc., registered in the U.S. and other countries. Launchpad is a trademark of Apple Inc. iCloud is a service mark of Apple Inc., registered in the U.S. and other countries. App Store and Mac App Store are service marks of Apple Inc. OpenGL is a registered trademark of Silicon Graphics, Inc. UNIX is a registered trademark of The Open Group. iOS is a trademark or registered trademark of Cisco in the U.S. and other countries and is used under license. Even though Apple has reviewed this document, APPLE MAKES NO WARRANTY OR REPRESENTATION, EITHER EXPRESS OR IMPLIED, WITH RESPECT TO THIS DOCUMENT, ITS QUALITY, ACCURACY, MERCHANTABILITY, OR FITNESS FOR A PARTICULAR PURPOSE.ASARESULT, THISDOCUMENT IS PROVIDED “AS IS,” AND YOU, THE READER, ARE ASSUMING THE ENTIRE RISK AS TO ITS QUALITY AND ACCURACY. IN NO EVENT WILL APPLE BE LIABLE FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL,OR CONSEQUENTIAL DAMAGES RESULTING FROM ANY DEFECT OR INACCURACY IN THIS DOCUMENT, even if advised of the possibility of such damages. THE WARRANTY AND REMEDIES SET FORTH ABOVE ARE EXCLUSIVE AND IN LIEU OF ALL OTHERS, ORAL OR WRITTEN, EXPRESS OR IMPLIED. No Apple dealer, agent, or employee is authorized to make any modification, extension, or addition to this warranty. Some states do not allow the exclusion or limitation of implied warranties or liability for incidental or consequential damages, so the above limitation or exclusion may not apply to you. This warranty gives you specific legal rights, and you may also have other rights which vary from state to state. Objective-C Runtime Programming GuideContents Introduction 5 Organization of This Document 5 See Also 5 Runtime Versions and Platforms 7 Legacy and Modern Versions 7 Platforms 7 Interacting with the Runtime 8 Objective-C Source Code 8 NSObject Methods 8 Runtime Functions 9 Messaging 10 The objc_msgSend Function 10 Using Hidden Arguments 13 Getting a Method Address 14 Dynamic Method Resolution 16 Dynamic Method Resolution 16 Dynamic Loading 17 Message Forwarding 18 Forwarding 18 Forwarding and Multiple Inheritance 20 Surrogate Objects 21 Forwarding and Inheritance 21 Type Encodings 24 Declared Properties 28 Property Type and Functions 28 Property Type String 29 Property Attribute Description Examples 30 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 2Document Revision History 33 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 3 ContentsFigures and Tables Messaging 10 Figure 3-1 Messaging Framework 12 Message Forwarding 18 Figure 5-1 Forwarding 20 Type Encodings 24 Table 6-1 Objective-C type encodings 24 Table 6-2 Objective-C method encodings 26 Declared Properties 28 Table 7-1 Declared property type encodings 30 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 4The Objective-C language defers as many decisions as it can from compile time and link time to runtime. Whenever possible, it does things dynamically. This means that the language requires not just a compiler, but also a runtime system to execute the compiled code. The runtime system acts as a kind of operating system for the Objective-C language; it’s what makes the language work. This document looks at the NSObject class and how Objective-C programs interact with the runtime system. In particular, it examines the paradigms for dynamically loading new classes at runtime, and forwarding messages to other objects. It also provides information about how you can find information about objects while your program is running. You should read this document to gain an understanding of how the Objective-C runtime system works and how you can take advantage of it. Typically, though, there should be little reason for you to need to know and understand this material to write a Cocoa application. Organization of This Document This document has the following chapters: ● “Runtime Versions and Platforms” (page 7) ● “Interacting with the Runtime” (page 8) ● “Messaging” (page 10) ● “Dynamic Method Resolution” (page 16) ● “Message Forwarding” (page 18) ● “Type Encodings” (page 24) ● “Declared Properties” (page 28) See Also Objective-C Runtime Reference describes the data structures and functions of the Objective-C runtime support library. Your programs can use these interfaces to interact with the Objective-C runtime system. For example, you can add classes or methods, or obtain a list of all class definitions for loaded classes. 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 5 IntroductionThe Objective-C Programming Language describes the Objective-C language. Objective-C Release Notes describes some of the changes in the Objective-C runtime in the latest release of OS X. Introduction See Also 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 6There are different versions of the Objective-C runtime on different platforms. Legacy and Modern Versions There are two versions of the Objective-C runtime—“modern” and “legacy”. The modern version wasintroduced with Objective-C 2.0 and includes a number of new features. The programming interface for the legacy version of the runtime is described in Objective-C 1 Runtime Reference ; the programming interface for the modern version of the runtime is described in Objective-C Runtime Reference . The most notable new feature is that instance variables in the modern runtime are “non-fragile”: ● In the legacy runtime, if you change the layout of instance variables in a class, you must recompile classes that inherit from it. ● In the modern runtime, if you change the layout of instance variables in a class, you do not have to recompile classes that inherit from it. In addition, the modern runtime supports instance variable synthesis for declared properties (see Declared Properties in The Objective-C Programming Language ). Platforms iPhone applications and 64-bit programs on OS X v10.5 and later use the modern version of the runtime. Other programs (32-bit programs on OS X desktop) use the legacy version of the runtime. 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 7 Runtime Versions and PlatformsObjective-C programs interact with the runtime system at three distinct levels: through Objective-C source code; through methods defined in the NSObject class of the Foundation framework; and through direct calls to runtime functions. Objective-C Source Code For the most part, the runtime system works automatically and behind the scenes. You use it just by writing and compiling Objective-C source code. When you compile code containing Objective-C classes and methods, the compiler creates the data structures and function calls that implement the dynamic characteristics of the language. The data structures capture information found in class and category definitions and in protocol declarations; they include the class and protocol objects discussed in Defining a Class and Protocols in The Objective-C Programming Language , as well as method selectors, instance variable templates, and other information distilled from source code. The principal runtime function is the one that sends messages, as described in “Messaging” (page 10). It’s invoked by source-code message expressions. NSObject Methods Most objects in Cocoa are subclasses of the NSObject class, so most objects inherit the methods it defines. (The notable exception is the NSProxy class; see “Message Forwarding” (page 18) for more information.) Its methods therefore establish behaviors that are inherent to every instance and every class object. However, in a few cases, the NSObject class merely defines a template for how something should be done; it doesn’t provide all the necessary code itself. For example, the NSObject class defines a description instance method that returns a string describing the contents of the class. This is primarily used for debugging—the GDB print-object command prints the string returned from this method. NSObject’s implementation of this method doesn’t know what the class contains,so it returns a string with the name and address of the object. Subclasses of NSObject can implement this method to return more details. For example, the Foundation class NSArray returns a list of descriptions of the objects it contains. 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 8 Interacting with the RuntimeSome of the NSObject methodssimply query the runtime system for information. These methods allow objects to perform introspection. Examples of such methods are the class method, which asks an object to identify its class; isKindOfClass: and isMemberOfClass:, which test an object’s position in the inheritance hierarchy; respondsToSelector:, which indicates whether an object can accept a particular message; conformsToProtocol:, which indicates whether an object claims to implement the methods defined in a specific protocol; and methodForSelector:, which provides the address of a method’s implementation. Methods like these give an object the ability to introspect about itself. Runtime Functions The runtime system is a dynamic shared library with a public interface consisting of a set of functions and data structuresin the header fileslocated within the directory /usr/include/objc. Many of these functions allow you to use plain C to replicate what the compiler does when you write Objective-C code. Others form the basis for functionality exported through the methods of the NSObject class. These functions make it possible to develop other interfacesto the runtime system and produce toolsthat augment the development environment; they’re not needed when programming in Objective-C. However, a few of the runtime functions might on occasion be useful when writing an Objective-C program. All of these functions are documented in Objective-C Runtime Reference . Interacting with the Runtime Runtime Functions 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 9This chapter describes how the message expressions are converted into objc_msgSend function calls, and how you can refer to methods by name. It then explains how you can take advantage of objc_msgSend, and how—if you need to—you can circumvent dynamic binding. The objc_msgSend Function In Objective-C, messages aren’t bound to method implementations until runtime. The compiler converts a message expression, [receiver message] into a call on a messaging function, objc_msgSend. This function takes the receiver and the name of the method mentioned in the message—that is, the method selector—as its two principal parameters: objc_msgSend(receiver, selector) Any arguments passed in the message are also handed to objc_msgSend: objc_msgSend(receiver, selector, arg1, arg2, ...) The messaging function does everything necessary for dynamic binding: ● It first finds the procedure (method implementation) that the selector refers to. Since the same method can be implemented differently by separate classes, the precise procedure that it finds depends on the class of the receiver. ● It then calls the procedure, passing it the receiving object (a pointer to its data), along with any arguments that were specified for the method. ● Finally, it passes on the return value of the procedure as its own return value. 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 10 MessagingNote: The compiler generates calls to the messaging function. You should never call it directly in the code you write. The key to messaging lies in the structures that the compiler builds for each class and object. Every class structure includes these two essential elements: ● A pointer to the superclass. ● A class dispatch table. This table has entries that associate method selectors with the class-specific addresses of the methods they identify. The selector for the setOrigin:: method is associated with the address of (the procedure that implements) setOrigin::, the selector for the display method is associated with display’s address, and so on. When a new object is created, memory for it is allocated, and its instance variables are initialized. First among the object’s variables is a pointer to its class structure. This pointer, called isa, gives the object access to its class and, through the class, to all the classes it inherits from. Messaging The objc_msgSend Function 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 11Note: While not strictly a part of the language, the isa pointer is required for an object to work with the Objective-C runtime system. An object needsto be “equivalent” to a struct objc_object (defined in objc/objc.h) in whatever fieldsthe structure defines. However, you rarely, if ever, need to create your own root object, and objects that inherit from NSObject or NSProxy automatically have the isa variable. These elements of class and object structure are illustrated in Figure 3-1. Figure 3-1 Messaging Framework . . . superclass selector...address selector...address selector...address . . . superclass selector...address selector...address selector...address . . . superclass selector...address selector...address selector...address isa instance variable instance variable . . . The object’s superclass The root class (NSObject) The object’s class Messaging The objc_msgSend Function 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 12When a message is sent to an object, the messaging function follows the object’s isa pointer to the class structure where it looks up the method selector in the dispatch table. If it can’t find the selector there, objc_msgSend followsthe pointer to the superclass and triesto find the selector in its dispatch table. Successive failures cause objc_msgSend to climb the class hierarchy until it reaches the NSObject class. Once it locates the selector, the function callsthe method entered in the table and passesit the receiving object’s data structure. This is the way that method implementations are chosen at runtime—or, in the jargon of object-oriented programming, that methods are dynamically bound to messages. To speed the messaging process, the runtime system caches the selectors and addresses of methods as they are used. There’s a separate cache for each class, and it can contain selectors for inherited methods as well as for methods defined in the class. Before searching the dispatch tables, the messaging routine first checks the cache of the receiving object’s class(on the theory that a method that was used once may likely be used again). If the method selector is in the cache, messaging is only slightly slower than a function call. Once a program has been running long enough to “warm up” its caches, almost all the messagesitsendsfind a cached method. Caches grow dynamically to accommodate new messages as the program runs. Using Hidden Arguments When objc_msgSend finds the procedure that implements a method, it calls the procedure and passes it all the arguments in the message. It also passes the procedure two hidden arguments: ● The receiving object ● The selector for the method These arguments give every method implementation explicit information about the two halves of the message expression that invoked it. They’re said to be “hidden” because they aren’t declared in the source code that defines the method. They’re inserted into the implementation when the code is compiled. Although these arguments aren’t explicitly declared, source code can still refer to them (just as it can refer to the receiving object’s instance variables). A method refers to the receiving object as self, and to its own selector as _cmd. In the example below, _cmd refers to the selector for the strange method and self to the object that receives a strange message. - strange { id target = getTheReceiver(); SEL method = getTheMethod(); Messaging Using Hidden Arguments 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 13if ( target == self || method == _cmd ) return nil; return [target performSelector:method]; } self is the more useful of the two arguments. It is, in fact, the way the receiving object’s instance variables are made available to the method definition. Getting a Method Address The only way to circumvent dynamic binding is to get the address of a method and call it directly as if it were a function. This might be appropriate on the rare occasions when a particular method will be performed many times in succession and you want to avoid the overhead of messaging each time the method is performed. With a method defined in the NSObject class, methodForSelector:, you can ask for a pointer to the procedure that implements a method, then use the pointer to call the procedure. The pointer that methodForSelector: returns must be carefully cast to the proper function type. Both return and argument types should be included in the cast. The example below shows how the procedure that implements the setFilled: method might be called: void (*setter)(id, SEL, BOOL); int i; setter = (void (*)(id, SEL, BOOL))[target methodForSelector:@selector(setFilled:)]; for ( i = 0; i < 1000, i++ ) setter(targetList[i], @selector(setFilled:), YES); The first two arguments passed to the procedure are the receiving object (self) and the method selector (_cmd). These arguments are hidden in method syntax but must be made explicit when the method is called as a function. Using methodForSelector: to circumvent dynamic binding saves most of the time required by messaging. However, the savings will be significant only where a particular message is repeated many times, as in the for loop shown above. Messaging Getting a Method Address 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 14Note that methodForSelector: is provided by the Cocoa runtime system; it’s not a feature of the Objective-C language itself. Messaging Getting a Method Address 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 15This chapter describes how you can provide an implementation of a method dynamically. Dynamic Method Resolution There are situations where you might want to provide an implementation of a method dynamically. For example, the Objective-C declared propertiesfeature (see Declared Properties in The Objective-C Programming Language ) includes the @dynamic directive: @dynamic propertyName; which tells the compiler that the methods associated with the property will be provided dynamically. You can implement the methods resolveInstanceMethod: and resolveClassMethod: to dynamically provide an implementation for a given selector for an instance and class method respectively. An Objective-C method is simply a C function that take at least two arguments—self and _cmd. You can add a function to a class as a method using the function class_addMethod. Therefore, given the following function: void dynamicMethodIMP(id self, SEL _cmd) { // implementation .... } you can dynamically add it to a class as a method (called resolveThisMethodDynamically) using resolveInstanceMethod: like this: @implementation MyClass + (BOOL)resolveInstanceMethod:(SEL)aSEL { if (aSEL == @selector(resolveThisMethodDynamically)) { class_addMethod([self class], aSEL, (IMP) dynamicMethodIMP, "v@:"); return YES; 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 16 Dynamic Method Resolution} return [super resolveInstanceMethod:aSEL]; } @end Forwarding methods (as described in “Message Forwarding” (page 18)) and dynamic method resolution are, largely, orthogonal. A class has the opportunity to dynamically resolve a method before the forwarding mechanism kicksin. If respondsToSelector: or instancesRespondToSelector: isinvoked, the dynamic method resolver is given the opportunity to provide an IMP for the selector first. If you implement resolveInstanceMethod: but want particular selectors to actually be forwarded via the forwarding mechanism, you return NO for those selectors. Dynamic Loading An Objective-C program can load and link new classes and categories while it’s running. The new code is incorporated into the program and treated identically to classes and categories loaded at the start. Dynamic loading can be used to do a lot of different things. For example, the various modules in the System Preferences application are dynamically loaded. In the Cocoa environment, dynamic loading is commonly used to allow applications to be customized. Others can write modules that your program loads at runtime—much as Interface Builder loads custom palettes and the OS X System Preferences application loads custom preference modules. The loadable modules extend what your application can do. They contribute to it in ways that you permit but could not have anticipated or defined yourself. You provide the framework, but others provide the code. Although there is a runtime function that performs dynamic loading of Objective-C modules in Mach-O files (objc_loadModules, defined in objc/objc-load.h), Cocoa’s NSBundle class provides a significantly more convenient interface for dynamic loading—one that’s object-oriented and integrated with related services. See the NSBundle classspecification in the Foundation framework reference for information on the NSBundle class and its use. See OS X ABI Mach-O File Format Reference for information on Mach-O files. Dynamic Method Resolution Dynamic Loading 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 17Sending a message to an object that does not handle that message is an error. However, before announcing the error, the runtime system gives the receiving object a second chance to handle the message. Forwarding If you send a message to an object that does not handle that message, before announcing an error the runtime sends the object a forwardInvocation: message with an NSInvocation object as its sole argument—the NSInvocation object encapsulates the original message and the arguments that were passed with it. You can implement a forwardInvocation: method to give a default response to the message, or to avoid the error in some other way. As its name implies, forwardInvocation: is commonly used to forward the message to another object. To see the scope and intent of forwarding, imagine the following scenarios: Suppose, first, that you’re designing an object that can respond to a message called negotiate, and you want itsresponse to include the response of another kind of object. You could accomplish this easily by passing a negotiate message to the other object somewhere in the body of the negotiate method you implement. Take this a step further, and suppose that you want your object’s response to a negotiate message to be exactly the response implemented in another class. One way to accomplish this would be to make your class inherit the method from the other class. However, it might not be possible to arrange things this way. There may be good reasons why your class and the class that implements negotiate are in different branches of the inheritance hierarchy. Even if your class can’t inherit the negotiate method, you can still “borrow” it by implementing a version of the method that simply passes the message on to an instance of the other class: - negotiate { if ( [someOtherObject respondsTo:@selector(negotiate)] ) return [someOtherObject negotiate]; return self; } 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 18 Message ForwardingThis way of doing things could get a little cumbersome, especially if there were a number of messages you wanted your object to pass on to the other object. You’d have to implement one method to cover each method you wanted to borrow from the other class. Moreover, it would be impossible to handle cases where you didn’t know, at the time you wrote the code, the full set of messages you might want to forward. That set might depend on events at runtime, and it might change as new methods and classes are implemented in the future. The second chance offered by a forwardInvocation: message provides a less ad hoc solution to this problem, and one that’s dynamic rather than static. It workslike this: When an object can’t respond to a message because it doesn’t have a method matching the selector in the message, the runtime system informsthe object by sending it a forwardInvocation: message. Every object inherits a forwardInvocation: method from the NSObject class. However, NSObject’s version of the method simply invokes doesNotRecognizeSelector:. By overriding NSObject’s version and implementing your own, you can take advantage of the opportunity that the forwardInvocation: message provides to forward messages to other objects. To forward a message, all a forwardInvocation: method needs to do is: ● Determine where the message should go, and ● Send it there with its original arguments. The message can be sent with the invokeWithTarget: method: - (void)forwardInvocation:(NSInvocation *)anInvocation { if ([someOtherObject respondsToSelector: [anInvocation selector]]) [anInvocation invokeWithTarget:someOtherObject]; else [super forwardInvocation:anInvocation]; } The return value of the message that’s forwarded is returned to the original sender. All types of return values can be delivered to the sender, including ids, structures, and double-precision floating-point numbers. A forwardInvocation: method can act as a distribution center for unrecognized messages, parceling them out to different receivers. Or it can be a transfer station, sending all messages to the same destination. It can translate one message into another, or simply “swallow” some messages so there’s no response and no error. A forwardInvocation: method can also consolidate several messages into a single response. What forwardInvocation: doesis up to the implementor. However, the opportunity it providesfor linking objects in a forwarding chain opens up possibilities for program design. Message Forwarding Forwarding 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 19Note: The forwardInvocation: method gets to handle messages only if they don’t invoke an existing method in the nominal receiver. If, for example, you want your object to forward negotiate messages to another object, it can’t have a negotiate method of its own. If it does, the message will never reach forwardInvocation:. For more information on forwarding and invocations, see the NSInvocation class specification in the Foundation framework reference. Forwarding and Multiple Inheritance Forwarding mimics inheritance, and can be used to lend some of the effects of multiple inheritance to Objective-C programs. As shown in Figure 5-1 (page 20), an object that responds to a message by forwarding it appears to borrow or “inherit” a method implementation defined in another class. Figure 5-1 Forwarding isa . . . – forwardInvocation: – negotiate negotiate isa . . . Warrior Diplomat In this illustration, an instance of the Warrior class forwards a negotiate message to an instance of the Diplomat class. The Warrior will appear to negotiate like a Diplomat. It will seem to respond to the negotiate message, and for all practical purposes it does respond (although it’s really a Diplomat that’s doing the work). The object that forwards a message thus“inherits” methodsfrom two branches of the inheritance hierarchy—its own branch and that of the object that responds to the message. In the example above, it appears as if the Warrior class inherits from Diplomat as well as its own superclass. Message Forwarding Forwarding and Multiple Inheritance 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 20Forwarding provides most of the features that you typically want from multiple inheritance. However, there’s an important difference between the two: Multiple inheritance combines different capabilities in a single object. It tends toward large, multifaceted objects. Forwarding, on the other hand, assigns separate responsibilitiesto disparate objects. It decomposes problemsinto smaller objects, but associatesthose objects in a way that’s transparent to the message sender. Surrogate Objects Forwarding not only mimics multiple inheritance, it also makes it possible to develop lightweight objects that represent or “cover” more substantial objects. The surrogate standsin for the other object and funnels messages to it. The proxy discussed in “Remote Messaging” in The Objective-C Programming Language is such a surrogate. A proxy takes care of the administrative details of forwarding messages to a remote receiver, making sure argument values are copied and retrieved across the connection, and so on. But it doesn’t attempt to do much else; it doesn’t duplicate the functionality of the remote object but simply gives the remote object a local address, a place where it can receive messages in another application. Other kinds of surrogate objects are also possible. Suppose, for example, that you have an object that manipulates a lot of data—perhaps it creates a complicated image or reads the contents of a file on disk. Setting this object up could be time-consuming, so you prefer to do it lazily—when it’s really needed or when system resources are temporarily idle. At the same time, you need at least a placeholder for this object in order for the other objects in the application to function properly. In this circumstance, you could initially create, not the full-fledged object, but a lightweight surrogate for it. This object could do some things on its own, such as answer questions about the data, but mostly it would just hold a place for the larger object and, when the time came, forward messages to it. When the surrogate’s forwardInvocation: method first receives a message destined for the other object, it would ensure that the object existed and would create it if it didn’t. All messages for the larger object go through the surrogate, so, as far as the rest of the program is concerned, the surrogate and the larger object would be the same. Forwarding and Inheritance Although forwarding mimics inheritance, the NSObject class never confuses the two. Methods like respondsToSelector: and isKindOfClass: look only at the inheritance hierarchy, never at the forwarding chain. If, for example, a Warrior object is asked whether it responds to a negotiate message, if ( [aWarrior respondsToSelector:@selector(negotiate)] ) ... Message Forwarding Surrogate Objects 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 21the answer is NO, even though it can receive negotiate messages without error and respond to them, in a sense, by forwarding them to a Diplomat. (See Figure 5-1 (page 20).) In many cases, NO is the right answer. But it may not be. If you use forwarding to set up a surrogate object or to extend the capabilities of a class, the forwarding mechanism should probably be astransparent asinheritance. If you want your objects to act as if they truly inherited the behavior of the objects they forward messages to, you’ll need to re-implement the respondsToSelector: and isKindOfClass: methods to include your forwarding algorithm: - (BOOL)respondsToSelector:(SEL)aSelector { if ( [super respondsToSelector:aSelector] ) return YES; else { /* Here, test whether the aSelector message can * * be forwarded to another object and whether that * * object can respond to it. Return YES if it can. */ } return NO; } In addition to respondsToSelector: and isKindOfClass:,the instancesRespondToSelector:method should also mirror the forwarding algorithm. If protocols are used, the conformsToProtocol: method should likewise be added to the list. Similarly, if an object forwards any remote messages it receives, it should have a version of methodSignatureForSelector: that can return accurate descriptions of the methods that ultimately respond to the forwarded messages; for example, if an object is able to forward a message to its surrogate, you would implement methodSignatureForSelector: as follows: - (NSMethodSignature*)methodSignatureForSelector:(SEL)selector { NSMethodSignature* signature = [super methodSignatureForSelector:selector]; if (!signature) { signature = [surrogate methodSignatureForSelector:selector]; } return signature; } Message Forwarding Forwarding and Inheritance 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 22You might consider putting the forwarding algorithm somewhere in private code and have all these methods, forwardInvocation: included, call it. Note: Thisis an advanced technique,suitable only forsituations where no othersolution is possible. It is not intended as a replacement for inheritance. If you must make use of this technique, make sure you fully understand the behavior of the class doing the forwarding and the class you’re forwarding to. The methods mentioned in this section are described in the NSObject class specification in the Foundation framework reference. For information on invokeWithTarget:, see the NSInvocation class specification in the Foundation framework reference. Message Forwarding Forwarding and Inheritance 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 23To assist the runtime system, the compiler encodes the return and argument types for each method in a character string and associates the string with the method selector. The coding scheme it uses is also useful in other contexts and so is made publicly available with the @encode() compiler directive. When given a type specification, @encode() returns a string encoding that type. The type can be a basic type such as an int, a pointer, a tagged structure or union, or a class name—any type, in fact, that can be used as an argument to the C sizeof() operator. char *buf1 = @encode(int **); char *buf2 = @encode(struct key); char *buf3 = @encode(Rectangle); The table below lists the type codes. Note that many of them overlap with the codes you use when encoding an object for purposes of archiving or distribution. However, there are codes listed here that you can’t use when writing a coder, and there are codesthat you may want to use when writing a coder that aren’t generated by @encode(). (See the NSCoder class specification in the Foundation Framework reference for more information on encoding objects for archiving or distribution.) Table 6-1 Objective-C type encodings Code Meaning c A char i An int s A short A long l is treated as a 32-bit quantity on 64-bit programs. l q A long long C An unsigned char I An unsigned int S An unsigned short 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 24 Type EncodingsCode Meaning L An unsigned long Q An unsigned long long f A float d A double B A C++ bool or a C99 _Bool v A void * A character string (char *) @ An object (whether statically typed or typed id) # A class object (Class) : A method selector (SEL) [array type ] An array {name=type...} A structure (name=type...) A union bnum A bit field of num bits ^type A pointer to type ? An unknown type (among other things, this code is used for function pointers) Important: Objective-C does not support the long double type. @encode(long double) returns d, which is the same encoding as for double. The type code for an array is enclosed within square brackets; the number of elements in the array is specified immediately after the open bracket, before the array type. For example, an array of 12 pointers to floats would be encoded as: [12^f] Structures are specified within braces, and unions within parentheses. The structure tag is listed first, followed by an equal sign and the codes for the fields of the structure listed in sequence. For example, the structure Type Encodings 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 25typedef struct example { id anObject; char *aString; int anInt; } Example; would be encoded like this: {example=@*i} The same encoding results whether the defined type name (Example) or the structure tag (example) is passed to @encode(). The encoding for a structure pointer carriesthe same amount of information about the structure’s fields: ^{example=@*i} However, another level of indirection removes the internal type specification: ^^{example} Objects are treated like structures. For example, passing the NSObject class name to @encode() yields this encoding: {NSObject=#} The NSObject class declares just one instance variable, isa, of type Class. Note that although the @encode() directive doesn’t return them, the runtime system uses the additional encodings listed in Table 6-2 for type qualifiers when they’re used to declare methods in a protocol. Table 6-2 Objective-C method encodings Code Meaning r const n in N inout Type Encodings 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 26Code Meaning o out O bycopy R byref V oneway Type Encodings 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 27When the compiler encounters property declarations (see Declared Properties in The Objective-C Programming Language ), it generates descriptive metadata that is associated with the enclosing class, category or protocol. You can accessthis metadata using functionsthatsupport looking up a property by name on a class or protocol, obtaining the type of a property as an @encode string, and copying a list of a property's attributes as an array of C strings. A list of declared properties is available for each class and protocol. Property Type and Functions The Property structure defines an opaque handle to a property descriptor. typedef struct objc_property *Property; You can use the functions class_copyPropertyList and protocol_copyPropertyList to retrieve an array of the properties associated with a class (including loaded categories) and a protocol respectively: objc_property_t *class_copyPropertyList(Class cls, unsigned int *outCount) objc_property_t *protocol_copyPropertyList(Protocol *proto, unsigned int *outCount) For example, given the following class declaration: @interface Lender : NSObject { float alone; } @property float alone; @end you can get the list of properties using: id LenderClass = objc_getClass("Lender"); unsigned int outCount; 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 28 Declared Propertiesobjc_property_t *properties = class_copyPropertyList(LenderClass, &outCount); You can use the property_getName function to discover the name of a property: const char *property_getName(objc_property_t property) You can use the functions class_getProperty and protocol_getProperty to get a reference to a property with a given name in a class and protocol respectively: objc_property_t class_getProperty(Class cls, const char *name) objc_property_t protocol_getProperty(Protocol *proto, const char *name, BOOL isRequiredProperty, BOOL isInstanceProperty) You can use the property_getAttributes function to discover the name and the @encode type string of a property. For details of the encoding type strings, see “Type Encodings” (page 24); for details of this string, see “Property Type String” (page 29) and “Property Attribute Description Examples” (page 30). const char *property_getAttributes(objc_property_t property) Putting these together, you can print a list of all the properties associated with a class using the following code: id LenderClass = objc_getClass("Lender"); unsigned int outCount, i; objc_property_t *properties = class_copyPropertyList(LenderClass, &outCount); for (i = 0; i < outCount; i++) { objc_property_t property = properties[i]; fprintf(stdout, "%s %s\n", property_getName(property), property_getAttributes(property)); } Property Type String You can use the property_getAttributes function to discover the name, the @encode type string of a property, and other attributes of the property. Declared Properties Property Type String 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 29The string starts with a T followed by the @encode type and a comma, and finishes with a V followed by the name of the backing instance variable. Between these, the attributes are specified by the following descriptors, separated by commas: Table 7-1 Declared property type encodings Code Meaning R The property is read-only (readonly). C The property is a copy of the value last assigned (copy). & The property is a reference to the value last assigned (retain). N The property is non-atomic (nonatomic). The property defines a custom getter selector name. The name follows the G (for example, GcustomGetter,). G The property defines a custom setter selector name. The name follows the S (for example, ScustomSetter:,). S D The property is dynamic (@dynamic). W The property is a weak reference (__weak). P The property is eligible for garbage collection. t Specifies the type using old-style encoding. For examples, see “Property Attribute Description Examples” (page 30). Property Attribute Description Examples Given these definitions: enum FooManChu { FOO, MAN, CHU }; struct YorkshireTeaStruct { int pot; char lady; }; typedef struct YorkshireTeaStruct YorkshireTeaStructType; union MoneyUnion { float alone; double down; }; Declared Properties Property Attribute Description Examples 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 30the following table shows sample property declarations and the corresponding string returned by property_getAttributes: Property declaration Property description @property char charDefault; Tc,VcharDefault @property double doubleDefault; Td,VdoubleDefault @property enum FooManChu enumDefault; Ti,VenumDefault @property float floatDefault; Tf,VfloatDefault @property int intDefault; Ti,VintDefault @property long longDefault; Tl,VlongDefault @property short shortDefault; Ts,VshortDefault @property signed signedDefault; Ti,VsignedDefault T{YorkshireTeaStruct="pot"i"lady"c},VstructDefault @property struct YorkshireTeaStruct structDefault; T{YorkshireTeaStruct="pot"i"lady"c},VtypedefDefault @property YorkshireTeaStructType typedefDefault; T(MoneyUnion="alone"f"down"d),VunionDefault @property union MoneyUnion unionDefault; @property unsigned unsignedDefault; TI,VunsignedDefault @property int (*functionPointerDefault)(char T^?,VfunctionPointerDefault *); @property id idDefault; T@,VidDefault Note: the compiler warns: no 'assign', 'retain', or 'copy' attribute is specified - 'assign' is assumed" @property int *intPointer; T^i,VintPointer @property void *voidPointerDefault; T^v,VvoidPointerDefault Declared Properties Property Attribute Description Examples 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 31Property declaration Property description @property int intSynthEquals; Ti,V_intSynthEquals In the implementation block: @synthesize intSynthEquals=_intSynthEquals; Ti,GintGetFoo,SintSetFoo: ,VintSetterGetter @property(getter=intGetFoo, setter=intSetFoo:) int intSetterGetter; @property(readonly) int intReadonly; Ti,R,VintReadonly @property(getter=isIntReadOnlyGetter, Ti,R,GisIntReadOnlyGetter readonly) int intReadonlyGetter; @property(readwrite) int intReadwrite; Ti,VintReadwrite @property(assign) int intAssign; Ti,VintAssign @property(retain)ididRetain; T@,&,VidRetain @property(copy)ididCopy; T@,C,VidCopy @property(nonatomic) int intNonatomic; Ti,VintNonatomic @property(nonatomic, readonly, copy) id T@,R,C,VidReadonlyCopyNonatomic idReadonlyCopyNonatomic; T@,R,&,VidReadonlyRetainNonatomic @property(nonatomic, readonly, retain) id idReadonlyRetainNonatomic; Declared Properties Property Attribute Description Examples 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 32This table describes the changes to Objective-C Runtime Programming Guide . Date Notes 2009-10-19 Made minor editorial changes. 2009-07-14 Completed list of types described by property_getAttributes. 2009-02-04 Corrected typographical errors. 2008-11-19 New document that describesthe Objective-C 2.0 runtime support library. 2009-10-19 | © 2009 Apple Inc. All Rights Reserved. 33 Document Revision HistoryApple Inc. © 2009 Apple Inc. All rights reserved. No part of this publication may be reproduced, stored in a retrievalsystem, or transmitted, in any form or by any means, mechanical, electronic, photocopying, recording, or otherwise, without prior written permission of Apple Inc., with the following exceptions: Any person is hereby authorized to store documentation on a single computer for personal use only and to print copies of documentation for personal use provided that the documentation contains Apple’s copyright notice. No licenses, express or implied, are granted with respect to any of the technology described in this document. Apple retains all intellectual property rights associated with the technology described in this document. This document is intended to assist application developers to develop applications only for Apple-labeled computers. Apple Inc. 1 Infinite Loop Cupertino, CA 95014 408-996-1010 Apple, the Apple logo, Cocoa, iPhone, Mac, Objective-C, and OS X are trademarks of Apple Inc., registered in the U.S. and other countries. Even though Apple has reviewed this document, APPLE MAKES NO WARRANTY OR REPRESENTATION, EITHER EXPRESS OR IMPLIED, WITH RESPECT TO THIS DOCUMENT, ITS QUALITY, ACCURACY, MERCHANTABILITY, OR FITNESS FOR A PARTICULAR PURPOSE.ASARESULT, THISDOCUMENT IS PROVIDED “AS IS,” AND YOU, THE READER, ARE ASSUMING THE ENTIRE RISK AS TO ITS QUALITY AND ACCURACY. 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Universal Binary Programming Guidelines, Second Edition (Legacy)Contents Introduction 8 Who Should Read This Document? 8 Organization of This Document 8 Assumptions 9 Conventions 10 Building a Universal Binary 11 Build Assumptions 11 Building Your Code 12 Debugging 16 Troubleshooting Your Built Application 16 Determining Whether a Binary Is Universal 18 Build Options 18 Default Compiler Options 19 Architecture-Specific Options 19 Autoconf Macros 20 See Also 20 Architectural Differences 21 Alignment 21 Bit Fields 21 Byte Order 21 Calling Conventions 22 Code on the Stack: Disabling Execution 22 Data Type Conversions 23 Data Types 23 Divide-By-Zero Operations 24 Extensible Firmware Interface (EFI) 24 Floating-Point Equality Comparisons 24 Structures and Unions 25 See Also 25 Swapping Bytes 26 Why Byte Ordering Matters 26 Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 2Guidelines for Swapping Bytes 28 Byte-Swapping Routines 29 Byte-Swapping Strategies 30 Constants 30 Custom Apple Event Data 31 Custom Resource Data 31 Floating-Point Values 32 Integers 33 Network-Related Data 34 OSType-to-String Conversions 35 Unicode Text Files 36 Values in an Array 38 Writing a Callback to Swap Data Bytes 38 See Also 45 Guidelines for Specific Scenarios 46 Aliases 46 Archived Bit Fields 46 Automator Scripts 46 Bit Shifting 47 Bit Test, Set, and Clear Functions: Carbon and POSIX 47 CPU Subtype 47 Dashboard Widgets 48 Deprecated Functions 48 Disk Partitions 48 Double-Precision Values: Bit-by-Bit Sensitivity 48 Finder Information and Low-Level File System Operations 49 FireWire Device Access 49 Font-Related Resources 50 GWorlds 50 Java Applications 51 Java I/O API (NIO) 51 Machine Location Data Structure 52 Mach Processes: The Task for PID Function 52 Metrowerks PowerPlant 53 Multithreading 53 Objective-C: Messages to nil 53 Objective-C Runtime: Sending Messages 54 Open Firmware 54 Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 3 ContentsOpenGL 55 OSAtomic Functions 58 Pixel Data 58 PostScript Printing 59 Quartz Bitmap Data 59 QuickDraw Routines 60 QuickTime Components 60 QuickTime Metadata Functions 61 Runtime Code Generation 61 Spotlight Importers 61 System-Specific Predefined Macros 62 USB Device Access 62 See Also 62 Preparing Vector-Based Code 63 Accelerate Framework 63 Rewriting AltiVec Instructions 64 See Also 64 Rosetta 65 What Can Be Translated? 65 How It Works 66 Special Considerations 66 Forcing an Application to Run Translated 68 Make a Setting in the Info Window 69 Use Terminal 69 Modify the Property List 69 Use the sysctlbyname Function 70 Preventing an Application from Opening Using Rosetta 71 Programmatically Detecting a Translated Application 71 Troubleshooting 73 Architecture-Independent Vector-Based Code 76 Architecture-Specific Code 76 Architecture-Independent Matrix Multiplication 82 32-Bit Application Binary Interface 84 64-Bit Application Binary Interface 85 Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 4 ContentsDocument Revision History 86 Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 5 ContentsFigures, Tables, and Listings Building a Universal Binary 11 Figure 1-1 The Build pane 14 Figure 1-2 Architectures settings 15 Figure 1-3 The Chess application has a Universal binary 18 Table 1-1 Default values for compiler flags on an Intel-based Macintosh computer 19 Architectural Differences 21 Listing 2-1 Code that illustrates byte-ordering differences 22 Listing 2-2 Architecture-dependent code 23 Listing 2-3 A union whose components can be affected by byte order 25 Swapping Bytes 26 Figure 3-1 Big-endian byte ordering compared to little-endian byte ordering 27 Table 3-1 Byte order marks 36 Listing 3-1 A data structure that contains multibyte and single-byte data 26 Listing 3-2 Encoding a 64-bit floating-point value 32 Listing 3-3 Decoding a 32-bit floating-point value 33 Listing 3-4 Swapping a 16-bit integer from big-endian to host-endian 34 Listing 3-5 Swapping integers from little-endian to host-endian 34 Listing 3-6 A routine for swapping the bytes of the values in an array 38 Listing 3-7 A declaration for a custom resource 40 Listing 3-8 A flipper function for RGBColor data 41 Listing 3-9 A flipper for the custom 'PREF' resource 41 Guidelines for Specific Scenarios 46 Figure 4-1 A test image that can help locate the source of color problems 58 Table 4-1 Quartz constants that specify byte ordering 59 Rosetta 65 Figure A-1 The Info window for the Calculator application 69 Figure A-2 Rosetta listens for a port connection 74 Figure A-3 Terminal windows with the commands for debugging a PowerPC binary on an Intel-based Macintosh computer 75 Listing A-1 A structure whose endian format depends on the architecture 67 Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 6Listing A-2 A routine that controls the preferred CPU type for sublaunched processes 70 Listing A-3 A utility routine for calling the sysctlbyname function 71 Listing A-4 A routine that determines whether a process is running natively or translated 72 Architecture-Independent Vector-Based Code 76 Listing B-1 Architecture-specific code needed to support matrix multiplication 77 Listing B-2 Architecture-independent code that performs matrix multiplication 82 Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 7 Figures, Tables, and ListingsUniversal Binary Programming Guidelines will assist experienced developers to build and modify their Mac OS X applications to run as universal binaries. Universal binaries run natively on Macintosh computers using PowerPC or Intel microprocessors and deliver optimal performance for both architectures in a single package. Important: This document may not represent best practices for current development. Links to downloads and other resources may no longer be valid. This document is designed to help developers determine exactly how much work needs to be done and provides useful tips for general as well as specific code modification scenarios. It describes the prerequisites for building code as a universal binary and shows how to do so using Xcode 2.2. It also discussesthe differences between the Intel and PowerPC architecturesthat can affect code behavior and provides guidelinesfor ensuring that universal binary code builds correctly. This version of Universal Binary Programming Guidelines represents a significant update since its introduction at the Apple Worldwide Developers Conference in June, 2005. It brings together all the information that developers need to make the transition to Intel-based Macintosh computers. This version includes pointers to newly revised tools documentation—“Building Universal Binaries” in Xcode Project Management Guide , GCC Porting Guide , Cross-Development Programming Guide , and more—as well as improved guidelines and tips. Anyone who has an older version of Universal Binary Programming Guidelines will want to replace it with this version. Who Should Read This Document? Any developer who currently has an application that runs in Mac OS X will want to read this document to learn how to modify their code so that it runs natively on all current Apple hardware. Developers who have not yet written an application for the Macintosh, but are planning to do so, will want to follow the guidelines in the document to ensure that their code can run as a universal binary. Organization of This Document This document is organized into the following chapters: Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 8 Introduction● “Building a Universal Binary” (page 11) shows how to use Xcode 2.2 to build native and universal binaries, describes build options, and provides troubleshooting information for code that doesn’t run properly on an Intel-based Macintosh computer. ● “Architectural Differences” (page 21) outlines the major differences between the x86 and PowerPC architectures. Understanding the differences will help you to write portable code. ● “Swapping Bytes” (page 26) describes byte-ordering differences in detail, provides a list of byte-swapping routines, and discusses strategies for a number of scenarios that require you to swap bytes. This is a must-read chapter for all Mac OS X developers. It will help you understand how to avoid byte-ordering issues when transferring data and data files between architectures. ● “Guidelines for Specific Scenarios” (page 46) contains tips for a variety of situations that are not common to most applications. ● “Preparing Vector-Based Code” (page 63) discusses the options available for those developers who have high-performance computing needs. This document contains the following appendixes: ● “Rosetta” (page 65) describesthe translation processthat allows PowerPC binariesto run on an Intel-based Macintosh computer. ● “Architecture-Independent Vector-Based Code” (page 76) uses matrix multiplication as an example to show how to write vector code with a minimum amount of architecture-specific coding. ● “32-Bit Application Binary Interface” (page 84) provides information on where to find details. ● “64-Bit Application Binary Interface” (page 85) provides information on where to find details. Assumptions The document assumes the following: ● Your application runs in Mac OS X. Your application can use any of the Mac OS X development environments: Carbon, Cocoa, Java, or BSD UNIX. If your application runs in the UNIX operating system but not specifically in Mac OS X, you should first read Porting UNIX/Linux Applications to Mac OS X . If your application runs only in the Windows operating system, you should first read Porting to Mac OS X from Windows Win32 API . If you are new to Mac OS X, you should take a look at Mac OS X Technology Overview. ● You know how to use Xcode. Introduction Assumptions Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 9Currently Xcode is the only GUI tool available that compiles code to run universally. If you are unfamiliar with Xcode, you might want to take a look at Xcode Workspace Guide . If you have been using CodeWarrior, you should read Porting CodeWarrior Projects to Xcode . Conventions The term x86 is a generic term used in some parts of this book to refer to the class of microprocessors manufactured by Intel. This book uses the term x86 as a synonym for IA-32 (Intel Architecture 32-bit). Introduction Conventions Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 10Architectural differences between Macintosh computersthat use Intel and PowerPC microprocessors can cause existing PowerPC code to behave differently when built and run natively on a Macintosh computer that uses an Intel microprocessor. The extent to which architectural differences affect your code depends on the level of your source code. Most existing code is high-level source code that is not specific to the processor. If your application falls into this category, you’ll find that creating a universal binary involves adjusting code in a few places. Cocoa developers may need to make fewer adjustments than Carbon developers whose code was ported from Mac OS 9 to Mac OS X. Most code that uses high-level frameworks and that builds with GCC 4.0 in Mac OS X v10.4 will build with few, if any, changes on an Intel-based Macintosh computer. The best approach for any developer in that situation isto build the existing code as a universal binary, as described in this chapter, and then see how the application runs on an Intel-based Macintosh. Find the places where the code doesn’t behave as expected and consult the sections in this document that cover those issues. Developers who use AltiVec instructions in their code or who intentionally exploit architectural differences for optimization or other purposes will need to make the most code adjustments. These developers will probably want to consult the rest of this document before building a universal binary. AltiVec programmers should read “Preparing Vector-Based Code” (page 63). This chapter describes how to use Xcode 2.2 to create a universal binary, providestroubleshooting information, and listsrelevant build options. You’ll find that the software development workflow on an Intel-based Macintosh computer is exactly the same as the software development workflow on a PowerPC-based Macintosh. Build Assumptions Before you build your code as a universal binary, you must ensure that: ● Your application already builds for Mac OS X. Your application can use any of the Mac OS X development environments: Carbon, Cocoa, Java, or BSD UNIX. ● Your application uses the Mach-O executable format. Mach-O binaries are the only type of binary that run natively on an Intel-based Macintosh computer. If you are already using the Xcode compilers and linkers, your application is a Mach–O binary. Carbon applications based on the Code Fragment Manager Preferred Executable Format (PEF) must be changed to Mach-O. Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 11 Building a Universal Binary● Your Xcode target is a native Xcode target. If it isn’t, in Xcode you can choose Project > Upgrade All Targets in Project to Native. ● Your code project is ported to GCC 4.0. Xcode uses GCC 4.0 for targeting Intel-based Macintosh computers. You may want to look at the document GCC Porting Guide to assess whether you need to make any changes to your code to allow it to compile using GCC 4.0. ● You installed the Mac OS X v10.4 universal SDK. The installer places the SDK in this location: /Developer/SDKs/MacOSX10.4u.sdk Building Your Code If you have already been using Xcode to build applications on a PowerPC-based Macintosh, you’ll see that building your code on an Intel-based Macintosh computer is accomplished in the same way. By default, Xcode compiles code to run on the architecture on which you build your Xcode project. Note that your Xcode target must be a native target. Tip: CodeWarrior users can read Xcode From a CodeWarrior Perspective for a discussion of the similarities and differences between the two. Thisinformation can help you to put your CodeWarrior experience to work in Xcode. When you are in the process of developing your project, you’ll want to use the following settingsfor the Default and Debug configurations: ● Keep the Architectures settings set to $(NATIVE_ARCH). ● Change the Mac OS X Deployment Target settings to Mac OS X 10.4. ● Make sure the SDKROOT setting is /Developer/SDKs/MacOSX10.4u.sdk. You can set the SDK root for the project by following these steps: 1. Open your project in Xcode 2.2 or later. Make sure that your Xcode target is a native target. If it isn’t, you can choose Project > Upgrade All Targets in Project to Native. 2. In the Groups & Files list, click the project name. 3. Click the Info button to open the Info window. 4. In the General pane, in the Cross-Develop Using Target SDK pop-up menu, choose Mac OS X 10.4 (Universal). Building a Universal Binary Building Your Code Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 12If you don’t see Mac OS X 10.4 (Universal) as a choice, look in the following directory to make sure that the universal SDK is installed: /Developer/SDKs/MacOSX10.4u.sdk If it’s not there, you’ll need to install this SDK before you can continue. 5. Click Change in the sheet that appears. The Debug build configuration turns on ZeroLink, Fix and Continue, and debug-symbol generation, among other settings, and turns off code optimization. When you are ready to test your application on both architectures, you’ll want to use the Release configuration. This configuration turns off ZeroLink and Fix and Continue. It also sets the code-optimization level to optimize for size. As with the Default and Debug configurations, you’ll want to set the Mac OS X Deployment Target to Mac OS X 10.4 and the SDK root to MacOSX10.4u.sdk. To build a universal binary, the Architecturessetting for the Release configuration must be set to build on Intel and PowerPC. You can change the Architectures setting by following these steps: 1. Open your project in Xcode 2.2 or later. 2. In the Groups & Files list, click the project name. 3. Click the Info button to open the Info window. Building a Universal Binary Building Your Code Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 134. In the Build pane (see Figure 1-1), choose Release from the Configuration pop-up menu. Figure 1-1 The Build pane Building a Universal Binary Building Your Code Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 145. Select the Architectures setting and click Edit. In the sheet that appears, select the PowerPC and Intel options, as shown in Figure 1-2. Figure 1-2 Architectures settings 6. Close the Info window. 7. Build and run the project. If your application doesn’t build, see “Debugging” (page 16). If your application builds but does not behave as expected when you run it as a native binary on an Intel-based Macintosh computer, see “Troubleshooting Your Built Application” (page 16). If your application behaves as expected, don’t assume that it also works on the other architecture. You need to test your application on both PowerPC Macintosh computers and Intel-based Macintosh computers. If your application reads data from and writes data to disk, you should make sure that you can save files on one architecture and open them on the other. Building a Universal Binary Building Your Code Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 15Note: Xcode 2.x has per-architecture SDK support. For example, you can target Mac OS X versions 10.3 and 10.4 for PowerPC while also targeting Mac OS X v10.4 and later for Intel-based Macintosh computers. For information on default compiler settings, architecture-specific options, and Autoconf macros, see “Build Options” (page 18). For information on building with version-specific SDKs for PowerPC (Mac OS X v10.3, v10.2, and so forth) while still building a universal binary for both PowerPC and Intel-based Macintosh computers, see the following resources: ● Using Cross Development in Xcode. ● Cross-Development and Universal Binaries in the Cross-Development Programming Guide provides details on to create executable files that contain object code for both Intel-based and PowerPC-based Macintosh computers. Debugging Xcode uses GDB for debugging,so you’ll wantto review the XcodeDebuggingGuide document. Xcode provides a powerful user interface to GDB that lets you step through your code, set breakpoints and view variables, stack frames, and threads. Debugging with GDB—an Open Source document that explains how to use GDB—is another useful resource that you’ll want to look at. It provides a lot of valuable information, including how to get a list of breakpoints for debugging. If you are moving code to GCC 4.0, you can find remedies for most linking issues and compiler warnings by consulting GCC Porting Guide . You can find additional information on the GCC options you can use to request or suppress warnings in Section 3.8 of the GNU C/C++/Objective-C 4.0.1 Compiler User Guide . Troubleshooting Your Built Application Here are the most typical behavior problems you’ll observe when your application runs natively on an Intel-based Macintosh computer: ● The application crashes. ● There are unexpected numerical results. Building a Universal Binary Debugging Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 16● Color is displayed incorrectly. ● Text is not displayed properly—characters from the Last Resort font or unexpected Chinese or Japanese characters appear. ● Files are not read or written correctly. ● Network communication does not work properly. The first two problems in the list are typically caused by architecture-dependent code. On an Intel-based Macintosh computer, an integer divide-by-zero exception resultsin a crash, but on PowerPC the same operation returns zero. In these cases, the code must be rewritten in an architecture-independent manner. “Architectural Differences” (page 21) discusses the major differences between Macintosh computers that use PowerPC and Intel microprocessors. That chapter can help you determine which code is causing the crash or the unexpected numerical results. The last four problems in the list are most often caused by byte-ordering differences between architectures. These problems are easily remedied by taking the byte order into account when you read and write data. The strategies available for handling byte ordering, as well as an in-depth discussion of byte-ordering differences, are provided in “Swapping Bytes” (page 26). Keep in mind that Mac OS X ensures that byte-ordering is correct for anything it is responsible for. Apple-defined resources (such as menus) won’t result in problem behavior. Custom resources provided by your application, however, can result in problem behavior. For example, if images in your application seem to have a cyan tint, it’s quite likely that your application is writing alpha channel data to the blue channel. For this specific issue, depending on the APIs that you are using, you’d want to consult the sections “GWorlds” (page 50), “Pixel Data ” (page 58), or other graphics-related sections in “Guidelines for Specific Scenarios” (page 46). Apple engineers prepared a lot of code to run natively on an Intel-based Macintosh computer—including the operating system, most Apple applications, and Apple tools. The guidelines in this book are the result of their work. In addition to the more common issues discussed in “Architectural Differences” (page 21) and “Swapping Bytes” (page 26), the engineers identified a number of narrowly focused issues. These are described in “Guidelines for Specific Scenarios” (page 46). You will want to at least glance at this chapter to see if your code can benefit from any of the information. Building a Universal Binary Troubleshooting Your Built Application Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 17Determining Whether a Binary Is Universal You can determine whether an application has a universal binary by looking at the Kind entry in the General section of the Info window for the application (see Figure 1-3). To open the Info window, click the application icon and press Cmd-I. Figure 1-3 The Chess application has a Universal binary On an Intel-based Macintosh computer, when you double-click an application that doesn’t have an executable for the native architecture, it might launch. Whether or not it launches depends on how compatible the application is with Rosetta. For more information, see “Rosetta” (page 65). Build Options This section contains information on the build options that you need to be aware of when using Xcode 2.2 and later on an Intel-based Macintosh computer. It lists the default compiler options, discusses how to set architecture-specific options, and provides information on using GNU Autoconf macros. Building a Universal Binary Determining Whether a Binary Is Universal Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 18Default Compiler Options In Xcode 2.2 and later on an Intel-based Macintosh computer, the defaults for compiler flags that differ from standard GCC distributions are listed in Table 1-1. Table 1-1 Default values for compiler flags on an Intel-based Macintosh computer Compiler flag Default value Specifies to -mfpmath sse Use SSE instructions for floating-point math. Enable the MMX, SSE, and SSE2 extensions in the Intel instruction set architecture. -msse2 On by default Architecture-Specific Options Most developers don’t need to use architecture-specific options for their projects. In Xcode, to set one flag for an Intel-based Macintosh and another for PowerPC, you use the PER_ARCH_CFLAGS_i386 and PER_ARCH_CFLAGS_ppc build settings variables to supply the architecture-specific settings. For example to set the architecture-specific flags -faltivec and -msse3, you would add the following build settings: PER_ARCH_CFLAGS_i386 = -msse3 PER_ARCH_CFLAGS_ppc = -faltivec Similarly, you can supply architecture-specific linker flags using the OTHER_LDFLAGS_i386 and OTHER_LDFLAGS_ppc build settings variables. You can pass the -arch flag to gcc, ld, and as. The allowable values are i386 and ppc. You can specify both flags as follows: -arch ppc -arch i386 Formore information on architecture-specific options,see“BuildingUniversal Binaries”in Xcode Project Management Guide . Building a Universal Binary Build Options Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 19Autoconf Macros If you are compiling a project that uses GNU Autoconf and trying to build it for both PowerPC-based and Intel-based Macintosh computers, you need to make sure that when the project configures itself, it doesn't use Autoconf macros to determine the endian type of the runtime system. For example, if your project uses the Autoconf AC_C_BIGENDIAN macro, the program won't work correctly when it is run on the opposite architecture from the one you are targeting when you configure the project. To correctly build for both PowerPC-based and Intel-based Macintosh computers, use the compiler-defined __BIG_ENDIAN__ and __LITTLE_ENDIAN__ macros in your code. For more information, see Using GNU Autoconf in Porting UNIX/Linux Applications to Mac OS X . See Also These resources provide information related to compiling and building applications, andmeasuring performance: ● Xcode Project Management Guide contains all the instructions needed to compile and debug any type of Xcode project (C, C++, Objective C, Java, AppleScript, resource, nib files, and so forth). ● GCC Porting Guide provides advice for how to modify your code in ways that make it more compatible with GCC 4.0. ● GNU C/C++/Objective-C 4.0.1 Compiler User Guide provides details about the GCC implementation. Xcode uses the GNU compiler collection (GCC) to compile code. The assembler (as) used by Xcode supports AT&T System V/386 assembler syntax in order to maintain compatibility with the output from GCC. The AT&T syntax is quite different from Intel syntax. The major differences are discussed in the GNU documentation. ● C++ Runtime Environment Programming Guide provides information on the GCC 4.0 shared C++ runtime that is available in Panther 10.3.9 and later. ● Porting UNIX/Linux Applications to Mac OS X . Developers porting from UNIX and Linux applications who want to compile a universal binary, will want to read the section Compiling for Multiple Architectures. ● Kernel Extension Programming Topics containsinformationaboutdebuggingKEXTsonIntel-basedMacintosh computers. ● Performance tools. Shark, MallocDebug, ObjectAlloc, Sampler, Quartz Debug, Thread Viewer, and other Apple-developed tools (some command-line, others use a GUI) are in the /Developer directory. Command-line performance tools are in the /usr/bin directory. ● Code Size Performance Guidelines and Code Speed Performance Guidelines discuss optimization strategies for a Mach-O executable. Building a Universal Binary See Also Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 20The PowerPC and the x86 architectures have some fundamental differences that can prevent code written for one architecture from running properly on the other architecture. The extent to which you need to change your PowerPC code so that it runs natively on an Intel-based Macintosh computer depends on how much of your code is processor specific. This chapter describes the major differences between architectures, organized alphabetically by topic. You can use the information to identify the parts of your code that are likely to be problematic. Alignment All PowerPC instructions are 4 bytes in size and must be 4-byte aligned. x86 instructions are variable in size (from 1 to >10 bytes), and as a consequence do not need to be aligned. Bit Fields The value of a signed, 1-bit bit field is either 0, 1, or –1, depending on the compiler, architecture, optimization level, and so forth. Code that compares the value of a bit field to 1 may not work if the bit field is signed, so you will want to use unsigned 1-bit bit fields. Keep in mind that the order of bit fields in memory can be reversed between architectures. For more information on issues related to endian format, see “Swapping Bytes” (page 26). See also “Archived Bit Fields” (page 46) and “Structures and Unions” (page 25). Byte Order Microprocessor architectures commonly use two different byte-ordering methods(little-endian and big-endian) to store the individual bytes of multibyte data formats in memory. This difference becomes critically important if you try to read data from filesthat were created on a computer that uses a different byte ordering than yours. You also need to consider byte ordering when you send and receive data through a network connection and handle networking data. The difference in byte ordering can produce incorrect results if you do not account for this difference. For example, the order of bytes in memory of a scalar type is architecture-dependent, as shown in Listing 2-1 (page 22). Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 21 Architectural DifferencesListing 2-1 Code that illustrates byte-ordering differences unsigned char charVal; unsigned long value = 0x12345678; unsigned long *ptr = &value; charVal = *(unsigned char*)ptr; On a processor that useslittle-endian addressing the variable charVal takes on the value 0x78. On a processor that uses big-endian addressing the variable charVal takes on the value 0x12. To make this code architecture-independent, change the last line in Listing 2-1 to the following: charVal = (unsigned char)*ptr; For a detailed discussion of byte ordering and strategies that you can use to account for byte-ordering differences, see “Swapping Bytes” (page 26). Calling Conventions The x86 C-language calling convention (application binary interface, or ABI)specifiesthat argumentsto functions are passed on the stack. The PowerPC ABI specifies that arguments to functions are passed in registers. Also, x86 has far fewer registers, so many local variables use the stack for their storage. Thus, programming errors, or other operationsthat access past the end of a local variable array or otherwise incorrectly manipulate values on the stack may be more likely to crash applications on x86 systems than on PowerPC. For detailed information about the IA-32 ABI, see Mac OS X ABI Function Call Guide . This document describes the function-calling conventions used in all the architecturessupported by Mac OS X. See also “32-Bit Application Binary Interface” (page 84). Code on the Stack: Disabling Execution Intel processors include a bit that prevents code from being executed on the stack. On Intel-based Macintosh computers, this bit is always set to On. Architectural Differences Calling Conventions Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 22Data Type Conversions For some data type conversions, such as casting a string to a long and converting a floating-point type to an integer type, the PowerPC and x86 architectures perform differently. When the microprocessor converts a floating-point type to an integer type, it discards the fractional part of the value. The behavior is undefined if the value of the integral part cannot be represented by the integer type. Listing 2-2 shows an example of the sort of code that is architecture-dependent. You would need to modify this code to make it architecture-independent. On a PowerPC microprocessor, the variable x shown in the listing is equal to 7fffffff or INTMAX. On an x86 microprocessor, the variable x is equal to 80000000 or INTMIN. Listing 2-2 Architecture-dependent code int main (int argc, const char * argv[]) { double a; int x; a = 5000000.0 * 6709000.5; // or any really big value x = a; printf("x = %08x \n",x); return 0; } Data Types A long double is 16 bytes on both architectures, but only 80 bits are significant in long double data types on Intel-based Macintosh computers. A bool data type is a single byte on an x86 system, but four bytes on a PowerPC architecture. Thissize difference can cause alignment problems. You should use fixed-size data types to avoid alignment problems. (The bool data type is not the Carbon Boolean type, which is a fixed size of 1 byte.) Existing document formats that include the bool data type as part of a data structure that is written directly to disk can be problematic because the data structure might not be laid out the same on both architectures. If you update the data structure definition to use the UInt32 data type or another fixed-size four-byte data type, the structure should then be portable, although you must swap bytes appropriately. Architectural Differences Data Type Conversions Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 23Divide-By-Zero Operations An integer divide-by-zero operation isfatal on an x86 system but the operation continues on a PowerPC system, where it returns zero. (A floating point divide-by-zero behaves the same on both architectures.) If you get a crash log that mentions EXC_I386_DIV (divide by zero), your program divided by zero. Mod operations perform a divide, so a mod-by-zero operation produces a divide-by-zero exception. To fix a divide-by-zero exception, find the place in your program corresponding to that operation. Then add code that checks for a denominator of zero before performing the divide operation. For example, change this: int a = b % c; // Divide by zero can happen here; to this: int a; if (c != 0) { a = b % c; } else { a = 0; } Extensible Firmware Interface (EFI) Intel-based Macintosh computers use extensible firmware interface (EFI). EFI provides a flexible and adaptable interface between Mac OS X and the platform firmware. This change should be transparent to most developers, but may affect some, such as those who write boot drivers. For more information on the EFI specification, see http://www.intel.com/technology/efi/ Floating-Point Equality Comparisons The results of a floating-point equality comparison are architecture-dependent. Whether the comparison works depends on a number of things, including the compiler, the surrounding code, all compiler flags in use (particularly optimization flags), and the current floating-point mode for the thread. If your floating-point comparison is currently working on PowerPC, you may need to inspect it on an Intel-based Macintosh computer. Architectural Differences Divide-By-Zero Operations Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 24You can use the GCC flag -Wfloat-equal to receive a warning for floating-point equality comparisons. For details on this option, see Section 3.8 of the GNU C/C++/Objective-C 4.0.1 Compiler User Guide Structures and Unions The fields in a structure can be sensitive to their defined order. Structures must either be properly ordered or accessed by the field name directly. When a union has components that could be affected by byte order, use a form similar to that shown in Listing 2-3. Code that sets wch and then reads hi and lo as the high and low bytes of wch will work correctly. The same is true for the reverse direction. Code that sets hi and lo and then reads wch will get the same value on both architectures. For another example, see the WideChar union that’s defined in the IntlResources.h header file. Listing 2-3 A union whose components can be affected by byte order union WChar{ unsigned short wch; struct { #if __BIG_ENDIAN__ unsigned char hi; unsigned char lo; #else unsigned char lo; unsigned char hi; #endif } s; } See Also The ISO standard for the C programming language—ISO/IEC 9899—is a valuable reference that you can use to investigate code portability issues, many of which may not be immediately obvious. You can find this reference in a number of locations on the web, including: http://www.iso.org/ Architectural Differences Structures and Unions Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 25Two primary byte-ordering methods (or endian formats) exist in the world of computing. An endian format specifies how to store the individual bytes of multibyte numerical data in memory. Big-endian byte ordering specifies to store multibyte data with its most significant byte first. Little-endian byte ordering specifies to store multibyte data with its least significant byte first. The PowerPC processor uses big-endian byte ordering. The x86 processor family uses little-endian byte ordering. By convention, multibyte data sent over the network uses big-endian byte ordering. If your application assumes that data is in one endian format, but the data is actually in another, then it will interpret the data incorrectly. You will want to analyze your code for routines that read multibyte data (16 bits, 32 bits, or 64 bits) from, or write multibyte data to, disk or to the network, as these routines are sensitive to byte-ordering format. There are two general approaches for handling byte ordering differences: swap bytes when necessary or use XML or another byte-order-independent data format such as those offered by Core Foundation (CFPreferences, CFPropertyList, CFXMLParser). Whether you should swap bytes or use a byte-order-independent data format depends on how you use the data in your application. If you have an existing file format to support, the binary-compatible solution is to accept the big-endian file format you have been using in your application, and write code that swaps bytes when the file isread or written on an Intel-based Macintosh. If you don’t have legacy filesto support, you could consider redesigning your file format to use XML (extensible markup language), XDR (external data representation), or NSCoding (Objective C) to represent data. This chapter describes why byte ordering matters, gives guidelines for swapping bytes, describes the byte-swapping APIs available in Mac OS X, and providessolutionsfor most of the situations where byte ordering matters. Why Byte Ordering Matters The example in this section is designed to show you why byte ordering matters. Take a look at the C data structure defined in Listing 3-1. It contains a four-byte integer, a character string, and a two-byte integer. The listing also initializes the structure. Listing 3-1 A data structure that contains multibyte and single-byte data typedef struct { Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 26 Swapping Bytesuint32_t myOptions; char myStringArray [7]; short myVariable; } myDataStructure; myDataStructure aStruct; aStruct.myOptions = 0xfeedface; strcpy(aStruct.myStringArray, "safari"); aStruct.myVariable = 0x1234; Figure 3-1 compares how this data structure is stored in memory on big-endian and little-endian systems. In a big-endian system, memory is organized with the address of each data byte increasing from most significant to leastsignificant. In a little-endian system, memory is organized with the address of each data byte increasing from the least significant to the most significant. Figure 3-1 Big-endian byte ordering compared to little-endian byte ordering 0x00000004 0x00000005 0x00000006 0x00000007 0x00000008 0x00000009 0x0000000A 0x0000000B 0x0000000C 0x0000000D 0x0000000E 0x0000000F fe fe ed fa ed fa ce ce 's' 's' 'a' 'a' 'a' 'a' 'f' 'f' 'r' 'r' 'i' 'i' 12 34 12 34 \0 \0 0x00000000 0x00000001 0x00000002 0x00000003 Address Data * * * Big-endian 0x00000004 0x00000005 0x00000006 0x00000007 0x00000008 0x00000009 0x0000000A 0x0000000B 0x0000000C 0x0000000D 0x0000000E 0x0000000F 0x00000000 0x00000001 0x00000002 0x00000003 Address Data * * * Little-endian Padding bytes used to maintain alignment As you look at Figure 3-1, note the following: Swapping Bytes Why Byte Ordering Matters Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 27● Multibyte data, such as the 32-bit and 16-bit variables shown in the figure, are stored differently between big-endian and little-endian systems. As you can see in the figure, big-endian systemsstore data in memory so that the most significant byte of the data is stored in the address with the lowest value. Little-endian systems store data in memory so that the most significant byte of the data is in the address with the highest value. Hence, the least significant byte of the myOptions variable (0xce) is stored in memory location 0x00000003 on the big-endian system while it is stored in memory location 0x00000000 on the little-endian system. ● Single-byte data, such as the char values in the myStringArray character array, are stored in the same memory location on either system regardless of the byte ordering format of the system. ● Each system pads bytes to maintain four-byte data alignment. Padded bytes in the figure are designated by a shaded box that contains an asterisk. The byte ordering of multibyte data in memory matters if you are reading data written on one architecture from a system that uses a different architecture and you access the data on a byte-by-byte basis. For example, if your application is written to access the second byte of the myOptions variable, then when you read the data from a system that uses the opposite byte ordering scheme, you’ll end up retrieving the first byte of the myOptions variable instead of the second one. Suppose the example data values that are initialized by the code shown in Listing 3-1 are generated on a little-endian system and saved to disk. Assume that the data is written to disk in byte-address order. When read from disk by a big-endian system, the data is again laid out in memory asshown in Figure 3-1. The problem is that the data is still in little-endian byte order even though it is interpreted on a big-endian system. This difference causes the values to be evaluated incorrectly. In this example, the value of the field myOptions should be 0xfeedface, but because of the incorrect byte ordering it is evaluated as 0xcefaedfe. Note: The terms big-endian and little-endian come from Jonathan Swift’s eighteenth-century satire Gulliver’s Travels. The subjects of the empire of Blefuscu were divided into two factions: those who ate eggs starting from the big end and those who ate eggs starting from the little end. Guidelines for Swapping Bytes The following guidelines, along with the strategies provided later in this chapter, will help ensure optimal byte-swapping code in your application. ● Keep data structures in native byte-order while in memory. Only swap bytes when you read data from disk or write it to disk. Swapping Bytes Guidelines for Swapping Bytes Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 28● When possible, let the compiler do the work for you. For example, when you use function calls such as the Core Foundation function CFSwapInt16BigToHost, the compiler determines whether the function call does something for the processor you are targeting. If the code does nothing, the compiler won’t call the function. Letting the compiler do the work is more efficient than using #ifdef statements. ● If you must access a large file, consider arranging the data in a way that limits the byte swapping that you must perform. For example, you can arrange the most frequently accessed data contiguously in the file. Then, you need to read and swap bytes only for that chunk of data instead of for the entire data file. ● Use the __BIG_ENDIAN__ and __LITTLE_ENDIAN__ macros only if you must. Do not use macros that check for a specific processor type, such as __i386__ and __ppc__. ● Choose a consistent byte-order approach and stick with it. That is, if you are reading and writing data from disk on a regular basis, choose the endian format you want to use. This eliminates the need for you to check the byte ordering of the data, and then to possibly have to swap the byte order. ● Be aware of which functions return big-endian data, and use them appropriately. These include the BSD Sockets networking functions, the DNSServiceDiscovery functions (for example, TCP and UDP ports are specified in network byte order), and the ColorSync profile functions (for which all data is big-endian). The IconFamilyElement and IconFamilyResource data types (which also include the data types IconFamilyPtr and IconFamilyHandle) are always big-endian. There may be other functions and data types that are not listed here. Consult the appropriate API reference for information on data returned by a function. For more information see “Network-Related Data” (page 34). ● Keep in mind that swapping bytes comes at a performance cost so swap them only when absolutely necessary. Byte-Swapping Routines The APIs that provide byte-swapping routines are listed below. For most situations it’s best to use the routines that match the framework you’re programming in. The Core Foundation and Foundation APIs have functions for swapping floating-point values, while the other APIs listed do not. ● POSIX (Portable Operating System Interface) byte ordering functions (ntohl, htonl, ntohs, and htons) are documented in Mac OS X Man Pages. ● Darwin byte ordering functions and macros are defined in the header file libkern/OSByteOrder.h. Even though this header is in the kernel framework, it is acceptable to use it from high-level applications. ● Core Foundation byte-order functions are defined in the header file CoreFoundation/CFByteOrder.h and described in the Byte-Order Utilities Reference . For details on using these functions, see the Byte Swapping article in Memory Management Programming Guide for Core Foundation . ● Foundation byte-order functions are defined in the header file Foundation/NSByteOrder.h and described in Foundation Framework Reference . Swapping Bytes Byte-Swapping Routines Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 29● The Core Endian API is defined in the header file CarbonCore/Endian.h and described in Core Endian Reference . Note: When you use byte-swapping routines, the compiler optimizes your code so that the routines are executed only if they are needed for the architecture on which your code is running. Byte-Swapping Strategies The strategy for swapping bytes depends on the format of the data; there is no universal routine that can take care of all byte ordering differences. Any program that needsto swap data must know the data type, the source data endian order, and the host endian order. This section lists byte-swapping strategies, organized alphabetically, for the following data: ● “Constants” (page 30) ● “Custom Apple Event Data” (page 31) ● “Custom Resource Data” (page 31) ● “Floating-Point Values” (page 32) ● “Integers” (page 33) ● “Network-Related Data” (page 34) ● “OSType-to-String Conversions” (page 35) ● “Unicode Text Files” (page 36) ● “Values in an Array” (page 38) Constants Constants that are part of a compiled executable are in host byte order. You need to swap bytes for a constant only if it is part of data that is not maintained natively or if the constant travels between hosts. In most cases you can either swap bytes ahead of time or let the preprocessor perform any needed math by using shifts or other simple operators. If you are defining and populating a structure that must use data of a specific endian format in memory, use the OSSwapConst macros and the OSSwap*Const variants defined in the libkern/OSByteOrder.h header file. These macros can be used from high-level applications. Swapping Bytes Byte-Swapping Strategies Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 30Custom Apple Event Data An Apple event is a high-level event that conforms to the Apple Event Interprocess Messaging Protocol. The Apple Event Managersends Apple events between applications on the same computer or between applications on remote computers. You can define your own Apple event data types, and send and receive Apple events using the Apple Event Manager API. Mac OS X manages system-defined Apple event data types for you, handling them appropriately for the currently executing code. You don't need to perform any special tasks. When the data that your application extracts from an Apple event is system-defined, the system swaps the data for you before giving the event to your application to process. You will want to treat system-defined data types from Apple events as native endian. Similarly, if you put native-endian data into an Apple event that you are sending, and it is a system-defined data type, the receiver will be able to interpret the data in its own native endian format. However, you must account for byte-ordering differences for the custom Apple event data types that you define. You can accomplish this in one of the following ways: ● Write a byte-swapping callback routine (also known as a flipper) and provide it to the system. Whenever the system determines that your Apple event data needs to be byte swapped it invokes your flipper to ensure that the recipient of the data gets the data in the correct endian format. For details, see “Writing a Callback to Swap Data Bytes” (page 38). ● Choose one endian format to use, regardless of architecture. Then, when you read or write your custom Apple event data, use big-to-host and host-to-big routines,such asthe Core Foundation Byte Order Utilities functions CFSwapInt16BigToHost and CFSwapInt16HostToBig. Custom Resource Data In Mac OS X, the preferred way to supply resources is to provide files in your application bundle that define resources such as image files, sounds, localized text, and archived user-interface definitions. The resource data types discussed in this section are those defined in Resource Manager-style files supported by Carbon. The Resource Manager was created prior to Mac OS X. If your application uses Resource Manager-style resource files, you should consider moving towards Mac OS X–style resources in your application bundle instead. Resources typically include data that describes menus, windows, controls, dialogs, sounds, fonts, and icons. Although the system defines a number ofstandard resource types(such as 'moov', used to specify a QuickTime movie, and 'MENU', used to define menus) you can also create your own private resource types for use in your application. You use the Resource Manager API to define resource data types and to get and set resource data. Mac OS X keepstrack of resourcesin memory and allows your application to read or write resources. Applications and system software interpret the data for a resource according to its resource type. Although you'll typically let the operating system read resources (such as your application icon) for you, you can also call Resource Manager functions directly to read and write resources. Swapping Bytes Byte-Swapping Strategies Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 31Mac OS X manages the system-defined resources for you, handling them appropriately for the currently executing code. That is, if your application runs on an Intel-based Macintosh, Mac OS X swaps bytes so that your application icon, menus, and other standard resources appear correctly. You don't need to perform any special tasks. But if you define your own private resource data types for use in your application, you need to account for byte-ordering differences between architectures when you read or write resource data from disk. You can use either of the following strategies to handle custom Resource Manager-style resource data. Notice that these are the same strategies used to handle custom Apple event data: ● Provide a byte-swapping callback routine for the system to invoke whenever the system determines your resource data must be byte swapped. For details, see “Writing a Callback to Swap Data Bytes” (page 38). ● Always write your data using the same endian format, regardless of the architecture. Then, when you read or write your custom resource data, use big-to-host and host-to-big routines, such as the Core Foundation Byte Order Utilities CFSwapInt16BigToHost and CFSwapInt16HostToBig. Note: If you are revising old code that marks resources with a preload bit, you should remove the preload bit from any resources that must be byte swapped. In Mac OS X, the preload bit is almost always unnecessary. If you cannot remove the preload bit, you should swap the resource data after you read the resource. You will not be able to use a flipper callback to swap bytes automatically because in Mac OS X a preload bit causes the resources to be read before any of the application code runs. Floating-Point Values Core Foundation defines a set of functions and two special data types to help you work with floating-point values. These functions allow you to encode 32- and 64-bit floating-point values in such a way that they can later be decoded and byte swapped if necessary. Listing 3-2 shows you how to encode a 64-bit floating-point number and Listing 3-3 shows how to decode it. Listing 3-2 Encoding a 64-bit floating-point value double d = 3.0; CFSwappedFloat64 swappedDouble; // Encode the floating-point value. swappedDouble = CFConvertFloat64HostToSwapped(d); // Call the appropriate routine to write swappedDouble to disk, // send it to another process, etc. write(myFile, &swappedDouble, sizeof(swappedDouble)); Swapping Bytes Byte-Swapping Strategies Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 32The data types CFSwappedFloat32 and CFSwappedFloat64 contain floating-point values in a canonical representation. A CFSwappedFloat data type is not itself a floating-point value, and should not be directly used as one. You can however send one to another process, save it to disk, or send it over a network. Because the format is converted to and from the canonical format by the conversion functions, there is no need for explicit swapping. Bytes are swapped for you during the format conversion if necessary. Listing 3-3 Decoding a 32-bit floating-point value float f; CFSwappedFloat32 swappedFloat; // Call the appropriate routine to read swappedFloat from disk, // receive it from another process, etc. read(myFile, &swappedFloat, sizeof(swappedFloat)); f = CFConvertFloat32SwappedToHost(swappedFloat) The NSByteOrder.h header file defines functions that are comparable to the Core Foundation functions discussed here. Integers The system library byte-access functions, such as OSReadLittleInt16 and OSWriteLittleInt16, provide generic byte swapping. These functions swap bytes if the native endian format is different from the endian format of the destination. They are defined in the libkern/OSByteOrder.h header file. Note: The OSReadXXX and OSWriteXXX functions provide higher performance than the OSSwapXXX functions or any other functions in the higher-level frameworks. Core Foundation provides three optimized primitive functions for swapping bytes— CFSwapInt16, CFSwapInt32, and CFSwapInt64. All of the other swapping functions use these primitives to accomplish their work. In general you don’t need to use these primitives directly. Although the primitive swapping functions swap unconditionally, the higher-level swapping functions are defined in such a way that they do nothing when swapping bytes is not required—in other words, when the source and host byte orders are the same. For the integer types, these functions take the forms CFSwapXXXBigToHost, CFSwapXXXLittleToHost, CFSwapXXXHostToBig, and CFSwapXXXHostToLittle, where XXX is a data type such as Int32. For example, on a little-endian machine you use the function CFSwapInt16BigToHost to read a 16-bit integer value from a network whose data is in network byte order (big-endian). Listing 3-4 demonstrates this process. Swapping Bytes Byte-Swapping Strategies Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 33Listing 3-4 Swapping a 16-bit integer from big-endian to host-endian SInt16 bigEndian16; SInt16 swapped16; // Swap a 16-bit value read from the network. swapped16 = CFSwapInt16BigToHost(bigEndian16); Suppose the integers are in the fields of a data structure. Listing 3-5 demonstrates how to swap bytes. Listing 3-5 Swapping integers from little-endian to host-endian // Swap the bytes of the values if necessary. aStruct.int1 = CFSwapInt32LittleToHost(aStruct.int1) aStruct.int2 = CFSwapInt32LittleToHost(aStruct.int2) The code swaps bytes only if necessary. If the host is a big-endian architecture, the functions used in the code sample swap the bytesin each field. The code does nothing when run on a little-endian machine—the compiler ignores the code. Network-Related Data Network-related data typically uses big-endian format (also known as network byte order), so you may need to swap bytes when communicating between the network and an Intel-based Macintosh computer. You probably never had to adjust your PowerPC code when you transmitted data to, or received data from, the network. On an Intel-based Macintosh computer you must look closely at your networking code and ensure that you always send network-related data in the appropriate byte order. You must also handle data received from the network appropriately, swapping the bytes of values to the endian format appropriate to the host microprocessor. You can use the following POSIX functions to convert between network byte order and host byte order. (Other byte-swapping functions, such as those defined in the OSByteOrder.h and CFByteOrder.h header files, can also be useful for handling network data.) ● network to host: uint32_t ntohl (uint32_t netlong); uint16_t ntohs (uint16_t netshort); ● host to network: uint32_t htonl (uint32_t hostlong); Swapping Bytes Byte-Swapping Strategies Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 34uint16_t htons (uint16_t hostshort); These functions are documented in Mac OS X Man Pages. The sin_saddr.s_addr and sin_port fields of a sockaddr_in structure should always be in network byte order. You can find out the appropriate endian format of any argument to a BSD networking function by reading the man page documentation. When advertising a service on the network, you use getsockname to get the local TCP or UDP port that your socket is bound to, and then pass my_sockaddr.sin_port unchanged, without any byte swapping, to the DNSServiceRegister function. In CoreFoundation code, you can use the same approach. Use the CFSocketCopyAddress function as shown below, and then pass my_sockaddr.sin_port unchanged, without any byte swapping, to the DNSServiceRegister function. CFDataRef addr = CFSocketCopyAddress(myCFSocketRef); struct sockaddr_in my_sockaddr; memmove(&my_sockaddr, CFDataGetBytePtr(addr), sizeof(my_sockaddr)); DNSServiceRegister( ... , my_sockaddr.sin_port, ...); When browsing and resolving, the process is similar. The DNSServiceResolve function and the BSD Sockets calls such as gethostbyname and getaddrinfo all return IP addresses and ports already in the correct byte order so that you can assign them directly to your struct sockaddr_in and call connect to open a TCP connection. If you byte-swap the address or port, then your program will not work. The important point is that when you use the DNSServiceDiscovery API with the BSD Sockets networking APIs, you do not need to swap anything. Your code will work correctly on both PowerPC and Intel-based Macintosh computers as well as on Linux, Solaris, and Windows. OSType-to-String Conversions You can use the functions UTCreateStringForOSType and UTGetOSTypeFromString to convert an OSType data type to or from a CFString object (CFStringRef data type). These functions are discussed in Uniform Type Identifiers Overview and defined in the UTType.h header file, which is part of the Launch Services framework. When you use four-character literals, keep in mind that "abcd" != 'abcd'. Rather 'abcd' == 0x61626364. You must treat 'abcd' as an integer and not string data, as 'abcd' is a shortcut for a 32-bit integer. (A FourCharCode data type is a UInt32 data type.) The compiler does not swap this for you. You can use the shift operator if you need to deal with individual characters. Swapping Bytes Byte-Swapping Strategies Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 35For example, if you currently print an OSType or FourCharCode type using the standard C printf-style semantics, use printf("%c%c%c%c", (char) (val >> 24), (char) (val >> 16), (char) (val >> 8), (char) val) instead of the following: printf("%4.4s", (const char*) &val) Unicode Text Files Mac OS X often uses UTF-16 to encode Unicode; a UniChar data type is a double-byte value. As with any multibyte data, Unicode characters are sensitive to the byte ordering method used by the microprocessor. A byte order mark written to the beginning of a file informs the program reading the data which byte ordering method was used to write the data. The Unicode standard states that in the absence of a byte order mark (BOM) the data in a Unicode data file is to be taken as big-endian. Although a BOM is not mandatory, you should make use of it to ensure that a file written on one architecture can be read from the other architecture. The program can then act accordingly to make sure the byte ordering of the Unicode text is compatible with the host. Table 3-1 lists the standard byte order marks for UTF-8, UTF-16, and UTF-32. (Note that the UTF-8 BOM is not used for endian issues, but only as a tag to indicate that the file is UTF-8.) Table 3-1 Byte order marks Byte order mark Encoding form EF BB BF UTF-8 FF FE UTF-16/UCS-2, little endian FE FF UTF-16/UCS-2, big endian FF FE 00 00 UTF-32/UCS-4, little endian 00 00 FE FF UTF-32/UCS-4, big endian In practice, when your application reads a file, it does not need to look for a byte order mark nor does it need to swap bytes as long as you follow these steps to read a file: 1. Map the file using mmap to get a pointer to the contents of the file (or string). Swapping Bytes Byte-Swapping Strategies Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 36Reading the entire file into memory ensures the best performance and is a prerequisite for the next step. 2. Generate a CFString object by calling the function CFStringCreateWithBytes with the isExternalRepresentation parameter set to true, or call the function CFStringCreateWithExternalRepresentation to generate a CFString, passing in an encoding of kCFStringEncodingUnicode (for UTF-16) or kCFStringEncodingUTF8 (for UTF-8). Either function interprets a BOM swaps bytes as necessary. Note that a BOM should not be used in memory; its use is solely for data transmission (files, pasteboard, and so forth). In summary, with respect to Unicode files, your application performs best when you follow these guidelines: ● Accept the BOM when taking UTF-16 or UTF-8 encoded files from outside the application. ● Use native-endian UniChar data types internally. ● Generate a BOM when writing UTF-16 to a file. Ideally, you only need to generate a BOM for an architecture that uses little-endian format, but it is also acceptable to generate a BOM for an architecture that uses big-endian format. ● When you put data on the Clipboard, make sure that 'utxt' data does not have a BOM. Only 'ut16' data should have a BOM. If you use Cocoa to put an NSString object on the pasteboard, you don’t need to concern yourself with a BOM. For more information, see “UTF & BOM,” available from the Unicode website: http://www.unicode.org/faq/utf_bom.html The Apple Event Manager provides text constants that you can use to specify the type of your data. As of Mac OS X v10.4, only two text constants are recommended: ● typeUTF16ExternalRepresentation, which specifies Unicode text in 16-bit external representation with optional byte order mark (BOM). The presence of this constant guarantees that either there is a BOM or the data is in UTF-16 big-endian format. ● typeUTF8Text, which specifies 8-bit Unicode (UTF-8 encoding). The constant typeUnicodeText indicates utxt text data, in native byte ordering format, with an optional BOM. This constant does not specify an explicit Unicode encoding or byte order definition. The Scrap Manager provides the flavor type constant kScrapFlavorTypeUTF16External which specifies Unicode text in 16-bit external representation with optional byte order mark (BOM). Swapping Bytes Byte-Swapping Strategies Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 37Values in an Array The routine in Listing 3-6 shows an approach that you can use to swap the bytes of values in an array. On a big-endian system, the compiler optimizes away the entire function; you don’t need to use #ifdef statements to swap these sorts of arrays. Listing 3-6 A routine for swapping the bytes of the values in an array static inline void SwapUInt32ArrayBigToHost(UInt32 *array, UInt32 count) { int i; for(i = 0; i < count; i++) { array[i] = CFSwapInt32BigToHost(array[i]); } } Writing a Callback to Swap Data Bytes You can provide a byte-swapping callback routine, also referred to as a flipper, to the system for custom resource data, custom pasteboard data, and custom Apple event data. When you install a byte-swapping callback, you specify which domain that the data type belongs to. There are two data domains—Apple event and resource. The resource data domain specifies custom pasteboard data or custom resource data. If the callback can be applied to either domain (Apple event and resource), you can specify that as well. The Core Endian API defines a callback that you provide to swap bytes for custom resource and Apple event data. You must provide one callback for each type of data you want to swap bytes. The prototype for the CoreEndianFlipProc callback is: typedef CALLBACK_API (OSStatus, CoreEndianFlipProc) (OSType dataDomain, OSType dataType, short id, void *dataPtr, UInt32 dataSize, Boolean currentlyNative, void *refcon ); Swapping Bytes Writing a Callback to Swap Data Bytes Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 38The callback takes the following parameters: ● dataDomain—An OSType value thatspecifiesthe domain to which the flipper callback applies. The value kCoreEndianResourceManagerDomain signifies that the domain is resource or pasteboard data. The value kCoreEndianAppleEventManagerDomain signifies that the domain is Apple event data. ● dataType—The type of data that needs the callback to swap bytes for. This is the four-character code of the resource type, pasteboard type, or Apple event. ● id—The resource id of the data type. This field is ignored if the dataDomain parameter is not kCoreEndianResourceManagerDomain. ● dataPtr—On input, points to the data to be flipped. On output, points to the byte swapped data. ● dataSize—The size of the data pointed to by the dataPtr parameter. ● currentlyNative—A Boolean value that indicatesthe direction to swap bytes. The value true specifies the data pointed to by the dataPtr parameter uses the byte ordering of the currently executing code. On a PowerPC Macintosh, true specifiesthat the data isin big-endian format. On an Intel-based Macintosh, true specifies that the data is in little-endian format. ● refcon—A 32-bit value that contains, or refers to, data needed by the callback. The callback returns a result code that indicates whether bytes are swapped successfully. Your callback should return noErr if the data is byte swapped without error and the appropriate result code to indicate an error condition—errCoreEndianDataTooShortForFormat, errCoreEndianDataTooLongForFormat, or errCoreEndianDataDoesNotMatchFormat. The result code you return is propagated through the appropriate manager (Resource Manager (ResError) or Apple Event Manager) to the caller. You do not need to swap bytes for quantities that are not numerical (such as strings, byte streams, and so forth). You need to provide a callback only to swap bytes data types for which the order of bytes in a word or long word are important. (For the preferred way to handle Unicode strings, see “Unicode Text Files” (page 36).) Your callback should traverse the data structure that contains the data and swap bytes for: ● All counts and lengths so that array indexes are associated with the appropriate value ● All integers and longs so that when you read them into variables of a compatible type, you can operate correctly on the values (such as numerical, offset, and shift operations) The Core Endian API provides these functions for working with your callback: ● CoreEndianInstallFlipper registers your callback for the specified data type (custom resource or custom Apple Event). After you register a byte-swapping callback for an application-defined resource data type, then any time you call a Resource Manager function that operates on that resource type, the system invokes your callback if it is appropriate to do so. (If your callback operates on pasteboard data, the system Swapping Bytes Writing a Callback to Swap Data Bytes Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 39also invokes the callback at the appropriate time.) Similarly, if you specify Apple event as the domain for your callback, then any time you call an Apple Event Manager function that operates on that data type, your callback is invoked when it is appropriate to do so. ● CoreEndianGetFlipper obtains the callback that is registered for the specified data type. You can call this function to determine whether a flipper is available for a given data type. ● CoreEndianFlipData invokes the callback associated with the specified data type. You shouldn’t need to call this function, because the system invokes your callback whenever it’s needed. As an example, look at a callback for the custom resource type ('PREF') defined in Listing 3-7. The MyPreferences structure is used to store preferences data on disk. The structure contains a number of values and includes two instances of the RGBColor data type and an array of RGBColor values. Listing 3-7 A declaration for a custom resource #define kMyPreferencesType 'PREF' struct MyPreferences { SInt32 fPrefsVersion; Boolean fHighlightLinks; Boolean fUnderlineLinks; RGBColor fHighlightColor; RGBColor fUnderlineColor; SInt16 fZoomValue; char fCString[32]; SInt16 fCount; RGBColor fPalette[]; }; You can handle the RGBColor data type by writing a function thatswaps bytesin an RGBColor data structure, such as the function MyRGBSwap, shown in Listing 3-8. This function calls the Core Endian macro EndianS16_Swap to swap bytes for each of the values in the RGBColor data structure. The function doesn’t need to check for the currently executing system because the function is never called unless the values in the Swapping Bytes Writing a Callback to Swap Data Bytes Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 40RGBColor data type need to have their bytesswapped. The MyRGBSwap function is called by the byte-swapping callback routine (shown in Listing 3-9 (page 41)) that’s provided to handle the custom 'PREF' resource (that is defined in Listing 3-7 (page 40)). Listing 3-8 A flipper function for RGBColor data static void MyRGBSwap (RGBColor *p) { p->red = Endian16_Swap(p->red); p->blue = Endian16_Swap(p->blue); p->green = Endian16_Swap(p->green); } Listing 3-9 shows a byte-swapping callback for the custom 'PREF' resource. An explanation for each numbered line of code appears following the listing. Note that the flipper checks for data that is malformed or is of an unexpected length. If the data passed into the flipper routine is a shorter length than the flipped type is normally, or (for example) contains garbage data instead of an array count, the flipper must be careful not to read or write data beyond the end of the passed-in data. Instead, the routine returns an error. Listing 3-9 A flipper for the custom 'PREF' resource #define kCurrentVersion 0x00010400 static OSStatus MyFlipPreferences (OSType dataDomain, // 1 OSType dataType, // 2 short id, // 3 void * dataPtr, // 4 UInt32 dataSize, // 5 Boolean currentlyNative, // 6 void* refcon) // 7 { UInt32 versionNumber; OSStatus status = noErr; MyPreferences* toFlip = (MyPreferences*) dataPtr; // 8 int count, i; Swapping Bytes Writing a Callback to Swap Data Bytes Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 41if (dataSize < sizeof(MyPreferences)) return errCoreEndianDataTooShortForFormat; // 9 if (currentlyNative) // 10 { count = toFlip->fCount; versionNumber = toFlip->fPrefsVersion; toFlip->fPrefsVersion = Endian32_Swap (toFlip->fPrefsVersion); toFlip->fCount = Endian16_Swap (toFlip->fCount); toFlip->fZoomValue = Endian16_Swap (toFlip->fZoomValue); } else // 11 { toFlip->fPrefsVersion = Endian32_Swap (toFlip->fPrefsVersion); versionNumber = toFlip->fPrefsVersion; toFlip->fCount = Endian16_Swap (toFlip->fCount); toFlip->fZoomValue = Endian16_Swap (toFlip->fZoomValue); count = toFlip->fCount; } if (versionNumber != kCurrentVersion) // 12 return errCoreEndianDataDoesNotMatchFormat; MyRGBSwap (&toFlip->fHighlightColor); // 13 MyRGBSwap (&toFlip->fUnderlineColor); // 14 if (dataSize < sizeof(MyPreferences) + count * sizeof(RGBColor)) return errCoreEndianDataTooShortForFormat; // 15 for(i = 0; i < count; i++) { MyRGBSwap (&toFlip->fPalette[i]); // 16 } return status; // 17 } Swapping Bytes Writing a Callback to Swap Data Bytes Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 42Here’s what the code does: 1. The system passesto your callback the domain to which the callback applies. You define the domain when you register the callback using the function CoreEndianInstallFlipper. 2. The system passesto your callback the resource type you defined for the data. In this example, the resource type is 'PREF'. 3. The system passes to your callback the resource ID of the data type. If the data is not a resource, this value is 0. 4. The system passes to your callback a pointer to the resource data that needs to have its bytes swapped. In this case, the pointer refers to a MyPreferences data structure. 5. The system passes to your callback the size of the data pointed to by the pointer described in the previous step. 6. The system passes to your callback true if the data in the buffer passed to the callback is in the byte ordering of the currently executing code. On a PowerPC Macintosh, when currentlyNative is true, the data isin big-endian order. On a Macintosh that uses an Intel microprocessor, when currentlyNative is true, the data is in little-endian order. Your callback needs to know this value, because if your callback uses a value in the data buffer to decide how to process other data in the buffer (for example, the count variable shown in the code), you must know whether that value needs to be flipped before the value can be used by the callback. 7. The system passes to your callback a pointer that refers to application-specific data. In this example, the callback doesn’t require any application-specific data. 8. Defines a variable for the MyPreferences data type and assigns the contents of the data pointer to the newly-defined toFlip variable. 9. Checks the static-length portion of the structure. If the size is less than it should be, the routine returns the error errCoreEndianDataTooLongForFormat. 10. If currentlyNative is true, saves the count value to a local variable and then swaps the bytes for the other values in the MyPreferences data structure. You must save the count value before you swap because you need it for an iteration later in the function. The fact that currentlyNative is true indicates that the value does not need to be byte swapped if it is used in the currently executing code. However, the value does need to be swapped to be stored to disk. The values are swapped using the appropriate Core Endian macros. 11. If currentlyNative is false, flips the values in the MyPreferences data structure before it saves the count value to a local variable. The fact that currentlyNative is false indicates that the count value needs to have its bytes swapped before it can be used in the callback. 12. Checks to make sure the version of the data structure is supported by the application. If the version is not supported, then your callback would not swap bytes for the data and would return the result errCoreEndianDataDoesNotMatchFormat. Swapping Bytes Writing a Callback to Swap Data Bytes Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 4313. Callsthe MyRGBSwap function (shown in Listing 3-8 (page 41)) to swap the bytes of the fHighlightColor field of the data structure. 14. Calls the MyRGBSwap function to swap the bytes of the fUnderlineColor field of the data structure. 15. Checks the data size to make sure that it is less than it should be. If not, the routine returns the error errCoreEndianDataTooLongForFormat. 16. Iterates through the elements in the fPalette array, calling the MyRGBSwap function to swap the bytes of the data in the array. 17. Returns noErr to indicate that the data is flipped without error. Although the sample performs some error checking, it does not include all the error-handling code that it could. When you write a flipper you may want to include such code. Note: The callback does not flip any of the Boolean values in the MyPreferences data structure because these are single character values. The callback also ignores the C string. You register a byte-swapping callback routine by calling the function CoreEndianInstallFlipper. You should register the callback when your application callsitsinitialization routine or when you open your resources. For example, you would register the flipper callback shown in Listing 3-9 (page 41) using the following code: OSStatus status = noErr; status = CoreEndianInstallFlipper (kCoreEndianResourceManagerDomain, kMyPreferencesType, MyFlipPreferences, NULL); The system invokes the callback for the specified resource type and data domain when currentlyNative is false at the time a resource is loaded and true at the time the resource is set to be written. For example, the sample byte-swapping callback gets invoked any time the following line of code is executed in your application: MyPreferences** hPrefs = (MyPreferences**) GetResource ('PREF', 128); After swapping the bytes of the data, you can modify it as much as you’d like. Swapping Bytes Writing a Callback to Swap Data Bytes Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 44When the Resource Manager reads a resource from disk, it looks up the resource type (for example, 'PREF') in a table of byte-swapping routines. If a callback is installed for that resource type, the Resource Manager invokes the callback if it is appropriate to do so. Similar actions are taken when the Resource Manager writes a resource to disk. It finds the appropriate routine and invokes the callback to swap the bytes of the resource if it is appropriate to do so. When you copy or drag custom data from an application that has a callback installed for pasteboard data, the system invokes your callback at the appropriate time. If you copy or drag custom data to a native application, the data callback is not invoked. If you copy or drag custom data to a nonnative application, the system invokes your callback to swap the bytes of the custom data. If you paste or drop custom data into your application from a nonnative application, and a callback exists for that custom data, the system invokes the callback at the time of the paste or drop. If the custom data is copied or dragged from another native application, the callback is not invoked. Note that different pasteboard APIs use different type specifiers. The Scrap Manager and Drag Manager use OSType data types. The Pasteboard Manager uses Uniform Type Identifiers(UTI), and the NSPasteboard class uses its own type mechanism. In each case, the type is converted by the system to an OSType data type to discover if there is a byte-swapping callback for that type. Apple event data types are typically swapped to network byte order when sent over a network. The callback you install is called only if a custom data type that you define issent to another machine, or if another machine sends Apple event data to your application. The byte ordering of Apple events on the network is big-endian. For casesin which the system would not normally invoke your byte-swapping callback, you can call the function CoreEndianFlipData to invoke the callback function installed for the specified data type and domain. See Also The following resources are available in the ADC Reference Library: ● Byte-Order Utilities Reference describes the Core Foundation byte order utilities API. ● Byte Swapping, in Core Foundation Memory Management, shows how to swap integers and floating-point values using Core Foundation byte-order utilities. ● File-System Performance Guidelines provides information useful for mapping Unicode files to memory. Swapping Bytes See Also Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 45This chapter lists an assortment ofscenariosthat relate to a specific technology or API. Although many of these scenarios are uncommon, you will want to at least glance at the topics to determine whether anything applies to your application. The topics are organized alphabetically. Aliases Aliases are big-endian on all systems. Applications that add extra information to the end of an AliasHandle must ensure that the extra data is always endian-neutral or of a defined endian type, preferably big-endian. The AliasRecord data structure is opaque when building your application with the Mac OS X v10.4(Universal) SDK. Code that formerly accessed the userType field of an AliasRecord must use the Alias Manager functions GetAliasUserType, GetAliasUserTypeFromPtr, SetAliasUserType, or SetAliasUserTypeFromPtr. Code that formerly accessed the aliasSize field of an AliasRecord must use the functions GetAliasSize or GetAliasSizeFromPtr. These Alias Manger functions are available in Mac OS X v10.4 and later. For more information,see Alias Manager Reference . Archived Bit Fields For cross platform portability, avoid using bit fields. It’s best not to use the NSArchiver class to archive any structures that contain bit fields as integers. Individual values are stored in the archives in an architecture and compiler dependent manner. In cases where archives already contain such structures, you can read a structure correctly by changing its declaration so that the bit fields are swapped appropriately Automator Scripts AppleScript actions are platform-independent and do not need any changes to run on Intel-based Macintosh computers. However, any action that contains Cocoa code, whether it is a solely Cocoa action or an action that uses both AppleScript and Cocoa code, must be built as a universal binary to run correctly on both architectures. For more information, see Automator Programming Guide . Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 46 Guidelines for Specific ScenariosBit Shifting When you shift a value by the width of itstype or more, the fill bits are undefined regardless of the architecture. In fact, two different compilers on the same architecture could differ on the value of y after these two statements: uint32_t x = 0xDEADBEEF; uint32_t y = x >> 32; Bit Test, Set, and Clear Functions: Carbon and POSIX Don’t mix using the C bitwise operators with the Carbon functions BitTst, BitSet, and BitClr and the POSIX macros setbit, clrbit, isset, and isclr. If you consistently use the Carbon and POSIX functions and avoid the C bitwise operators, your code will function properly. Keep in mind, however, that you must use the Carbon and POSIX functions on the correct kind of data. The Carbon and POSIX functions perform a byte-by-byte traversal, which causes problems on an Intel-based Macintosh when they operate on data types that are larger than 1 byte. You can use these functions only on a pointer to a string of endian-neutral bytes. When you need to perform bit manipulation on integer values you should use functions such as (int32 & (1 << 26)) instead of BitTst(&int32, 5L). You’ll encounter problems when you use the function BitTst to test for 24-bit mode. For example, the following bit test returns false, which indicates that the process is running in 24-bit mode, or at least that the code is not running in 32-bit mode. The POSIX equivalents perform similarly: Gestalt(gestaltAddressingModeAttr, &gestaltResult); if (!(BitTst(&gestaltResult,31L)) ) /*If 24 bit You can use any of the bit testing, setting, and clearing functions if you pass a pointer to data whose byte order is fixed. Used in this way, these functions behave the same on both architectures. For more information, see the ToolUtils.h header file in the Core Services framework and Mathematical and Logical Utilities Reference . CPU Subtype Don't try to build a binary for a specific CPU subtype. Since the CPU subtype for Intel-based Macintosh computers is generic, you can't use it to check for specific functionality. If your application requires information about specific CPU functionality, use the sysctlbyname function, providing an appropriate selector. See Mac OS X Man Pages for information on using sysctlbyname. Guidelines for Specific Scenarios Bit Shifting Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 47Dashboard Widgets Dashboard widgetstypically contain platform-independent elementssuch as HTML,JavaScript, CSS, and image files. If you create a widget that contains only these elements, it should work on both PowerPC and Intel-based Macintosh computers without any modification on your part. However, if your widget contains a plug-in, you must build the plug-in as a universal binary for it to run natively on an Intel-based Macintosh computer. For more information, see Dashboard Programming Topics. Deprecated Functions Many deprecated functions, such as those that use PICT + PS data, have byte swapping issues. You may want to replace deprecated functions at the same time you prepare your code to run as a universal binary. You’ll not only solve byte swapping issues, but your code will use functions that ultimately benefit future development. A function that is deprecated has an availability statement in its header file that states the version of Mac OS X in which the function is deprecated. Many API reference documents provide a list of deprecated functions. In addition, compiler warnings for deprecated functions are on by default in Xcode 2.2 and later. Disk Partitions The standard disk partition format on an Intel-based Macintosh computer differsfrom the disk partition format of a PowerPC-based Macintosh computer. If your application depends on the partitioning details of the disk, it may not behave as expected. Partitioning details can affect tools that examine the hard disk at a low level. By default, internal hard drives on Intel-based Macintosh computers use the GUID Partition Table (GPT)scheme and external drives use the Apple Partition Map (APM) partition scheme. To create an external USB or FireWire disk that can boot an Intel-based Macintosh computer,select the GPT disk partition scheme option using Apple Disk Utility. Starting up an Intel-based Macintosh using an APM disk is not supported. Double-Precision Values: Bit-by-Bit Sensitivity Although both architectures are IEEE 754 compliant, there are differences in the rounding procedure used by each when operating on double-precision numbers. If your application is sensitive to bit-by-bit values in double-precision numbers, be aware that the same computation performed on each architecture may produce a different numerical result. Guidelines for Specific Scenarios Dashboard Widgets Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 48For more information, see Volume 1 of the Intel developer software manuals, available from the following website: http://developer.intel.com/design/Pentium4/documentation.htm Finder Information and Low-Level File System Operations If your code operates on the file system at a low level and handles Finder information, keep in mind that the file system does not swap bytes for the following information: ● The finderInfo field in the HFSPlus data structures HFSCatalogFolder, HFSPlusCatalogFolder, HFSCatalogFile, HFSPlusCatalogFile, and HFSPlusVolumeHeader. ● The FSPermissionInfo data structure, which is used when the constant kFSCatInfoPermissions is passed to the HFSPlus functions FSGetCatalogInfo and FSGetCatalogInfoBulk. The value of multibyte fields on disk always uses big-endian format. When running on a little-endian system, you must swap the bytes of any multibyte fields. The getattrlist function retrieves the metadata associated with a file. The getxattr function, added in Mac OS X v10.4, retrieves extended attributes—those that are an extension of the basic set of attributes. When using the getxattr function to access the legacy attribute "com.apple.FinderInfo", note that as with getattrlist, the information returned by this call is not byte swapped. (For more information on the getxattr and getattrlist functions see Mac OS X Man Pages.) Note: This issue pertains only to code that operates below CarbonCore. Calls to Carbon functions such as FSGetCatalogInfo are not affected. FireWire Device Access The FireWire bus uses big-endian format. If you are developing a universal binary version of an application that accesses a FireWire device, see “FireWire Device Access on an Intel-Based Macintosh” in FireWire Device Interface Guide for a discussion of the issues you can encounter. Guidelines for Specific Scenarios Finder Information and Low-Level File System Operations Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 49Font-Related Resources Font-related resource types (FOND, NFNT, sfnt, and so forth) are in big-endian format on both PowerPC and Intel-based Macintosh computers. If your application accesses font-related resource types directly, you must swap the fields of font-related resource types yourself. The following functionsfrom the ATS for Fonts API obtain font resourcesthat are returned in big-endian format: ● ATSFontGetTableDirectory ● ATSFontGetTable ● ATSFontGetFontFamilyResource The following functions from the Font Manager API obtain font resources that are returned in big-endian format. Note that Font Manager API is based on QuickDraw technology, which was deprecated in Mac OS X v10.4. ● FMGetFontTableDirectory ● FMGetFontTable ● FMGetFontFamilyResource GWorlds When the QuickDraw function NewGWorld allocates storage for the pixel buffer, and the depth parameter is 16 or 32 bits, the byte ordering within each pixel matters. The pixelFormat field of the PixMap data structure can have the values k16BE555PixelFormat or k16LE555PixelFormat for 2-byte pixels, and k32ARGBPixelFormat or k32BGRAPixelFormat for 4-byte pixels. (These constants are defined in the Quickdraw.h header file.) By default, NewGWorld always creates big-endian pixel formats (k16BE555PixelFormat or k32ARGBPixelFormat), regardless of the endian format of the system. For best performance, it is generally preferable for you to use a pixel format that corresponds to the native byte ordering of the system. When you pass kNativeEndianPixMap in the flags parameter to NewGWorld, the byte ordering of the pixel format is big-endian on big-endian systems, and little-endian on little-endian systems. Guidelines for Specific Scenarios Font-Related Resources Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 50Note: QuickDraw does not support little-endian pixel formats on big-endian systems. You can use the GWorld pixel storage as input to the Quartz function CGBitmapContextCreate or as a data provider for the Quartz function CGImageCreate. The byte ordering of the source pixel format needs to be communicated to Quartz through additional flags in the bitmapInfo parameter. These flags are defined in the CGImage.h header file. Assuming that your bitmapInfo parameter is already set up, you now need to combine it (by using a bitwise OR operator) with kCGBitmapByteOrder16Host or kCGBitmapByteOrder32Host if you created the GWorld with a kNativeEndianPixMap flag. Similarly, you should use kCGBitmapByteOrder16Big or kCGBitmapByteOrder32Big when you know that your pixel byte order is big-endian. Java Applications Pure Java applications do not require any code changes to run on Intel-based Macintosh computers. However, Java applications that interface with PowerPC-based native code will not run successfully using Rosetta on Intel-based Macintosh computers. Specifically, the following must be built as universal binaries: ● JNI libraries built for PowerPC-based Macintosh computers are not loaded using Rosetta because the Java Virtual Machine has already launched without using Rosetta.Java applicationsfail on Intel-based Macintosh computers when trying to load PowerPC-only binaries. ● Native applications that use the VM Invocation Interface to start a Java Virtual Machine must be built as universal binaries to run on Intel-based Macintosh computers. The Java VM must run natively; attempts by an application running using Rosetta to instantiate a JVM fail. Formoreinformation,seeTechnicalQ&AQA1295:JavaonIntel-basedMacintoshComputers intheADCReference Library. Java I/O API (NIO) The I/O API (NIO) that was introduced in JDK 1.4 allows the use of native memory buffers. If you are a Java programmer who uses this API, you may need to revise your code. NIO byte buffers have a byte ordering that by default is big-endian. If you have Java code originally written for Mac OS X on PowerPC, when you create java.nio.ByteBuffers you should call the function ByteBuffer.order(ByteOrder.nativeOrder()) to set the byte order of the buffers to the native byte order for the current architecture. If you fail to do this, you will obtain flipped data when you read multibyte data from the buffer using JNI. Guidelines for Specific Scenarios Java Applications Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 51Machine Location Data Structure The Memory Management Utilities data type MachineLocation containsinformation about the geographical location of a computer. The ReadLocation and WriteLocation functions use the geographic location record to read and store the geographic location and time zone information in extended parameter RAM. If your code uses the MachineLocation data structure, you need to change it to use the MachineLocation.u.dls.Delta field that was added to the structure in Mac OS X version 10.0. To be endian-safe, change code that uses the old field: MachineLocation.u.dlsDelta = 1; to use the new field: MachineLocation.u.dls.Delta = 1; The gmtDelta field remains the same—the low 24 bits are used. The order of assignment is important. The following is incorrect because it overwrites results: MachineLocation.u.dls.Delta = 0xAA; // u = 0xAAGGGGGG; G=Garbage MachineLocation.u.gmtDelta = 0xBBBBBB; // u = 0x00BBBBBB; This is the correct way to assign the values: MachineLocation.u.gmtDelta = 0xBBBBBB; // u = 0x00BBBBB; MachineLocation.u.dls.Delta = 0xAA; // u = 0xAABBBBBB; For more details see Memory Management Utilities Reference . Mach Processes: The Task for PID Function The task_for_pid function returns the task associated with a process ID (PID). This function can be called only if the process is owned by the procmod group or if the caller is root. Guidelines for Specific Scenarios Machine Location Data Structure Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 52Metrowerks PowerPlant You can use PowerPlant on an Intel-based Macintosh computer by downloading the PowerPlant framework available from http://sourceforge.net/projects/open-powerplant. This Open Source version of the PowerPlant Framework for Mac OS X includes support for Intel and GCC 4.0. Multithreading Multithreading is a technique used to improve performance and enhance the perceived responsiveness of applications. On computers with one processor, this technique can allow a program to execute multiple pieces of code independently . On computers with more than one processor, multithreading can allow a program to execute multiple pieces of code simultaneously . If your application is single-threaded, consider threading your application to take advantage of hardware multithreading processor capabilities. If your application is multithreaded, you’ll want to ensure that the number of threads is not hard coded to a fixed number of processors. Dual-core technology improves performance by providing two physical cores within a single physical processor package. Multiprocessor and dual-core technology all exploit thread-level parallelism to improve application and system responsiveness and to boost processor throughput. When you prepare code to run as a universal binary, the multithreading capabilities of the microprocessor are transparent to you. This is true whether your application is threaded or not. However, you can optimize your code to take advantage of the specific way hardware multithreading is implemented for each architecture. Objective-C: Messages to nil In Objective-C, it is valid to send a message to a nil object. The Objective-C runtime assumes that the return value of a message sent to a nil object is nil, as long as the message returns an object or any integer scalar of size less than or equal to sizeof(void*). On Intel-based Macintosh computers, messages to a nil object always return 0.0 for methods whose return type is float, double, long double, or long long. Methods whose return value is a struct, as defined by the Mac OS X ABI Function Call Guide to be returned in registers, will return 0.0 for every field in the data structure. Other struct data types will not be filled with zeros. This is also true under Rosetta. On PowerPC Macintosh computers, the behavior is undefined. Guidelines for Specific Scenarios Metrowerks PowerPlant Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 53Objective-C Runtime: Sending Messages The information in this section is only for developers who use the Objective-C runtime library, which is used primarily for developing bridge layers between Objective-C and other languages, or for low-level debugging. Most developers do not need to use the Objective-C runtime library directly when programming in Objective-C. If your application directly callsthe Objective-C runtime function objc_msgSend_stret, you need to change your code to have it work correctly on an Intel-based Macintosh. The x86 ABI for struct-return functions differs from the ABI for struct-address-as-first-parameter functions, but the two ABIs are identical on PowerPC. When you call objc_msgSend_stret, you must cast the function to a function pointer type that uses the expected struct return type. The same applies for calls to objc_msgSendSuper_stret. For other details on the ABI, see “32-Bit Application Binary Interface” (page 84). If your application directly calls the Objective-C runtime function objc_msgSend, you should always cast to the appropriate return value. For instance, for a method that returns a BOOL data type, the following code executes properly on a PPC Macintosh but might not on an Intel-based Macintosh computer: BOOL isEqual = objc_msgSend(string, @selector("isEqual:"), otherString); To ensure that the code does executes properly on an Intel-based Macintosh computer, you would change the code to the following: BOOL isEqual = ((BOOL (*)(id, SEL, id))objc_msgSend)(object, @selector("isEqual:"), otherString); Open Firmware Macintosh computers that use an Intel microprocessor do not use Open Firmware. Although many parts of the I/O registry are present and work as expected, information that is provided by Open Firmware on a PowerPC Macintosh (such as a complete device tree) is not available in the I/O registry on a Macintosh that uses an Intel microprocessor. You can obtain some of the information from IODeviceTree by using the sysctlbyname or sysctl commands. Guidelines for Specific Scenarios Objective-C Runtime: Sending Messages Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 54OpenGL When defining an OpenGL image or texture, you need to provide a type thatspecifiesto OpenGL which format the texture is in. Most of these functions (for example, glTexImage2D) take format and type_ parameters that specify how the texture is laid out on disk or in memory. OpenGL supports a number of different image types; some are endian-neutral but others are not. Note: The advice in this section is for applications that can not reorder their pixel data because of the type of image loaders they are using. For example, a common image format is GL_RGBA with a type of GL_UNSIGNED_BYTE. This means that the image has a byte that specifies the red color data followed by a byte that specifies the green color data, and so forth. Thisformat is not endian-specific; the bytes are in the same order on all architectures. Another common image format is GL_BGRA, often specified by the type GL_UNSIGNED_INT_8_8_8_8_REV. This type means that every 4 bytes of image data are interpreted as an unsigned int, with the most significant 8 bits representing the alpha data, the next most significant 8 bits representing the red color data, and so forth. Because this format is specific to the integer format of the host, the format is interpreted differently on little-endian systemsthan on big-endian systems. When using GL_UNSIGNED_INT_8_8_8_8_REV, the OpenGL implementation expects to find data in byte order ARGB on big-endian systems, but BGRA on little-endian systems. Because there is no explicit way in OpenGL to specify a byte order of ARGB with 32-bit or 16-bit packed pixels (which are common image formats on Macintosh PowerPC computers), many applications specify GL_BGRA with GL_UNSIGNED_INT_8_8_8_8_REV. This practice works on a big-endian system such as PowerPC, but the format is interpreted differently on a little-endian system and causes images to be rendered with incorrect colors. Applications that have this problem are those that use the OpenGL host-order format types, but assume that the data referred to is always big-endian. These types include, but are not limited to the following: GL_SHORT GL_UNSIGNED_SHORT GL_INT GL_UNSIGNED_INT GL_FLOAT GL_DOUBLE GL_UNSIGNED_BYTE_3_3_2 GL_UNSIGNED_SHORT_4_4_4_4 GL_UNSIGNED_SHORT_5_5_5_1 Guidelines for Specific Scenarios OpenGL Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 55GL_UNSIGNED_INT_8_8_8_8 GL_UNSIGNED_INT_10_10_10_2 GL_UNSIGNED_SHORT_5_6_5 GL_UNSIGNED_BYTE_2_3_3_REV GL_UNSIGNED_SHORT_5_6_5_REV GL_UNSIGNED_SHORT_4_4_4_4_REV GL_UNSIGNED_SHORT_1_5_5_5_REV GL_UNSIGNED_INT_8_8_8_8_REV GL_UNSIGNED_INT_2_10_10_10_REV If your application does not use any of these types, it is unlikely to have any problems with OpenGL. Note that an application is not necessarily incorrect to use one of these types. Many applications might already present host-order data tagged with one of these formats, especially with existing cross-platform code, because the Mac OS X implementation behaves the same way as a Windows implementation. If an application incorrectly uses one of these types, its OpenGL textures and images are rendered with incorrect colors. For example, red might appear green, or the image might appear to be tinted purple. You can fix this problem in one of the following ways: 1. If the images are generated or loaded algorithmically, change the code to generate the texturesin host-order format that matches what OpenGL expects. For example, a JPEG decoder can be modified to store its output in 32-bit integers instead of four 8-bit bytes. The resulting data is identical on big-endian systems, but on a little-endian system, the bytes are in a different order. This matches the OpenGL expectation, and the existing OpenGL code continues to work on both architectures. This is the preferred approach. In many cases, rewriting the algorithms may prove a significant amount of work to implement and debug. If that’s the case, an approach that asks OpenGL to interpret the texture data differently might be a better approach for you to take. 2. If the application uses GL_UNSIGNED_INT_8_8_8_8_REV or GL_UNSIGNED_INT_8_8_8_8, it can switch between them based on the architecture. Since these two types are exactly byte swapped versions of the same format, using GL_UNSIGNED_INT_8_8_8_8_REV on a big-endian system is equivalent to using GL_UNSIGNED_INT_8_8_8_8 on a little-endian system and vice versa. Code might look as follows: glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_BGRA_EXT, #if __BIG_ENDIAN__ GL_UNSIGNED_INT_8_8_8_8_REV, #else Guidelines for Specific Scenarios OpenGL Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 56GL_UNSIGNED_INT_8_8_8_8, #endif data); If this is a common idiom, it might be easiest to define it as a macro that can be used multiple times: #if __BIG_ENDIAN__ #define ARGB_IMAGE_TYPE GL_UNSIGNED_INT_8_8_8_8_REV #else #define ARGB_IMAGE_TYPE GL_UNSIGNED_INT_8_8_8_8 #endif /* later on, use it like this */ glTexImage2D (GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_BGRA_EXT, ARGB_IMAGE_TYPE, data); Note that switching between GL_UNSIGNED_INT_8_8_8_8_REV and GL_UNSIGNED_INT_8_8_8_8 works only for this particular 32-bit packed-pixel data type. For 16-bit ARGB data stored using GL_UNSIGNED_SHORT_1_5_5_5_REV, there is no corresponding byte swapped type. Keep in mind that GL_UNSIGNED_SHORT_5_5_5_1 is not a replacement for GL_UNSIGNED_SHORT_1_5_5_5_REV on an Intel-based Macintosh computer. The format isinterpreted as bit-order arrrrrbbbbbggggg on a big-endian system, and as bit order ggrrrrrabbbbbggg on a little-endian system. 3. If you can’t use the previous approaches, you should either generate/load your data in the native endian format of the systemand use the same pixel type on both architectures or use the GL_UNPACK_SWAP_BYTES pixel store setting to instruct OpenGL to swap the bytes of any texture loaded on a little-endian system. This setting applies to all texture or image calls made with the current OpenGL context, so it needs to be set only once per OpenGL context, for example: #if __LITTLE_ENDIAN__ glPixelStorei(GL_UNPACK_SWAP_BYTES, 1); #endif This method causes images that use the problematic formats to be loaded as they would be on PowerPC. You should consider this option only if no other option is available. Enabling this option causes OpenGL to use a slower rendering path than normal. Performance-sensitiveOpenGL applications may be significantly Guidelines for Specific Scenarios OpenGL Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 57slower with this option enabled than with it off. Although this method can get an OpenGL-based program up and running in as little time as possible, it is highly recommended that you use one of the other two methods. Note: Using the GL_UNSIGNED_INT_8_8_8_8 format for GL_BGRA data is not necessarily faster than using GL_UNPACK_SWAP_BYTES. In some cases, performance decreases for rendering textures that use either of those two methods compared to using a data type such as GL_UNSIGNED_INT_8_8_8_8_REV. It’s advisable that you use Shark or other tools to analyze the performance of your OpenGL code and make sure that you are not encountering particularly bad cases. OSAtomic Functions The kernel extension functions OSDequeueAtomic and OSEnqueueAtomic are not available on an Intel-based Macintosh. For more information on these functions, see Kernel Framework Reference . Pixel Data Applications that store pixel data in memory using ARGB format must take care in how they read data. If the code is not written correctly, it’s possible to misread the data; the result is colors or alpha that appear wrong. If you see colors that appear wrong when your application runs on an Intel-based Macintosh computer, the following strategy may help you identify where pixel data is being read incorrectly. Create a test image whose pixel data is easy to identify. For example, set each pixel so that alpha is ff, red is aa, green is bb, and blue is cc. Then read that image into your application. Figure 4-1 shows such an image. Figure 4-1 A test image that can help locate the source of color problems It's also helpful to go through your code and cast pixel data to the unsigned char data type. Guidelines for Specific Scenarios OSAtomic Functions Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 58Start with the portion of your code that reads the image. Use the following GDB command to examine the pixel data as hexadecimal bytes: x/xb

This command prints the specified number of bytes, starting with the first byte of the first pixel. You should easily be able to see whether what’s displayed onscreen matches the values of the pixels in the test image. If the values you see do not match the test image, then you've identified the misreading problem. If the values match, then you need to identify other portions of your code that modify or transform pixel data, and inspect the pixel data after each transformation. PostScript Printing If you are using the Carbon Printing Manager, note that the PICT with PostScript ('pictwps') printing path is not available on Intel-based Macintosh computers except under Rosetta. If you need only to support EPS data you can use Quartz drawing together with the function PMCGImageCreateWithEPSDataProvider to allow the inclusion of EPS data as part of your Quartz drawing. If you need to generate the PostScript code for your application drawing you should use the function PMPrinterPrintWithFile. Quartz Bitmap Data The Quartz constants shown in Table 4-1 specify the byte ordering of pixel formats. These constants, which are defined in the CGImage.h header file, are used in the bitmapInfo parameter. To specify byte ordering to Quartz, use a bitwise OR operator to combine the appropriate constant with the bitmapInfo parameter. Table 4-1 Quartz constants that specify byte ordering Constant Specifies kCGBitmapByteOrderMask The byte order mask kCGBitmapByteOrder16Big 16-bit, big-endian format kCGBitmapByteOrder32Big 32-bit, big-endian format kCGBitmapByteOrder16Little 16-bit, little-endian format kCGBitmapByteOrder32Little 32-bit, little-endian format kCGBitmapByteOrder16Host 16-bit, host-endian format kCGBitmapByteOrder32Host 32-bit, host-endian format Guidelines for Specific Scenarios PostScript Printing Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 59QuickDraw Routines If you have existing code that directly accesses the picFrame field of the QuickDraw Picture data structure, you should use the QuickDraw function QDGetPictureBounds to get the appropriately swapped bounds for a Picture. This function is available in Mac OS X version 10.3 and later. Its prototype is as follows: Rect * QDGetPictureBounds( PicHandle picH, Rect *outRect) If you have existing code that uses the QuickDraw DeltaPoint function or the HIToolbox PinRect function (defined in MacWindows.h), make sure that you do not cast the function result to a Point data structure. The horizontal difference is returned in the low 16 bits, and the vertical difference is returned in the high 16 bits. You can obtain the horizontal and vertical values by using code similar to the following: Point pointDiff; SInt32 difference = DeltaPoint (p1, p2); pointDiff.h = LoWord (difference); pointDiff.v = HiWord (difference); Tip: The best solution is to convert your QuickDraw code to Quartz 2D. QuickDraw was deprecated starting in Mac OS X v10.4. For help with converting to Quartz 2D, see Quartz Programming Guide for QuickDraw Developers. QuickTime Components The Component Manager recognizes which architectures are supported by a component by looking at the 'thng' resource for the component, not the architecture of the file. You must specify the appropriate architectures in the 'thng' resource. To accomplish this, in the .r file where you define the 'thng' resource, modify your ComponentPlatformInfo array to look similar to the following: #if defined(__ppc__) kMyComponentFlags, kMyCodeType, kMyCodeID, platformPowerPCNativeEntryPoint, #endif #if defined(__i386__) kMyComponentFlags, kMyCodeType, kMyCodeID, platformIA32NativeEntryPoint, Guidelines for Specific Scenarios QuickDraw Routines Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 60#endif Then, rebuild your component. For details, see “Building a Universal Binary” (page 11). QuickTime Metadata Functions When you call the function QTMetaDataGetItemProperty and the type of the key whose value you are retrieving is code, the data returned is an OSType, not a buffer of four characters. (You can determine the key type by calling the function QTMetaDataGetItemPropertyInfo.) To ensure that your code runs properly on both PowerPC and Intel-based Macintosh computers, you must use a correctly-typed buffer so that the endian format of the data returned to you is correct. If you supply a buffer of the wrong type, for example a buffer of UInt8 instead of a buffer of OSType, the endian format of the data returned in the buffer will be wrong on Intel-based Macintosh Computers. Runtime Code Generation If your application generates code at runtime, keep in mind that the compiler assumes that the stack must be 16-byte aligned when calling into Mac OS X libraries or frameworks. 16-byte stack alignment is enforced on Intel-based Macintosh computers, which means that you need to ensure that your code is 16-byte aligned to avoid having your application crash. For more information, see Mac OS X ABI Function Call Guide . Spotlight Importers A Spotlight importer is a plug-in bundle that extracts information from files created by an application. The Spotlight engine uses importers to gather information about new and existing files. Spotlight importers are not compatible with Rosetta. To run an importer on an Intel-based Macintosh as well as on a PowerPC-based Macintosh, you must compile it as a universal binary. For more information on Spotlight, see Spotlight Overview andSpotlight Importer Programming Guide . Guidelines for Specific Scenarios QuickTime Metadata Functions Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 61System-Specific Predefined Macros The C preprocessor hasseveral predefined macros whose purpose isto indicate the type ofsystem and machine in use. If your code uses system-specific predefined macros, evaluate whether you really need to use them. In most cases applications need to know the capabilities available on a computer and not the specific system or machine on which the application is running. For example, if your application needs to know whether it is running on a little-endian or big-endian microprocessor, you should use the __BIG_ENDIAN__ or __LITTLE_ENDIAN__ macros or the Core Foundation function CFByteOrderGetCurrent. Do not use the __i386__ and __ppc__ macros for this purpose. See GNU C 4.0 Preprocessor User Guide for additional information. USB Device Access USB uses little-endian format. If you are developing a universal binary version of an application that accesses a USB device,see “USB Device Accessin an Intel-Based Macintosh”in USBDevice Interface Guide for a discussion of the issues you may encounter. See Also In addition to the following resources, check the ADC website periodically for updates and technical notes that might address other specific situations: ● Quartz Programming Guide for QuickDraw Developers which provides information on moving code from the deprecated QuickDraw API to Quartz ● IA-32 Intel Architecture Optimization Reference Manual , available from: http://developer.intel.com/design/pentium4/manuals/index_new.htm Guidelines for Specific Scenarios System-Specific Predefined Macros Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 62This chapter is relevant only for those developers who want to start writing vector-based code or whose applications already directly use the AltiVec extension to the PowerPC instruction set. AltiVec instructions, because they are processor specific, must be replaced on Intel-based Macintosh computers. You can choose from these two options: ● Use the Accelerate framework. This is the recommended option because the framework provides a layer of abstraction that lets you perform vector-based operations without needing to use low-level vector instructions yourself. See “Accelerate Framework” (page 63). ● Port AltiVec code to the Intel instruction set architecture (ISA). This solution is available for developers who have performance needs that can’t be met by using the Accelerate framework. See “Rewriting AltiVec Instructions” (page 64). Accelerate Framework The Accelerate framework, introduced in Mac OS X v10.3 and expanded in v10.4, is a set of high-performance vector-accelerated libraries. You don’t need to be concerned with the architecture of the target machine because the routines in this framework abstract the low-level details. The system automatically invokes the appropriate instruction set for the architecture that your code runs on. This framework contains the following libraries: ● vImage is the Apple image processing framework that includes high-level functions for image manipulation—convolutions, geometric transformations, histogram operations, morphological transformations, and alpha compositing—as well as utility functions that convert formats and perform other operations. See vImage Programming Guide . ● vDSP provides mathematical functions that perform digital signal processing (DSP) for applications such asspeech,sound, audio, and video processing, diagnostic medical imaging, radarsignal processing,seismic analysis, and scientific data processing. The vDSP functions operate on real and complex data types and include data type conversions, fast Fourier transforms (FFTs), and vector-to-vector and vector-to-scalar operations. ● vMathLib contains vector-accelerated versions of all routines in the standard math library. See vecLib Framework Reference . Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 63 Preparing Vector-Based Code● LAPACK is a linear algebra package that solves simultaneous sets of linear equations, tackles eigenvalue and singular solution problems, and determines least-squares solutions for linear systems. ● BLAS (Basic Linear Algebra Subroutines) performs basic vector and matrix computations. ● vForce contains routines that take matrices as input and output arguments, rather than single variables. Rewriting AltiVec Instructions Most of the tasksrequired to vectorize for AltiVec—restructuring data structures, designing parallel algorithms, eliminating branches, and so forth— are the same as those you’d need to perform for the Intel architecture. If you already have AltiVec code, you’ve already completed the fundamental vectorization work needed to rewrite your application for the Intel architecture. In many casesthe translation process will be smooth, involving direct or nearly direct substitution of AltiVec intrinsics with Intel equivalents. The MMX, SSE, SSE2, and SSE3 extensions provide analogous functionality to AltiVec. Like the AltiVec unit, these extensions are fixed-sized SIMD (Single Instruction Multiple Data) vector units, capable of a high degree of parallelism. Just as for AltiVec, code that is written to use the Intel ISA typically performs many times faster than scalar code. Before you start rewriting AltiVec instructionsfor the Intel instruction set architecture, read AltiVec/SSE Migration Guide . It outlines the key differences between architectures in terms of vector-based programming, gives an overview of the SIMD extensions on x86, lists what you need to do to build your code, and provides an in-depth discussion on alignment and other relevant issues. See Also The following resources are relevant for rewriting AltiVec instructions for the Intel architecture: ● “Architecture-Independent Vector-Based Code” (page 76) shows how to write a fast matrix-multiplication function with a minimum of architecture-specific coding. ● Intel software manuals describe the x86 vector extensions: http://developer.intel.com/design/Pentium4/documentation.htm ● Perf-Optimization-dev is a list for discussions on analyzing and optimizing performance in Mac OS X. You can subscribe at: http://lists.apple.com/mailman/listinfo/perfoptimization-devlists.apple.com Preparing Vector-Based Code Rewriting AltiVec Instructions Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 64Rosetta is a translation process that runs a PowerPC binary on an Intel-based Macintosh computer—it allows applications to run as nonnative binaries. Many, but not all, applications can run translated. Applications that run translated will never run as fast as they run as a native binary because the translation process itself incurs a processing cost. How compatible your application is with Rosetta depends on the type of application it is. An application such as a word processor that has a lot of user interaction and low computational needs is quite compatible. An application that requires a moderate amount of user interaction and has some high computational needs or that uses OpenGL is most likely also quite compatible. One that has intense computing needs isn’t compatible. Thisincludes applicationsthat need to repeatedly compute fast Fourier transforms(FFTs), that compute complex models for 3-D modeling, or that compute ray tracing. To the user, Rosetta istransparent. Unlike Classic, when the user launches an application, there aren’t any visual cues to indicate that the application is translated. The user may perceive that the application is slow to start up or that the performance is slower than it is on a PowerPC-based Macintosh. The user can discover whether an application has only a PowerPC binary by looking at the Finder information for the application. (See “Determining Whether a Binary Is Universal” (page 18).) This appendix discusses the sorts of applications that can run translated, describes how Rosetta works, points out special considerations for translated applications, shows how to force an application to run translated using Rosetta, describes how to programmatically detect whether an application is running nonnatively, and provides troubleshooting information if your application won’t run translated but you think that it should. What Can Be Translated? Rosetta is designed to translate currently shipping applicationsthat run on a PowerPC with a G3 or G4 processor and that are built for Mac OS X. That includes CFM as well as Mach-O PowerPC applications. Rosetta does not run the following: ● Applications built for any version of the Mac OS earlier than Mac OS X —that means Mac OS 9, Mac OS 8, Mac OS 7, and so forth ● The Classic environment ● Screen savers written for the PowerPC architecture Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 65 Rosetta● Code that inserts preferences in the System Preferences pane ● Applications that require a G5 processor ● Applications that depend on one or more PowerPC-only kernel extensions ● Kernel extensions ● Java applications with JNI libraries ● Java applets in applications that Rosetta can translate; that means a web browser that Rosetta can run translated will not be able to load Java applets. Rosetta does not support precise exceptions. Any application that relies on register states being accurate in exception handlers or signal handlers will not function properly running with Rosetta. For more information on the limitations of Java applications using Rosetta, see “Java Applications” (page 51) and Technical Q &A QA1295, Java on Intel-based Macintosh Computers, which is in the ADC Reference Library. How It Works When an application launches on an Intel-based Macintosh computer, the kernel detects whether the application has a native binary. If the binary is not native, the kernel launches the binary using Rosetta. If the application is one of those that can be translated, it launches and runs, although not as fast as it would as a native binary. Behind the scenes, Rosetta translates and executes the PowerPC binary code. Rosetta runs in the same thread of control as the application. When Rosetta starts an application, it translates a block of application code and executes that block. As Rosetta encounters a call to a routine that it has not yet translated, it translatesthe needed routine and continuesthe execution. The result is a smooth and continual transitioning between translation and execution. In essence, Rosetta and your application work together in a kind of symbiotic relationship. Rosetta optimizes translated code to deliver the best possible performance on the nonnative architecture. It uses a large translation buffer, and it caches code for reuse. Code that getsreused repeatedly in your application benefits the most because it needs to be translated only once. The system uses the cached translation, which is faster than translating the code again. Special Considerations Rosetta must run the entire process when it translates. This hasimplicationsfor applicationsthat use third-party plug-ins or any other component that must be loaded at the time your application launches. All parts (application, plug-ins, or other components needed at launch time) must run either nonnatively or natively. Rosetta How It Works Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 66For example, if your application is built as a universal binary, but it uses a plug-in that has only a PowerPC binary, then your application needs to run nonnatively on an Intel-based Macintosh computer to use the nonnative plug in. Rosetta takes endian issuesinto account when it translates your application. Multibyte data that moves between your application and any system processis automatically handled for you—you don’t need to concern yourself with the endian format of the data. The following kinds of multibyte data can have endian issues if the data moves between: ● Your translated application and a native process that’s not a system process ● A custom pasteboard provided by your translated application and a custom pasteboard provided by a native application ● Data files or caches provided by your translated application and a native application You might encounter thisscenario while developing a universal binary. For example, if you’ve created a universal binary for a server processthat your application relies on, and then test that process by running your application as a PowerPC binary, the endian format of the data passed from the server to your application would be wrong. You encounter the same problem if you create a universal binary for your application, but have not yet done so for a server process needed by the application. Structures that the system defines and that are written using system routines will work correctly. But consider the code in Listing A-1. Listing A-1 A structure whose endian format depends on the architecture typedef struct { int x; int y; } data_t void savefile(data_t data, int filehandle) { write(filehandle, &data, sizeof(data)); } Rosetta Special Considerations Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 67When run using Rosetta, the application will write a big-endian structure; x and y are both written as big-endian integers. When the application runs natively on an Intel-based Macintosh, it will write out a little-endian structure; x and y are written as little-endian integers. It is up to you to define data formats on disk to be of a canonical endian format. Endian-specific data formats are fine as long as any application that reads or write the data understands what the endian format of the data is and treats the data appropriately. Keep in mind that private frameworks and plug-ins can also encounter these sorts of endian issues. If a private framework creates a cache or data file, and the framework is a universal binary, then it will try to access the cache from both native and PPC processes. The framework either needs to account for the endian format of the cache when reading or writing data or needs to have two separate caches. Forcing an Application to Run Translated Assuming that the application meetsthe criteria described in “What Can Be Translated?” (page 65), applications that have only a PowerPC binary automatically run as translated on an Intel-based Macintosh. For testing purposes, there are several ways that you can force applications that have a universal binary to launch as a PowerPC binary on an Intel-based Macintosh: ● For applications, “Make a Setting in the Info Window” (page 69) ● For command-line tools “Use Terminal” (page 69) ● For an application that you are writing, “Modify the Property List” (page 69) ● Programmatically, “Use the sysctlbyname Function” (page 70) Each of these methods is described in this section. Rosetta Forcing an Application to Run Translated Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 68Make a Setting in the Info Window You can manually set which binary to execute on an Intel-based Macintosh computer by selecting the “Open using Rosetta” option in the Info window of the application. To set the option, click the application icon, then press Command-I to open the Info window. Make the setting, as shown in Figure A-1. Figure A-1 The Info window for the Calculator application Use Terminal You can force a command-line tool to run translated by entering the following in Terminal: ditto -arch ppc /tmp/toolname /tmp/toolname Modify the Property List You can set the default setting for the “Open using Rosetta” option by adding the following key to the Info.plist of your application bundle: Rosetta Forcing an Application to Run Translated Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 69LSPrefersPPC This key informs the system that the application should launch as a PowerPC binary and causes the “Open using Rosetta” checkbox to be selected. You might find this useful if you ship an application that has plug-ins that are not native at the time of shipping. Use the sysctlbyname Function The exec_affinity routine in Listing A-2 controls the preferred CPU type for sublaunched processes. You might find this routine useful if you are using fork and exec to launch applications from your application. The routine calls the sysctlbyname function with the "sysctl.proc_exec_affinity" string, passing a constant that specifies the CPU type. Pass CPU_TYPE_POWERPC to launch the PPC executable in a universal binary. (For information on sysctlbyname see Mac OS X Man Pages.) Listing A-2 A routine that controls the preferred CPU type for sublaunched processes cpu_type_t exec_affinity (cpu_type_t new_cputype) { cpu_type_t ret; cpu_type_t *newp = NULL; size_t sz = sizeof (cpu_type_t); if (new_cputype != 0) newp = &new_cputype; if (sysctlbyname("sysctl.proc_exec_affinity", &ret, &sz, newp, newp ? sizeof(cpu_type_t) : 0) == -1) { fprintf(stderr, "exec_affinity: sysctlbyname failed: %s\n", strerror(errno)); return -1; } return ret; } Rosetta Forcing an Application to Run Translated Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 70Preventing an Application from Opening Using Rosetta To prevent an application from opening using Rosetta, add the following key to the Info.plist: LSRequiresNativeExecution Programmatically Detecting a Translated Application Some developers may want to determine programmatically whether an application is running using Rosetta. For example, a developer writing device interface code may need to determine whether the user client is using the same endian format as the kernel. Listing A-3 is a utility routine that can call the sysctlbyname function on a process ID (pid). If you pass a process ID of 0 to the routine, it performs the call on the current process. Otherwise it performs the call on the processspecified by the pid value that you pass. (For information on sysctlbyname see MacOS XMan Pages.) Listing A-3 A utility routine for calling the sysctlbyname function static int sysctlbyname_with_pid (const char *name, pid_t pid, void *oldp, size_t *oldlenp, void *newp, size_t newlen) { if (pid == 0) { if (sysctlbyname(name, oldp, oldlenp, newp, newlen) == -1) { fprintf(stderr, "sysctlbyname_with_pid(0): sysctlbyname failed:" "%s\n", strerror(errno)); return -1; } } else { int mib[CTL_MAXNAME+1]; size_t len = CTL_MAXNAME; if (sysctlnametomib(name, mib, &len) == -1) { fprintf(stderr, "sysctlbyname_with_pid: sysctlnametomib failed:" "%s\n", strerror(errno)); return -1; } Rosetta Preventing an Application from Opening Using Rosetta Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 71mib[len] = pid; len++; if (sysctl(mib, len, oldp, oldlenp, newp, newlen) == -1) { fprintf(stderr, "sysctlbyname_with_pid: sysctl failed:" "%s\n", strerror(errno)); return -1; } } return 0; } The is_pid_native routine shown in Listing A-4 (page 72) calls the sysctlbyname_with_pid routine, passing the string "sysctl.proc_native". The is_pid_native routine determines whether the specified process is running natively or translated. The routine returns: ● 0 if the process is running translated using Rosetta ● 1 if the process is running natively on a PowerPC- or Intel-based Macintosh ● –1 if an unexpected error occurs Listing A-4 A routine that determines whether a process is running natively or translated int is_pid_native (pid_t pid) { int ret = 0; size_t sz = sizeof(ret); if (sysctlbyname_with_pid("sysctl.proc_native", pid, &ret, &sz, NULL, 0) == -1) { if (errno == ENOENT) { return 1; } fprintf(stderr, "is_pid_native: sysctlbyname_with_pid failed:" "%s\n", strerror(errno)); return -1; } Rosetta Programmatically Detecting a Translated Application Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 72return ret; } Note: On Mac OS X v10.4, the proc_native call fails if the current user doesn't own the process being checked. Troubleshooting If you are convinced that your application falls into the category of those that should be able to run using Rosetta but it doesn’t run or it has unexpected behavior, you can follow the procedure in this section to debug your application. This procedure works only for PowerPC binaries—not for a universal binary—and is the only way you can debug a PowerPC binary on an Intel-based Macintosh. Xcode debugging does not work for translated applications. To debug a PowerPC binary on an Intel-based Macintosh, follow these steps: 1. Open Terminal. 2. Enter the following two lines: For tcsh: setenv OAH_GDB YES //.app/Contents/MacOS/ For bash: export OAH_GDB=YES //.app/Contents/MacOS/ Rosetta Troubleshooting Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 73You’ll see the Rosetta process launch and wait for a port connection (Figure A-2). Figure A-2 Rosetta listens for a port connection 3. Open a second terminal window and start up GDB with the following command: gdb --oah Using GDB on an Intel-based Macintosh computer is just like using GDB on a PowerPC Macintosh. 4. Attach your application. attach 5. Press Tab. GDB automatically appends the process ID (pid) to your application name. 6. Press Return. 7. Type c to execute your application. Important: Do not type run. Typing run will not execute your code. It will leave your application in a state that requires you to start over from the first step. Figure A-3 shows the commands for initiating a debugging session for a PowerPC binary. After you start the session, you can debug in much the same way as you would debug a native process except that you can’t call functions—either explicitly or implicitly—from within GDB. For example, you can’t inspect CF objects by calling CFShow. Rosetta Troubleshooting Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 74Keep in mind that symbol files aren’t loaded at the start of the debugging session. They are loaded after your application is up and running. This means that any breakpoints you set are “pending breakpoints” until the executable and libraries are loaded. Figure A-3 Terminal windows with the commands for debugging a PowerPC binary on an Intel-based Macintosh computer Note: Debugging Rosetta applications from within either CodeWarrior or Xcode is not supported. Rosetta Troubleshooting Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 75The intention of this appendix isto show how to factor a mathematical calculation into architecture-independent and architecture-specific parts. Using matrix multiplication as an example, you’ll see how to write a function that works for both the PowerPC and the x86 architectures with a minimum of architecture-specific coding. You can then apply this approach to other, more complex mathematical calculations. The following basic operations are available on both architectures: ● Vector loads and stores ● Multiplication ● Addition ● An instruction to splat a float across a vector For other types of calculations, you may need to write separate versions of code. Because of the differences in the number of registers and the pipeline depths between the two architectures, it is often advantageous to provide separate versions. Note: There is a function for 4x4 matrix multiplication in the Accelerate framework (vecLib) that is tuned for both architectures. You can also call sgemm from Basic Linear Algebra Subprograms (BLAS) (also available in the Accelerate framework) to operate on larger matrices. Architecture-Specific Code Listing B-1 (page 77)showsthe architecture-specific code you need to support matrix multiplication. The code calls the architecture-independent function MyMatrixMultiply, which is shown in Listing B-2 (page 82). The code shown in Listing B-1 works properly for both instruction set architectures only if you build the code as a universal binary. For more information, see “Building a Universal Binary” (page 11). Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 76 Architecture-Independent Vector-Based CodeNote: The sample code makes use of a GCC extension to return a result from a code block ({}). The code may not compile correctly on other compilers. The extension is necessary because you cannot pass immediate values to an inline function, meaning that you must use a macro. Listing B-1 Architecture-specific code needed to support matrix multiplication #include #include #include // For each vector architecture... #if defined( __VEC__ ) // AltiVec // Set up a vector type for a float[4] array for each vector type typedef vector float vFloat; // Define some macros to map a virtual SIMD language to // each actual SIMD language. For matrix multiplication, the tasks // you need to perform are essentially the same between the two // instruction set architectures (ISA). #define vSplat( v, i ) ({ vFloat z = vec_splat( v, i ); /* return */ z; }) #define vMADD vec_madd #define vLoad( ptr ) vec_ld( 0, ptr ) #define vStore( v, ptr ) vec_st( v, 0, ptr ) #define vZero() (vector float) vec_splat_u32(0) #elif defined( __SSE__ ) // SSE // The header file xmmintrin.h defines C functions for using // SSE and SSE2 according to the Intel C programming interface #include // Set up a vector type for a float[4] array for each vector type typedef __m128 vFloat; Architecture-Independent Vector-Based Code Architecture-Specific Code Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 77// Also define some macros to map a virtual SIMD language to // each actual SIMD language. // Note that because i MUST be an immediate, it is incorrect here // to alias i to a stack based copy and replicate that 4 times. #define vSplat( v, i )({ __m128 a = v; a = _mm_shuffle_ps( a, a, \ _MM_SHUFFLE(i,i,i,i) ); /* return */ a; }) inline __m128 vMADD( __m128 a, __m128 b, __m128 c ) { return _mm_add_ps( c, _mm_mul_ps( a, b ) ); } #define vLoad( ptr ) _mm_load_ps( (float*) (ptr) ) #define vStore( v, ptr ) _mm_store_ps( (float*) (ptr), v ) #define vZero() _mm_setzero_ps() #else // Scalar #warning To compile vector code, you must specify -faltivec, -msse, or both- faltivec and -msse #warning Compiling for scalar code. // Some scalar equivalents to show what the above vector // versions accomplish // A vector, declared as a struct with 4 scalars typedef struct { float a; float b; float c; float d; }vFloat; // Splat element i across the whole vector and return it Architecture-Independent Vector-Based Code Architecture-Specific Code Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 78#define vSplat( v, i ) ({ vFloat z; z.a = z.b = z.c = z.d = ((float*) &v)[i]; /* return */ z; }) // Perform a fused-multiply-add operation on architectures that support it // result = X * Y + Z inline vFloat vMADD( vFloat X, vFloat Y, vFloat Z ) { vFloat result; result.a = X.a * Y.a + Z.a; result.b = X.b * Y.b + Z.b; result.c = X.c * Y.c + Z.c; result.d = X.d * Y.d + Z.d; return result; } // Return a vector that starts at the given address #define vLoad( ptr ) ( (vFloat*) ptr )[0] // Write a vector to the given address #define vStore( v, ptr ) ( (vFloat*) ptr )[0] = v // Return a vector full of zeros #define vZero() ({ vFloat z; z.a = z.b = z.c = z. d = 0.0f; /* return */ z; }) #endif // Prototype for a vector matrix multiply function void MyMatrixMultiply( vFloat A[4], vFloat B[4], vFloat C[4] ); int main( void ) { // The vFloat type (defined previously) is a vector or scalar array Architecture-Independent Vector-Based Code Architecture-Specific Code Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 79// that contains 4 floats // Thus each one of these is a 4x4 matrix, stored in the C storage order. vFloat A[4]; vFloat B[4]; vFloat C1[4]; vFloat C2[4]; int i, j, k; // Pointers to the elements in A, B, C1 and C2 float *a = (float*) &A; float *b = (float*) &B; float *c1 = (float*) &C1; float *c2 = (float*) &C2; // Initialize the data for( i = 0; i < 16; i++ ) { a[i] = (double) (rand() - RAND_MAX/2) / (double) (RAND_MAX ); b[i] = (double) (rand() - RAND_MAX/2) / (double) (RAND_MAX ); c1[i] = c2[i] = 0.0; } // Perform the brute-force version of matrix multiplication // and use this later to check for correctness printf( "Doing simple matrix multiply...\n" ); for( i = 0; i < 4; i++ ) for( j = 0; j < 4; j++ ) { float result = 0.0f; for( k = 0; k < 4; k++ ) result += a[ i * 4 + k] * b[ k * 4 + j ]; c1[ i * 4 + j ] = result; Architecture-Independent Vector-Based Code Architecture-Specific Code Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 80} // The vector version printf( "Doing vector matrix multiply...\n" ); MyMatrixMultiply( A, B, C2 ); // Make sure that the results are correct // Allow for some rounding error here printf( "Verifying results..." ); for( i = 0 ; i < 16; i++ ) if( fabs( c1[i] - c2[i] ) > 1e-6 ) printf( "failed at %i,%i: %8.17g %8.17g\n", i/4, i&3, c1[i], c2[i] ); printf( "done.\n" ); return 0; } The 4x4 matrix multiplication algorithm shown in Listing B-2 (page 82) is a simple matrix multiplication algorithm performed with four columns in parallel. The basic calculation is as follows: C[i][j] = sum( A[i][k] * B[k][j], k = 0... width of A ) It can be rewritten in mathematical vector notation for rows of C as the following: C[i][] = sum( A[i][k] * B[k][], k = 0... width of A ) Where: C[i][] is the ith row of C A[i][k] is the element of A at row i and column k B[k][] is the k th row of B An example calculation for C[0][] is as follows: C[0][] = A[0][0] * B[0][] + A[0][1] * B[1][] + A[0][2] * B[2][] + A[0][3] * B[3][] Architecture-Independent Vector-Based Code Architecture-Specific Code Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 81This calculation is simply a multiplication of a scalar times a vector, followed by addition of similar elements between two vectors, repeated four times, to get a vector that contains four sums of products. Performing the calculation in this way saves you from transposing B to obtain the B columns, and also saves you from adding across vectors, which is inefficient. All operations occur between similar elements of two different vectors. Architecture-Independent Matrix Multiplication Listing B-2 (page 82) shows architecture-independent vector code that performs matrix multiplication. This code compiles as scalar if you do not set up the appropriate compiler flags for PowerPC (-faltivec) or x86 (-msse), or if AltiVec is unavailable on the PowerPC. The matrices used in the MyMatrixMultply function assume the C storage order for 2D arrays, not the FORTRAN storage order. Listing B-2 Architecture-independent code that performs matrix multiplication void MyMatrixMultiply( vFloat A[4], vFloat B[4], vFloat C[4] ) { vFloat A1 = vLoad( A ); //Row 1 of A vFloat A2 = vLoad( A + 1 ); //Row 2 of A vFloat A3 = vLoad( A + 2 ); //Row 3 of A vFloat A4 = vLoad( A + 3); //Row 4 of A vFloat C1 = vZero(); //Row 1 of C, initialized to zero vFloat C2 = vZero(); //Row 2 of C, initialized to zero vFloat C3 = vZero(); //Row 3 of C, initialized to zero vFloat C4 = vZero(); //Row 4 of C, initialized to zero vFloat B1 = vLoad( B ); //Row 1 of B vFloat B2 = vLoad( B + 1 ); //Row 2 of B vFloat B3 = vLoad( B + 2 ); //Row 3 of B vFloat B4 = vLoad( B + 3); //Row 4 of B //Multiply the first row of B by the first column of A (do not sum across) C1 = vMADD( vSplat( A1, 0 ), B1, C1 ); C2 = vMADD( vSplat( A2, 0 ), B1, C2 ); C3 = vMADD( vSplat( A3, 0 ), B1, C3 ); C4 = vMADD( vSplat( A4, 0 ), B1, C4 ); Architecture-Independent Vector-Based Code Architecture-Independent Matrix Multiplication Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 82// Multiply the second row of B by the second column of A and // add to the previous result (do not sum across) C1 = vMADD( vSplat( A1, 1 ), B2, C1 ); C2 = vMADD( vSplat( A2, 1 ), B2, C2 ); C3 = vMADD( vSplat( A3, 1 ), B2, C3 ); C4 = vMADD( vSplat( A4, 1 ), B2, C4 ); // Multiply the third row of B by the third column of A and // add to the previous result (do not sum across) C1 = vMADD( vSplat( A1, 2 ), B3, C1 ); C2 = vMADD( vSplat( A2, 2 ), B3, C2 ); C3 = vMADD( vSplat( A3, 2 ), B3, C3 ); C4 = vMADD( vSplat( A4, 2 ), B3, C4 ); // Multiply the fourth row of B by the fourth column of A and // add to the previous result (do not sum across) C1 = vMADD( vSplat( A1, 3 ), B4, C1 ); C2 = vMADD( vSplat( A2, 3 ), B4, C2 ); C3 = vMADD( vSplat( A3, 3 ), B4, C3 ); C4 = vMADD( vSplat( A4, 3 ), B4, C4 ); // Write out the result to the destination vStore( C1, C ); vStore( C2, C + 1 ); vStore( C3, C + 2 ); vStore( C4, C + 3 ); } Architecture-Independent Vector-Based Code Architecture-Independent Matrix Multiplication Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 83Mac OS X ABI Function Call Guide describes the function-calling conventions used in all the architectures supported by Mac OS X. For detailed information about the IA-32 ABI, read the section “IA-32 Function Calling Conventions,” which: ● Lists data types, sizes, and natural alignment ● Describes stack structure ● Discusses prologs and epilogs ● Provides details on how arguments are passed and results are returned ● Tells which registers preserve their value after a procedure call and which ones are volatile Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 84 32-Bit Application Binary InterfaceFor information on the Apple x86-64 ABI, see: ● Mac OS X ABI Function Call Guide ● Mac OS X ABI Mach-O File Format Reference ● Mach-O Programming Topics Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 85 64-Bit Application Binary InterfaceThis table describes the changes to Universal Binary Programming Guidelines, Second Edition . Date Notes 2009-02-04 Made minor content additions. Updated “Programmatically Detecting a Translated Application ” (page 71) with details about the behavior of the sysctl call when working with the proc_native variable. 2007-02-26 Updated for Mac OS X v10.5. Removed the Appendix “Using PowerPlant” because an Open Source version that supports Intel-based Macintosh computers is available. See “Metrowerks PowerPlant” (page 53). Replaced the content in “64-Bit Application Binary Interface” (page 85) with cross-referencesto documentsthat are more thorough at describing the ABI. 2007-01-08 Added information on 64-bit and made technical corrections. Added “64-Bit Application Binary Interface” (page 85). Added a note to “OpenGL” (page 55). Revised the explanation of the return values for the code in Listing A-4 (page 72). Removed the code example in “Archived Bit Fields” (page 46) because it was incorrect. 2006-07-24 Made a few minor technical corrections. Revised “Network-Related Data” (page 34). Clarified how Listing A-4 (page 72) works. Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 86 Document Revision HistoryDate Notes 2006-06-28 Fixed link. Added “PostScript Printing” (page 59). Redirected link from Kernel Extensions Reference to Kernel Framework Reference . 2006-05-23 Removed outdated links and made a few other minor changes. Revised code regarding flippers to use an explicit UInt16 pointer and to assign back to dataptr the advanced countPtr. Updated instructions in “Troubleshooting” (page 73). Added information about the CCSResourcesFileMapped flag to “using PowerPlant”. Removed links to documentation that is no longer relevant. Added a note to “LStream.h” concerning reading and writing bool values. 2006-04-04 Corrected two function names. Revised information in “32-Bit Application Binary Interface” (page 84) so that it now only provides a link to the primary ABI reference. 2006-03-08 Improved wording and added information on Spotlight importers. Added information to “Objective-C Runtime: Sending Messages” and “Objective-C: Messages to nil.” 2006-02-07 Improved the wording in several sections. Revised wording in “Bit Shifting” (page 47), “Bit Test, Set, and Clear Functions: Carbon and POSIX” (page 47), “Troubleshooting” (page 73), and “Guidelines for Swapping Bytes” (page 28). Revised code in Listing A-4 (page 72) by adding a statement to handle versions of Mac OS that pre-date Rosetta. 2006-01-10 Updated content for Mac OS X v10.4.4. Removed the note about preliminary documentation from “Introduction to Universal Binary Programming Guidelines” (page 8). Document Revision History Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 87Date Notes Changed Xcode 2.1 to Xcode 2.2 in various places throughout the document because this is the recommended version for building a universal binary. Updated screenshots. Updated information in “Disk Partitions” (page 48), “Finder Information and Low-Level File System Operations” (page 49), “Multithreading” (page 53), “Objective-C: Messages to nil” (page 53), “QuickTime Components” (page 60), “Runtime Code Generation” (page 61), and “Values in an Array” (page 38). Added the sections “Code on the Stack: Disabling Execution” (page 22), “Extensible Firmware Interface (EFI)” (page 24), and “Mach Processes: The Task for PID Function” (page 52). In “Rosetta” (page 65), updated the sections “What Can Be Translated?” (page 65) and “Forcing an Application to Run Translated” (page 68). In “Rosetta” (page 65), added the section “Programmatically Detecting a Translated Application ” (page 71). 2005-12-06 Made refinements to existing content. Added code that shows how to swap bytes for values in an array. See “Values in an Array” (page 38). Added “Automator Scripts” (page 46), “Dashboard Widgets” (page 48), and “QuickTime Metadata Functions” (page 61). Updated for Xcode 2.2; includes pointers to newly revised tools documentation as well as improved guidelines and tips. 2005-11-09 Revised “Building Your Code” (page 12). Added “Debugging” (page 16). Added information to “Pixel Data ” (page 58) on how to track down color problems. Added the section “Quartz Bitmap Data” (page 59). Document Revision History Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 88Date Notes Added information about IP addresses and other “false” numerical values. In several places throughout the book, added cross references to newly revised, relevant documentation. Added clarification on the long double data type. See “Data Types” (page 23). Added information about using the PinRect function. See “QuickDraw Routines” (page 60). Added information about the need for Xcode targets to be native. See “Build Assumptions” (page 11) and “Building Your Code” (page 12). Corrected information about how ATS for Fonts handles font resources. See “Font-Related Resources” (page 50). Changed extended markup language to extensible markup language. Improved the grammar in “Objective-C: Messages to nil” (page 53). Fixed a link to information on Hyper-Threading Technology. See the “See Also” (page 62) section in “Guidelines for Specific Scenarios” (page 46). Made numerous editorial changes throughout. 2005-10-04 Made technical improvements and minor editorial changes throughout. Added a few resources to See Also in “Building a Universal Binary” (page 11). Changed the title of the Appendix Fast Matrix Multiplication to “Architecture-Independent Vector-Based Code” (page 76). Added new sections to the chapter “Guidelines for Specific Scenarios” (page 46). See “FireWire Device Access” (page 49) and “USB Device Access” (page 62). Added information about a relevant technical note to “QuickTime Components” (page 60). Added an example of a color issue to “Troubleshooting Your Built Application” (page 16). Revised the section “Objective-C: Messages to nil” (page 53). Document Revision History Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 89Date Notes Revised the code for swapping floating-point values. See “Floating-Point Values” (page 32). Add a reference to Cross-Development Programming Guide in the chapter “Building a Universal Binary” (page 11). Made corrections to the section “OpenGL” (page 55). 2005-09-08 Updated a substantial amount of task and conceptual information. Completely replaced information related to PowerPlant. Removed most of the content from “Preparing Vector-Based Code” (page 63) because the document AltiVec/SSE Migration Guide provides a more complete discussion of porting AltiVec code to SSE. Removed most of the content from the appendix titled Application Binary Interface becausethedocumentMacOSXABIFunctionCallGuide provides a more complete description of the IA-32 ABI for Intel-based Macintosh computers. Added a section—“Java Applications” (page 51)—that provides information about Java on Intel-based Macintosh computers, including what happens under Rosetta. Added cross-references to a technical note on this topic to “Rosetta” (page 65). 2005-08-11 Numerous minor technical and editorial changes throughout. Removed the appendix titled x86 Equivalent Instructions for AltiVec Instructions.” Made numerousminortechnical refinements and fixed a few typographical errors. 2005-07-07 Fixed typographical and linking errors. Made several improvements to technical content. 2005-06-17 New document that describes the architectural differences between PowerPC and Intel and providestipsfor writing code that can run on both. 2005-06-07 Document Revision History Retired Document | 2009-02-04 | © 2005, 2009 Apple Inc. All Rights Reserved. 90Apple Inc. © 2005, 2009 Apple Inc. All rights reserved. No part of this publication may be reproduced, stored in a retrievalsystem, or transmitted, in any form or by any means, mechanical, electronic, photocopying, recording, or otherwise, without prior written permission of Apple Inc., with the following exceptions: Any person is hereby authorized to store documentation on a single computer for personal use only and to print copies of documentation for personal use provided that the documentation contains Apple’s copyright notice. No licenses, express or implied, are granted with respect to any of the technology described in this document. Apple retains all intellectual property rights associated with the technology described in this document. This document is intended to assist application developers to develop applications only for Apple-labeled computers. Apple Inc. 1 Infinite Loop Cupertino, CA 95014 408-996-1010 Apple, the Apple logo, AppleScript, Carbon, Cocoa, ColorSync, eMac, Finder, FireWire, Logic, Mac, MacOS, Macintosh,Objective-C,OS X, Pages, Panther, Quartz, QuickDraw, QuickTime, Rosetta, Spotlight, and Xcode are trademarks of Apple Inc., registered in the U.S. and other countries. Intel and Intel Core are registered trademarks of Intel Corporation or its subsidiaries in the United States and other countries. Java is a registered trademark of Oracle and/or its affiliates. MMX is a trademark of Intel Corporation or its subsidiaries in the United States and other countries. OpenGL is a registered trademark of Silicon Graphics, Inc. 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Object-Oriented Programming with Objective-CContents Introduction 5 Who Should Read This Document 5 Organization of This Document 6 See Also 6 Why Objective-C? 7 Object-Oriented Programming 8 Data and Operations 8 Interface and Implementation 9 The Object Model 12 The Messaging Metaphor 13 Classes 15 Modularity 16 Reusability 16 Mechanisms of Abstraction 18 Encapsulation 18 Polymorphism 19 Inheritance 20 Class Hierarchies 21 Subclass Definitions 21 Uses of Inheritance 22 Dynamism 23 Dynamic Typing 24 Dynamic Binding 25 Dynamic Loading 27 Structuring Programs 29 Outlet Connections 29 Extrinsic and Intrinsic Connections 30 Activating the Object Network 31 Aggregation and Decomposition 31 Models and Frameworks 32 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 2Structuring the Programming Task 34 Collaboration 34 Organizing Object-Oriented Projects 35 Designing on a Large Scale 35 Separating the Interface from the Implementation 35 Dividing the Work into Modules 35 Keeping the Interface Simple 36 Making Decisions Dynamically 36 Inheriting Generic Code 36 Reusing Tested Code 36 Document Revision History 38 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 3 ContentsFigures Object-Oriented Programming 8 Figure 2-1 Interface and implementation 9 The Object Model 12 Figure 3-1 An object 12 Figure 3-2 Objects in a network 13 Figure 3-3 An inheritance hierarchy 21 Structuring Programs 29 Figure 4-1 Outlets 30 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 4An object-oriented approach to application development makes programs more intuitive to design, faster to develop, more amenable to modification, and easier to understand. Most object-oriented development environments consist of at least three parts: ● A library of objects ● A set of development tools ● An object-oriented programming language and support library The Objective-C language is a programming language designed to enable sophisticated object-oriented programming. Objective-C is defined as a small but powerfulset of extensionsto the standard ANSI C language. Its additions to C are mostly based on Smalltalk, one of the first object-oriented programming languages. Objective-C is designed to give C full object-oriented programming capabilities and to do so in a simple and straightforward way. Important: This document does not describe the Objective-C language itself. To learn about the language, see The Objective-C Programming Language . Every object-oriented programming language and environment has a different perspective on what object-oriented means, how objects behave, and how programs might be structured. This document offers the Objective-C perspective. Who Should Read This Document For those who have never used object-oriented programming to create applications, this document is designed to help you become familiar with object-oriented development. It spells out some of the implications of object-oriented design and gives you a flavor of what writing an object-oriented program is really like. If you have developed applications using an object-oriented environment, this document will help you understand the fundamental concepts that are essential to understanding how to use Objective-C effectively and how to structure a program that uses Objective-C. 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 5 IntroductionBecause this isn’t a document about C, it assumes some prior acquaintance with that language. However, it doesn’t have to be an extensive acquaintance. Object-oriented programming in Objective-C is sufficiently different from procedural programming in ANSI C that you won’t be hampered if you’re not an experienced C programmer. Organization of This Document This document is divided into several chapters: ● “Why Objective-C?” (page 7) explains why Objective-C was chosen as the development language for the Cocoa frameworks. ● “Object-Oriented Programming” (page 8) discusses the rationale for object-oriented programming languages and introduces much of the terminology. It develops the ideas behind object-oriented programming techniques. Even if you’re already familiar with object-oriented programming, you are encouraged to read this chapter to gain a sense of the Objective-C perspective on object orientation and its use of terminology. ● “The Object Model” (page 12) describes how you can think of a program in terms of units that combine state and behavior—objects. It then explains how you characterize these objects as belonging to a particular class, how one class can inheritstate and behavior from another class, and how objects can send messages to other objects. ● “Structuring Programs” (page 29) explains how you think about designing an object-oriented program by creating connections between objects. It introducesthe techniques of aggregation and decomposition, which divide responsibility between differentsorts of object, and the role of frameworksin defining libraries of objects designed to work together. ● “Structuring the Programming Task” (page 34) discusses issues of project management related to collaboration among programmers and to code implementation. See Also The Objective-C Programming Language describes the Objective-C programming language. Objective-C Runtime Programming Guide describes how you can interact with the Objective-C runtime. Objective-C Runtime Reference describes the data structures and functions of the Objective-C runtime support library. Your programs can use these interfaces to interact with the Objective-C runtime system. For example, you can add classes or methods, or obtain a list of all class definitions for loaded classes. Introduction Organization of This Document 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 6The Objective-C language was chosen for a variety of reasons. First and foremost, it’s an object-oriented language. The kind of functionality that’s packaged in the Cocoa frameworks can only be delivered through object-oriented techniques. Second, because Objective-C is an extension ofstandard ANSI C, existing C programs can be adapted to use the software frameworks without losing any of the work that went into their original development. Because Objective-C incorporates C, you get all the benefits of C when working within Objective-C. You can choose when to do something in an object-oriented way (define a new class, for example) and when to stick to procedural programming techniques (define a structure and some functions instead of a class). Moreover, Objective-C is a fundamentally simple language. Its syntax is small, unambiguous, and easy to learn. Object-oriented programming, with its self-conscious terminology and emphasis on abstract design, often presents a steep learning curve to new recruits. A well-organized language like Objective-C can make becoming a proficient object-oriented programmer that much less difficult. Compared to other object-oriented languages based on C, Objective-C is very dynamic. The compiler preserves a great deal of information about the objects themselves for use at runtime. Decisions that otherwise might be made at compile time can be postponed until the program isrunning. Dynamism gives Objective-C programs unusual flexibility and power. For example, it yields two big benefits that are hard to get with other nominally object-oriented languages: ● Objective-C supports an open style of dynamic binding, a style that can accommodate a simple architecture for interactive user interfaces. Messages are not necessarily constrained by either the class of the receiver or even the method name, so a software framework can allow for user choices at runtime and permit developers freedom of expression in their design. (Terminology such as dynamic binding , message , class, and receiver are explained in due course in this document.) ● Dynamism enables the construction of sophisticated development tools. An interface to the runtime system provides access to information about running applications, so it’s possible to develop tools that monitor, intervene, and reveal the underlying structure and activity of Objective-C applications. Historical note: As a language, Objective-C has a long history. It was created at the Stepstone company in the early 1980s by Brad Cox and Tom Love. It was licensed by NeXT Computer Inc. in the late 1980s to develop the NeXTStep frameworks that preceded Cocoa. NeXT extended the language in several ways, for example, with the addition of protocols. 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 7 Why Objective-C?As humans, we’re constantly faced with myriad facts and impressions that we must make sense of. To do so, we must abstract underlying structure away from surface details and discover the fundamental relations at work. Abstractions reveal causes and effects, expose patterns and frameworks, and separate what’s important from what’s not. Object orientation provides an abstraction of the data on which you operate; moreover, it provides a concrete grouping between the data and the operations you can perform with the data—in effect giving the data behavior. Data and Operations Programming languages have traditionally divided the world into two parts—data and operations on data. Data is static and immutable, except as the operations may change it. The procedures and functions that operate on data have no lasting state of their own; they’re useful only in their ability to affect data. This division is, of course, grounded in the way computers work, so it’s not one that you can easily ignore or push aside. Like the equally pervasive distinctions between matter and energy and between nouns and verbs, it forms the background against which we work. At some point, all programmers—even object-oriented programmers—must lay out the data structures that their programs will use and define the functions that will act on the data. With a procedural programming language like C, that’s about all there is to it. The language may offer various kinds of support for organizing data and functions, but it won’t divide the world any differently. Functions and data structures are the basic elements of design. Object-oriented programming doesn’tso much dispute this view of the world asrestructure it at a higher level. It groups operations and data into modular units called objects and lets you combine objects into structured networks to form a complete program. In an object-oriented programming language, objects and object interactions are the basic elements of design. Every object has both state (data) and behavior (operations on data). In that, they’re not much different from ordinary physical objects. It’s easy to see how a mechanical device,such as a pocket watch or a piano, embodies both state and behavior. But almost anything that’s designed to do a job does, too. Even simple things with no moving parts such as an ordinary bottle combine state (how full the bottle is, whether or not it’s open, how warm its contents are) with behavior (the ability to dispense its contents at various flow rates, to be opened or closed, to withstand high or low temperatures). 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 8 Object-Oriented ProgrammingIt’sthisresemblance to real thingsthat gives objects much of their power and appeal. They can not only model components of real systems, but equally as well fulfill assigned roles as components in software systems. Interface and Implementation To invent programs, you need to be able to capture abstractions and express them in the program design. It’s the job of a programming language to help you do this. The language should facilitate the process of invention and design by letting you encode abstractions that reveal the way things work. It should let you make your ideas concrete in the code you write. Surface details shouldn’t obscure the architecture of your program. All programming languages provide devices that help express abstractions. In essence, these devices are ways of grouping implementation details, hiding them, and giving them, at least to some extent, a common interface—much as a mechanical objectseparatesitsinterface from itsimplementation, asillustrated in Figure 2-1. Figure 2-1 Interface and implementation 9 10 11 8 7 6 interface implementation Looking at such a unit from the inside, as the implementer, you’d be concerned with what it’s composed of and how it works. Looking at it from the outside, as the user, you’re concerned only with what it is and what it does. You can look past the details and think solely in terms of the role that the unit plays at a higher level. The principal units of abstraction in the C language are structures and functions. Both, in different ways, hide elements of the implementation: ● On the data side of the world, C structures group data elements into larger units that can then be handled as single entities. While some code must delve inside the structure and manipulate the fields separately, much of the program can regard it as a single thing—not as a collection of elements, but as what those elements taken together represent. One structure can include others, so a complex arrangement of information can be built from simpler layers. Object-Oriented Programming Interface and Implementation 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 9In modern C, the fields of a structure live in their own namespace—that is, their names won’t conflict with identically named data elements outside the structure. Partitioning the program namespace is essential for keeping implementation details out of the interface. Imagine, for example, the enormous task of assigning a different name to every piece of data in a large program and of making sure new names don’t conflict with old ones. ● On the proceduralside of the world, functions encapsulate behaviorsthat can be used repeatedly without being reimplemented. Data elements local to a function, like the fields within a structure, are protected within their own namespace. Because functions can reference (call) other functions, complex behaviors can be built from smaller pieces. Functions are reusable. Once defined, they can be called any number of times without again considering the implementation. The most generally useful functions can be collected in libraries and reused in many different applications. All the user needs is the function interface, not the source code. However, unlike data elements, functions aren’t partitioned into separate namespaces. Each function must have a unique name. Although the function may be reusable, its name is not. C structures and functions are able to expresssignificant abstractions, but they maintain the distinction between data and operations on data. In a procedural programming language, the highest units of abstraction still live on one side or the other of the data-versus-operations divide. The programs you design must always reflect, at the highest level, the way the computer works. Object-oriented programming languages don’t lose any of the virtues of structures and functions—they go a step further and add a unit capable of abstraction at a higher level, a unit that hides the interaction between a function and its data. Suppose, for example, that you have a group of functions that act on a particular data structure. You want to make those functions easier to use by, asfar as possible, taking the structure out of the interface. So you supply a few additional functions to manage the data. All the work of manipulating the data structure—allocating memory for it, initializing it, getting information from it, modifying values within it, keeping it up to date, and freeing its memory—is done through the functions. All the user doesis call the functions and passthe structure to them. With these changes, the structure has become an opaque token that other programmers never need to look inside. They can concentrate on what the functions do, not on how the data is organized. You’ve taken the first step toward creating an object. The nextstep isto give thisidea support in the programming language and completely hide the data structure so that it doesn’t even have to be passed between the functions. The data becomes an internal implementation detail; all that’s exported to users is a functional interface. Because objects completely encapsulate their data (hide it), users can think of them solely in terms of their behavior. Object-Oriented Programming Interface and Implementation 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 10With thisstep, the interface to the functions has become much simpler. Callers don’t need to know how they’re implemented (what data they use). It’s fair now to call this an object. The hidden data structure unites all the functions that share access to it. So an object is more than a collection of random functions; it’s a bundle of related behaviors that are supported by shared data. To use a function that belongs to an object, you first create the object (thus giving it its internal data structure), and then tell the object which function it should perform. You begin to think in terms of what the object does, rather than in terms of the individual functions. This progression from thinking about functions and data structures to thinking about object behaviors is the essence of learning object-oriented programming. It may seem unfamiliar at first, but as you gain experience with object-oriented programming, you find it’s a more natural way to think about things. Everyday programming terminology isreplete with analogiesto real-world objects of various kinds—lists, containers, tables, controllers, even managers. Implementing such things as programming objects merely extends the analogy in a natural way. A programming language can be judged by the kinds of abstractions that it enables you to encode. You shouldn’t be distracted by extraneous matters or forced to express yourself using a vocabulary that doesn’t match the reality you’re trying to capture. If, for example, you must alwaystend to the business of keeping the right data matched with the right procedure, you’re forced at all times to be aware of the entire program at a low level of implementation. While you might still invent programs at a high level of abstraction, the path from imagination to implementation can become quite tenuous—and more and more difficult as programs become bigger and more complicated. By providing another, higher level of abstraction, object-oriented programming languages give you a larger vocabulary and a richer model to program in. Object-Oriented Programming Interface and Implementation 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 11The insight of object-oriented programming isto combine state and behavior—data and operations on data—in a high-level unit, an object, and to give it language support. An object is a group of related functions and a data structure that serves those functions. The functions are known as the object’s methods, and the fields of its data structure are its instance variables. The methods wrap around the instance variables and hide them from the rest of the program, as Figure 3-1 illustrates. Figure 3-1 An object method method e m doht method data If you’ve ever tackled any kind of difficult programming problem, it’slikely that your design hasincluded groups of functions that work on a particular kind of data—implicit “objects” without the language support. Object-oriented programming makes these function groups explicit and permits you to think in terms of the group, rather than its components. The only way to an object’s data, the only interface, is through its methods. By combining both state and behavior in a single unit, an object becomes more than either alone; the whole really is greater than the sum of its parts. An object is a kind of self-sufficient “subprogram” with jurisdiction over a specific functional area. It can play a full-fledged modular role within a larger program design. Terminology: Object-oriented terminology variesfrom language to language. For example, in C++, methods are called member functions and instance variables are known as data members. This document uses the terminology of Objective-C, which has its basis in Smalltalk. For example, if you were to write a program that modeled home water usage, you might invent objects to represent the various components of the water-delivery system. One might be a Faucet object that would have methods to start and stop the flow of water, set the rate of flow, return the amount of water consumed in a given period, and so on. To do this work, a Faucet object would need instance variables to keep track of whether the tap is open or shut, how much water is being used, and where the water is coming from. 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 12 The Object ModelClearly, a programmatic Faucet object can be smarter than a real one (it’s analogous to a mechanical faucet with lots of gauges and instruments attached). But even a real faucet, like any system component, exhibits both state and behavior. To effectively model a system, you need programming units, like objects, that also combine state and behavior. A program consists of a network of interconnected objects that call upon each other to solve a part of the puzzle (as illustrated in Figure 3-2 (page 13)). Each object has a specific role to play in the overall design of the program and is able to communicate with other objects. Objects communicate through messages, which are requests to perform methods. Figure 3-2 Objects in a network data data data message The objects in the network won’t all be the same. For example, in addition to Faucet objects, the program that models water usage might also have Pipe objectsthat can deliver water to the Faucet and Valve objects to regulate the flow among pipes. There could be a Building object to coordinate a set of pipes, valves, and faucets, some Appliance objects—corresponding to dishwashers, toilets, and washing machines—that can turn valves on and off, and maybe some User objects to work the appliances and faucets. When a Building object is asked how much water is being used, it might call upon each Faucet and Valve object to report its current state. When a user starts up an appliance, the appliance will need to turn on a valve to get the water it requires. The Messaging Metaphor Every programming paradigm comes with its own terminology and metaphors. The jargon associated with object-oriented programming invites you to think about what goes on in a program from a particular perspective. The Object Model The Messaging Metaphor 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 13There’s a tendency, for example, to think of objects as actors and to endow them with human-like intentions and abilities. It’s tempting sometimes to talk about an object deciding what to do about a situation, asking other objectsfor information, introspecting about itself to get requested information, delegating responsibility to another object, or managing a process. Rather than think in terms of functions or methods doing the work, as you would in a procedural programming language, this metaphor asks you to think of objects as performing their methods. Objects are not passive containers for state and behavior, but are said to be the agents of the program’s activity. This metaphor is actually very useful. An object is like an actor in a couple of respects: It has a particular role to play within the overall design of the program, and within that role it can act fairly independently of the other parts of the program. It interacts with other objects as they play their own roles, but it is self-contained and to a certain extent can act on its own. Like an actor onstage, it can’t stray from the script, but the role it plays can be multifaceted and complex. The idea of objects as actorsfits nicely with the principal metaphor of object-oriented programming—the idea that objects communicate through messages. Instead of calling a method as you would a function, you send a message to an object requesting it to perform one of its methods. Although it can take some getting used to, this metaphor leads to a useful way of looking at methods and objects. It abstracts methods away from the particular data they act on and concentrates on behavior instead. For example, in an object-oriented programming interface, a start method might initiate an operation, an archive method might archive information, and a draw method might produce an image. Exactly which operation is initiated, which information is archived, and which image is drawn isn’t revealed by the method name. Different objects might perform these methods in different ways. Thus, methods are a vocabulary of abstract behaviors. To invoke one of those behaviors, you have to make it concrete by associating the method with an object. This is done by naming the object as the receiver of a message. The object you choose as receiver determines the exact operation that is initiated, the data that is archived, or the image that is drawn. Because methods belong to objects, they can be invoked only through a particular receiver (the owner of the method and of the data structure the method will act on). Different receivers can have different implementations of the same method. Consequently, different receivers can do different thingsin response to the same message. The result of a message can’t be calculated from the message or method name alone; it also depends on the object that receives the message. By separating the message (the requested behavior) from the receiver (the owner of a method that can respond to the request), the messaging metaphor perfectly captures the idea that behaviors can be abstracted away from their particular implementations. The Object Model The Messaging Metaphor 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 14Classes A program can have more than one object of the same kind. The program that models water usage, for example, might have several faucets and pipes and perhaps a handful of appliances and users. Objects of the same kind are said to be members of the same class. All members of a class are able to perform the same methods and have matching sets of instance variables. They also share a common definition; each kind of object is defined just once. In this, objects are similar to C structures. Declaring a structure defines a type. For example, the declaration struct key { char *word; int count; }; defines the struct key type. Once defined, the structure name can be used to produce any number of instances of the type: struct key a, b, c, d; struct key *p = malloc(sizeof(struct key) * MAXITEMS); The declaration is a template for a kind of structure, but it doesn’t create a structure that the program can use. It takes another step to allocate memory for an actual structure of that type, a step that can be repeated any number of times. Similarly, defining an object creates a template for a kind of object. It defines a class of objects. The template can be used to produce any number of similar objects—instances of the class. For example, there would be a single definition of the Faucet class. Using this definition, a program could allocate as many Faucet instances as it needed. A class definition is like a structure definition in that it lays out an arrangement of data elements (instance variables) that become part of every instance. Each instance has memory allocated for its own set of instance variables, which store values particular to the instance. However, a class definition differs from a structure declaration in that it also defines methods that specify the behavior of class members. Every instance is characterized by its access to the methods defined for the class. Two objects with equivalent data structures but different methods would not belong to the same class. The Object Model Classes 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 15Modularity To a C programmer, a module is nothing more than a file containing source code. Breaking a large (or even not-so-large) program into different files is a convenient way of splitting it into manageable pieces. Each piece can be worked on independently and compiled alone, and then integrated with other pieces when the program is linked. Using the static storage class designator to limit the scope of names to just the files where they’re declared enhances the independence of source modules. This kind of module is a unit defined by the file system. It’s a container for source code, not a logical unit of the language. What goes into the container is up to each programmer. You can use them to group logically related parts of the code, but you don’t have to. Files are like the drawers of a dresser; you can put your socks in one drawer, underwear in another, and so on, or you can use another organizing scheme or simply choose to mix everything up. Access to methods: It’s convenient to think of methods as being part of an object, just as instance variables are. As in Figure 3-1 (page 12), methods can be diagrammed as surrounding the object’s instance variables. But methods aren’t grouped with instance variables in memory. Memory is allocated for the instance variables of each new object, but there’s no need to allocate memory for methods. All an instance needs is access to its methods, and all instances of the same class share access to the same set of methods. There’s only one copy of the methods in memory, no matter how many instances of the class are created. Object-oriented programming languages support the use of file containers for source code, but they also add a logical module to the language—class definitions. As you’d expect, it’s often the case that each classis defined in its own source file—logical modules are matched to container modules. In Objective-C, for example, it would be possible to define the part of the Valve class that interacts with Pipe objects in the same file that defines the Pipe class, thus creating a container module for Pipe-related code and splitting the Valve class into more than one file. The Valve class definition would still act as a modular unit within the construction of the program—it would still be a logical module—no matter how many files the source code was located in. The mechanisms that make class definitions logical units of the language are discussed in some detail under “Mechanisms of Abstraction” (page 18). Reusability A principal goal of object-oriented programming is to make the code you write as reusable as possible—to have it serve many different situations and applications—so that you can avoid reimplementing, even if only slightly differently, something that’s already been done. The Object Model Classes 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 16Reusability is influenced by factors such as these: ● How reliable and bug-free the code is ● How clear the documentation is ● How simple and straightforward the programming interface is ● How efficiently the code performs its tasks ● How full the feature set is These factors don’t apply just to the object model. They can be used to judge the reusability of any code—standard C functions as well as class definitions. Efficient and well-documented functions, for example, would be more reusable than undocumented and unreliable ones. Nevertheless, a general comparison would show that class definitions lend themselves to reusable code in waysthat functions do not. There are variousthings you can do to make functions more reusable—for example, passing data as parameters rather than assuming specifically named global variables. Even so, it turns out that only a small subset of functions can be generalized beyond the applications they were originally designed for. Their reusability is inherently limited in at least three ways: ● Function names are global; each function must have a unique name (except for those declared static). This naming requirement makesit difficult to rely heavily on library code when building a complex system. The programming interface would be hard to learn and so extensive that it couldn’t easily capture significant generalizations. Classes, on the other hand, can share programming interfaces. When the same naming conventions are used over and over, a great deal of functionality can be packaged with a relatively small and easy-to-understand interface. ● Functions are selected from a library one at a time. It’s up to programmersto pick and choose the individual functions they need. In contrast, objects come as packages of functionality, not as individual methods and instance variables. They provide integrated services, so users of an object-oriented library won’t get bogged down piecing together their own solutions to a problem. ● Functions are typically tied to particular kinds of data structures devised for a specific program. The interaction between data and function is an unavoidable part of the interface. A function is useful only to those who agree to use the same kind of data structures it accepts as parameters. Because it hides its data, an object doesn’t have this problem. This is one of the principal reasons that classes can be reused more easily than functions. The Object Model Classes 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 17An object’s data is protected and won’t be touched by any other part of the program. Methods can therefore trust its integrity. They can be sure that external access hasn’t put data into an illogical or untenable state. As a result, an object data structure is more reliable than one passed to a function, and methods can depend on it more. Reusable methods are consequently easier to write. Moreover, because an object’s data is hidden, a class can be reimplemented to use a different data structure without affecting its interface. All programs that use the class can pick up the new version without changing any source code; no reprogramming is required. Mechanisms of Abstraction To this point, objects have been introduced as units that embody higher-level abstractions and as coherent role-players within an application. However, they couldn’t be used this way without the support of various language mechanisms. Two of the most important mechanisms are encapsulation and polymorphism. Encapsulation keeps the implementation of an object out of its interface, and polymorphism results from giving each class its own namespace. The following sections discuss each of these mechanisms in turn. Encapsulation To design effectively at any level of abstraction, you need to be able to leave details of implementation behind and think in terms of units that group those details under a common interface. For a programming unit to be truly effective, the barrier between interface and implementation must be absolute. The interface must encapsulate the implementation—that is, hide it from other parts of the program. Encapsulation protects an implementation from unintended actions and from inadvertent access. In C, a function is clearly encapsulated; its implementation is inaccessible to other parts of the program and protected from whatever actions might be taken outside the body of the function. In Objective-C, method implementations are similarly encapsulated, but more importantly so are an object’sinstance variables. They’re hidden inside the object and invisible outside it. The encapsulation of instance variables is sometimes also called information hiding . It might seem, at first, that hiding the information in instance variables might constrain your freedom as a programmer. Actually, it gives you more room to act and frees you from constraints that might otherwise be imposed. If any part of an object’s implementation could leak out and become accessible or a concern to other parts of the program, it would tie the hands both of the object’s implementer and of those who would use the object. Neither could make modifications without first checking with the other. The Object Model Mechanisms of Abstraction 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 18Suppose, for example, that you’re interested in the Faucet object being developed for the program that models water use and you want to incorporate it in another program you’re writing. Once the interface to the object is decided, you don’t have to be concerned when others work on it, fix bugs, and find better ways to implement it. You get the benefit of these improvements, but none of them affects what you do in your program. Because you depend solely on the interface, nothing they do can break your code. Your program is insulated from the object’s implementation. Moreover, although those implementing the Faucet object might be interested in how you use the class and might try to make sure it meets your needs, they don’t have to be concerned with the way you write your code. Nothing you do can touch the implementation of the object or limit their freedom to make implementation changesin future releases. The implementation isinsulated from anything that you or other users of the object might do. Polymorphism The ability of different objects to respond, each in its own way, to identical messages is called polymorphism. Polymorphism results from the fact that every class lives in its own namespace. The names assigned within a class definition don’t conflict with names assigned anywhere outside it. Thisistrue both of the instance variables in an object’s data structure and of the object’s methods: ● Just as the fields of a C structure are in a protected namespace, so are an object’s instance variables. ● Method names are also protected. Unlike the names of C functions, method names aren’t global symbols. The name of a method in one class can’t conflict with method names in other classes; two very different classes can implement identically named methods. Method names are part of an object’sinterface. When a message issent requesting that an object do something, the message names the method the object should perform. Because different objects can have methods with the same name, the meaning of a message must be understood relative to the particular object that receives the message. The same message sent to two different objects can invoke two distinct methods. The main benefit of polymorphism is that it simplifies the programming interface. It permits conventions to be established that can be reused in class after class. Instead of inventing a new name for each new function you add to a program, the same names can be reused. The programming interface can be described as a set of abstract behaviors, quite apart from the classes that implement them. The Object Model Mechanisms of Abstraction 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 19Overloading: The terms polymorphism and parameter overloading refer basically to the same thing, but from slightly different points of view. Polymorphism takes a pluralistic point of view and notesthatseveral classes can each have a method with the same name. Parameter overloading takes the point of the view of the method name and notes that it can have different effects depending on the parameters passed to it.Operator overloading issimilar. Itrefersto the ability to turn operators of the language (such as == and + in C) into methods that can be assigned particular meanings for particular kinds of objects. Objective-C implements polymorphism of method names, but not parameter or operator overloading. For example, suppose you want to report the amount of water used by an Appliance object over a given period of time. Instead of defining an amountConsumed method for the Appliance class, an amountDispensedAtFaucet method for a Faucet class, and a cumulativeUsage method for a Building class, you can simply define a waterUsed method for each class. This consolidation reduces the number of methods used for what is conceptually the same operation. Polymorphism also permits code to be isolated in the methods of different objects rather than be gathered in a single function that enumerates all the possible cases. This makes the code you write more extensible and reusable. When a new case comes along, you don’t have to reimplement existing code; you need only to add a new class with a new method, leaving the code that’s already written alone. For example, suppose you have code that sends a draw message to an object. Depending on the receiver, the message might produce one of two possible images. When you want to add a third case, you don’t have to change the message or alter existing code; you merely allow another object to be assigned as the message receiver. Inheritance The easiest way to explain something new is to start with something understood. If you want to describe what a schooner is, it helpsif your listeners already know what a sailboat is. If you want to explain how a harpsichord works, it’s best if you can assume your audience has already looked inside a piano, or has seen a guitar played, or at least is familiar with the idea of a musical instrument. The same is true if you want to define a new kind of object; the description is simpler if it can start from the definition of an existing object. With thisin mind, object-oriented programming languages permit you to base a new class definition on a class already defined. The base class is called a superclass; the new class is its subclass. The subclass definition specifies only how it differs from the superclass; everything else is taken to be the same. The Object Model Inheritance 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 20Nothing is copied from superclass to subclass. Instead, the two classes are connected so that the subclass inherits all the methods and instance variables of itssuperclass, much as you want your listener’s understanding ofschooner to inherit what they already know aboutsailboats. If the subclass definition were empty (if it didn’t define any instance variables or methods of its own), the two classes would be identical (except for their names) and would share the same definition. It would be like explaining what a fiddle is by saying that it’s exactly the same as a violin. However, the reason for declaring a subclassisn’t to generate synonyms; it to create something at least a little different from its superclass. For example, you might extend the behavior of the fiddle to allow it to play bluegrass in addition to classical music. Class Hierarchies Any class can be used as a superclass for a new class definition. A class can simultaneously be a subclass of another class, and a superclass for its own subclasses. Any number of classes can thus be linked in a hierarchy of inheritance, such as the one depicted in Figure 3-3. Figure 3-3 An inheritance hierarchy root C D E F A B Every inheritance hierarchy begins with a root class that has no superclass. From the root class, the hierarchy branches downward. Each class inherits from its superclass and, through its superclass, from all the classes above it in the hierarchy. Every class inherits from the root class. Each class is the accumulation of all the class definitions in its inheritance chain. In the example above, class D inherits both from C—itssuperclass—and the root class. Members of the D class have methods and instance variables defined in all three classes—D, C, and root. Typically, every class has just one superclass and can have an unlimited number of subclasses. However, in some object-oriented programming languages (though not in Objective-C), a class can have more than one superclass; it can inherit through multiple sources. Instead of having a single hierarchy that branches downward as shown in Figure 3-3, multiple inheritance lets some branches of the hierarchy (or of different hierarchies) merge. Subclass Definitions A subclass can make three kinds of changes to the definition it inherits through its superclass: The Object Model Inheritance 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 21● It can expand the class definition it inherits by adding new methods and instance variables. This is the most common reason for defining a subclass. Subclasses always add new methods and add new instance variables if the methods require it. ● It can modify the behavior it inherits by replacing an existing method with a new version. This is done by simply implementing a new method with the same name as one that’sinherited. The new version overrides the inherited version. (The inherited method doesn’t disappear; it’s still valid for the class that defined it and other classes that inherit it.) ● It can refine or extend the behavior it inherits by replacing an existing method with a new version, but it still retains the old version by incorporating it in the new method. A subclass sends a message to perform the old version in the body of the new method. Each class in an inheritance chain can contribute part of a method’s behavior. In Figure 3-3 (page 21), for example, class D might override a method defined in class C and incorporate C’s version, while C’s version incorporates a version defined in the root class. Subclasses thus tend to fill out a superclass definition, making it more specific and specialized. They add, and sometimesreplace, code rather than subtract it. Note that methods generally can’t be disinherited and instance variables can’t be removed or overridden. Uses of Inheritance The classic examples of an inheritance hierarchy are borrowed from animal and plant taxonomies. For example, there could be a class corresponding to the Pinaceae (pine) family of trees. Itssubclasses could be Fir, Spruce, Pine, Hemlock, Tamarack, DouglasFir, and TrueCedar, corresponding to the various genera that make up the family. The Pine class might have SoftPine and HardPine subclasses, with WhitePine, SugarPine, and BristleconePine as subclasses of SoftPine, and PonderosaPine, JackPine, MontereyPine, and RedPine as subclasses of HardPine. There’s rarely a reason to program a taxonomy like this, but the analogy is a good one. Subclasses tend to specialize a superclass or adapt it to a special purpose, much as a species specializes a genus. Here are some typical uses of inheritance: ● Reusing code. If two or more classes have some things in common but also differ in some ways, the common elements can be put in a single class definition that the other classes inherit. The common code is shared and need only be implemented once. For example, Faucet, Valve, and Pipe objects, defined for the program that models water use, all need a connection to a water source and should be able to record the rate of flow. These commonalities can be encoded once, in a class that the Faucet, Valve, and Pipe classes inherit from. A Faucet object can be said to be a kind of Valve object, so perhaps the Faucet class would inherit most of what it is from Valve, and add little of its own. The Object Model Inheritance 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 22● Setting up a protocol. A class can declare a number of methods that its subclasses are expected to implement. The class might have empty versions of the methods, or it might implement partial versions that are to be incorporated into the subclass methods. In either case, its declarations establish a protocol that all its subclasses must follow. When different classes implement similarly named methods, a program is better able to make use of polymorphism in its design. Setting up a protocol that subclasses must implement helps enforce these conventions. ● Delivering generic functionality. One implementer can define a class that contains a lot of basic, general code to solve a problem but that doesn’t fill in all the details. Other implementers can then create subclasses to adapt the generic class to their specific needs. For example, the Appliance class in the program that models water use might define a generic water-using device thatsubclasses would turn into specific kinds of appliances. Inheritance is thus both a way to make someone else’s programming task easier and a way to separate levels of implementation. ● Making slight modifications. When inheritance is used to deliver generic functionality, set up a protocol, or reuse code, a class is devised that other classes are expected to inherit from. But you can also use inheritance to modify classes that aren’t intended as superclasses. Suppose, for example, that there’s an object that would work well in your program, but you’d like to change one or two things that it does. You can make the changes in a subclass. ● Previewing possibilities. Subclasses can also be used to factor out alternatives for testing purposes. For example, if a class is to be encoded with a particular user interface, alternative interfaces can be factored into subclasses during the design phase of the project. Each alternative can then be demonstrated to potential usersto see which they prefer. When the choice is made, the selected subclass can be reintegrated into its superclass. Dynamism At one time in programming history, the question of how much memory a program might use was typically settled when the source code was compiled and linked. All the memory the program would ever need was set aside for it as it was launched. This memory was fixed; it could neither grow nor shrink. In hindsight, it’s evident what a serious constraint this was. It limited not only how programs were constructed, but what you could imagine a program doing. It constrained design, not just programming technique. The introduction of functions that dynamically allocate memory as a program runs (such as malloc) opened possibilities that didn’t exist before. The Object Model Dynamism 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 23Compile-time and link-time constraints are limiting because they force issues to be decided from information found in the programmer’s source code, rather than from information obtained from the user as the program runs. Although dynamic allocation removes one such constraint, many others, equally as limiting as static memory allocation, remain. For example, the elements that make up an application must be matched to data types at compile time. And the boundaries of an application are typically set at link time. Every part of the application must be united in a single executable file. New modules and new types can’t be introduced as the program runs. Objective-C seeks to overcome these limitations and to make programs as dynamic and fluid as possible. It shifts much of the burden of decision making from compile time and link time to runtime. The goal is to let program users decide what will happen, rather than constrain their actions artificially by the demands of the language and the needs of the compiler and linker. Three kinds of dynamism are especially important for object-oriented design: ● Dynamic typing, waiting until runtime to determine the class of an object ● Dynamic binding, determining at runtime what method to invoke ● Dynamic loading, adding new components to a program as it runs Dynamic Typing The compiler typically complains if the code you write assigns a value to a type that can’t accommodate it. You might see warnings like these: incompatible types in assignment assignment of integer from pointer lacks a cast Type checking is useful, but there are times when it can interfere with the benefits you get from polymorphism, especially if the type of every object must be known to the compiler. Suppose, for example, that you want to send an object a message to perform the start method. Like other data elements, the object isrepresented by a variable. If the variable’stype (its class) must be known at compile time, it would be impossible to let runtime factors influence the decision about what kind of object should be assigned to the variable. If the class of the variable is fixed in source code, so is the version of start that the message invokes. The Object Model Dynamism 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 24If, on the other hand, it’s possible to wait until runtime to discover the class of the variable, any kind of object could be assigned to it. Depending on the class of the receiver, the start message might invoke different versions of the method and produce very different results. Dynamic typing thus givessubstance to dynamic binding (discussed next). But it does more than that. It permits associations between objects to be determined at runtime, rather than forcing them to be encoded in a static design. For example, a message could pass an object as a parameter without declaring exactly what kind of object it is—that is, without declaring its class. The message receiver might then send its own messages to the object, again without ever caring about what kind of object it is. Because the receiver uses the passed object to do some of its work, it is in a sense customized by an object of indeterminate type (indeterminate in source code, that is, not at runtime). Dynamic Binding In standard C, you can declare a set of alternative functions, such as the standard string-comparison functions, int strcmp(const char *, const char *); /* case sensitive */ int strcasecmp(const char *, const char *); /*case insensitive*/ and declare a pointer to a function that has the same return and parameter types: int (* compare)(const char *, const char *); You can then wait until runtime to determine which function to assign to the pointer, if ( **argv == 'i' ) compare = strcasecmp; else compare = strcmp; and call the function through the pointer: if ( compare(s1, s2) ) ... Thisis akin to what in object-oriented programming is called dynamic binding, delaying the decision of exactly which method to perform until the program is running. The Object Model Dynamism 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 25Although not all object-oriented languages support it, dynamic binding can be routinely and transparently accomplished through messaging. You don’t have to go through the indirection of declaring a pointer and assigning values to it as shown in the example above. You also don’t have to assign each alternative procedure a different name. Messages invoke methods indirectly. Every message expression must find a method implementation to “call.” To find that method, the messaging machinery must check the class of the receiver and locate itsimplementation of the method named in the message. When this is done at runtime, the method is dynamically bound to the message. When it’s done by the compiler, the method is statically bound. Late binding: Some object-oriented programming languages (notably C++) require a message receiver to be statically typed in source code, but don’t require the type to be exact. An object can be typed to its own class or to any classthat it inheritsfrom. The compiler therefore can’t tell whether the message receiver is an instance of the class specified in the type declaration, an instance of a subclass, or an instance ofsome more distantly derived class. Because it doesn’t know the exact class of the receiver, it can’t know which version of the method named in the message to invoke. In this circumstance, the choice is between treating the receiver as if it were an instance of the specified class and simply bind the method defined for that class to the message, or waiting until some later time to resolve the situation. In C++, the decision is postponed to link time for methods (member functions) that are declared virtual. Thisissometimesreferred to aslate binding rather than dynamic binding . While dynamic in the sense that it happens at runtime, it carries with it strict compile-time type constraints. As discussed here (and implemented in Objective-C), dynamic binding is unconstrained. Dynamic binding is possible even in the absence of dynamic typing, but it’s not very interesting. There’s little benefit in waiting until runtime to match a method to a message when the class of the receiver is fixed and known to the compiler. The compiler could just as well find the method itself; the runtime result won’t be any different. However, if the class of the receiver is dynamically typed, there’s no way for the compiler to determine which method to invoke. The method can be found only after the class of the receiver isresolved at runtime. Dynamic typing thus entails dynamic binding. Dynamic typing also makes dynamic binding interesting, for it opensthe possibility that a message might have very different results depending on the class of the receiver. Runtime factors can influence the choice of receiver and the outcome of the message. The Object Model Dynamism 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 26Dynamic typing and binding also open the possibility that the code you write can send messages to objects not yet invented. If object types don’t have to be decided until runtime, you can give others the freedom to design their own classes and name their own data types and still have your code send messagesto their objects. All you need to agree on are the messages, not the data types. Note: Dynamic binding is routine in Objective-C. You don’t need to arrange for it specially, so your design never needs to bother with what’s being done when. Dynamic Loading Historically, in many common environments, before a program can run, all its parts had to be linked together in one file. When it was launched, the entire program was loaded into memory at once. Some object-oriented programming environments overcome this constraint and allow different parts of an executable program to be kept in different files. The program can be launched in bits and pieces as they’re needed. Each piece is dynamically loaded and linked with the rest of program as it’s launched. User actions can determine which parts of the program are in memory and which aren’t. Only the core of a large program needs to be loaded at the start. Other modules can be added as the user requests their services. Modules the user doesn’t request make no memory demands on the system. Dynamic loading raisesinteresting possibilities. For example, an entire program does not have to be developed at once. You can deliver your software in pieces and update one part of it at a time. You can devise a program that groups several tools under a single interface, and load just the tools the user wants. The program can even offer sets of alternative tools to do the same job—the user then selects one tool from the set and only that tool would be loaded. Perhaps the most important current benefit of dynamic loading is that it makes applications extensible. You can allow others to add to and customize a program you’ve designed. All your program needs to do is provide a framework that others can fill in, and, at runtime, find the pieces that they’ve implemented and load them dynamically. The main challenge that dynamic loading faces is getting a newly loaded part of a program to work with parts already running, especially when the different parts were written by different people. However, much of this problem disappears in an object-oriented environment because code is organized into logical modules with a clear division between implementation and interface. When classes are dynamically loaded, nothing in the newly loaded code can clash with the code already in place. Each class encapsulates its implementation and has an independent namespace. The Object Model Dynamism 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 27In addition, dynamic typing and dynamic binding let classes designed by othersfit effortlessly into the program you’ve designed. Once a class is dynamically loaded, it’s treated no differently than any other class. Your code can send messages to their objects and theirs to yours. Neither of you has to know what classes the other has implemented. You need only agree on a communications protocol. Loading and linking: Although it’s the term commonly used, dynamic loading could just as well be called dynamic linking . Programs are linked when their various parts are joined so that they can work together; they’re loaded when they’re read into volatile memory at launch time. Linking usually precedes loading. Dynamic loading refers to the process of separately loading new or additional parts of a program and linking them dynamically to the parts already running. The Object Model Dynamism 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 28Object-oriented programs have two kinds of structure. One can be seen in the inheritance hierarchy of class definitions. The other is evident in the pattern of message passing as the program runs. These messages reveal a network of object connections. ● The inheritance hierarchy explains how objects are related by type. For example, in the program that models water use, it might turn out that faucets and pipes are the same kind of object, except that faucets can be turned on and off and pipes can have multiple connections to other pipes. This similarity would be captured in the program design if the Faucet and Pipe classes inherit from a common superclass. ● The network of object connections explains how the program works. For example, Appliance objects might send messages requesting water to valves, and valves to pipes. Pipes might communicate with the Building object, and the Building object with all the valves, faucets, and pipes, but not directly with appliances. To communicate with each other in this way, objects must know about each other. An Appliance object would need a connection to a Valve object, and a Valve object to a Pipe object, and so on. These connections define a program structure. Object-oriented programs are designed by laying out the network of objects with their behaviors and patterns of interaction and by arranging the hierarchy of classes. There’s structure both in the program’s activity and in its definition. Outlet Connections Part of the task of designing an object-oriented program isto arrange the object network. The network doesn’t have to be static; it can change dynamically as the program runs. Relationships between objects can be improvised as needed, and the cast of objects that play assigned roles can change from time to time. But there has to be a script. Some connections can be entirely transitory. A message might contain a parameter identifying an object, perhaps the sender of the message, that the receiver can communicate with. As it responds to the message, the receiver can send messages to that object, perhaps identifying itself or still another object that the object can in turn communicate with. Such connections are fleeting; they last only as long as the chain of messages. 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 29 Structuring ProgramsBut not all connections between objects can be handled on the fly. Some need to be recorded in program data structures. There are various ways to do this. A table might be kept of object connections, or there might be a service that identifies objects by name. However, the simplest way is for each object to have instance variables that keep track of the other objects it must communicate with. These instance variables—termed outlets because they record the outlets for messages—define the principal connections between objects in the program network. Although the names of outlet instance variables are arbitrary, they generally reflect the rolesthat outlet objects play. Figure 4-1 illustrates an object with four outlets—an agent, a friend, a neighbor, and a boss. The objects that play these parts may change every now and then, but the roles remain the same. Figure 4-1 Outlets agent friend neighbor boss Some outlets are set when the object isfirst initialized and may never change. Others might be set automatically asthe consequence of other actions. Still others can be set freely, using methods provided just for that purpose. However they’re set, outlet instance variables reveal the structure of the application. They link objects into a communicating network, much as the components of a water system are linked by their physical connections or as individuals are linked by their patterns of social relations. Extrinsic and Intrinsic Connections Outlet connections can capturemany different kinds of relationships between objects. Sometimesthe connection is between objects that communicate more or less as equal partners in an application, each with its own role to play and neither dominating the other. For example, an Appliance object might have an outlet instance variable to keep track of the valve it’s connected to. Structuring Programs Outlet Connections 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 30Sometimes one object should be seen as being part of another. For example, a Faucet object might use a Meter object to measure the amount of water being released. The Meter object would serve no other object and would act only under orders from the Faucet object. It would be an intrinsic part of the Faucet object, in contrast to an Appliance object’s extrinsic connection to a Valve object. Similarly, an object that oversees other objects might keep a list of its charges. A Building object, for example, might have a list of all the Pipe objects in the program. The Pipe objects would be considered an intrinsic part of the Building object and belong to it. Pipe objects, on the other hand, would maintain extrinsic connections to each other. Intrinsic outlets behave differently from extrinsic ones. When an object is freed or archived in a file on disk, the objects that its intrinsic outlets point to must be freed or archived with it. For example, when a faucet is freed, its meter is rendered useless and therefore should be freed as well. A faucet archived without its meter would be of little use when it’s unarchived (unless it could create a new Meter object for itself). Extrinsic outlets, on the other hand, capture the organization of the program at a higher level. They record connections between relatively independent program subcomponents. When an Appliance object is freed, the Valve object it was connected to still is of use and remains in place. When an Appliance object is unarchived, it can be connected to another valve and resume playing the same sort of role it played before. Activating the Object Network The object network is set into motion by an external stimulus. If you’re writing an interactive application with a user interface, it will respond to user actions on the keyboard and mouse. A program that tries to factor very large numbers might start when you pass it a target number on the command line. Other programs might respond to data received over a phone line, information obtained from a database, or information about the state of a mechanical process the program monitors. Programs often are activated by a flow of events, which are reports of external activity ofsome sort. Applications that display a user interface are driven by events from the keyboard and mouse. Every press of a key or click of the mouse generates events that the application receives and responds to. An object-oriented program structure (a network of objects that’s prepared to respond to an external stimulus) is ideally suited for this kind of user-driven application. Aggregation and Decomposition Another part of the design task is deciding the arrangement of classes—when to add functionality to an existing class by defining a subclass and when to define an independent class. The problem can be clarified by imagining what would happen in the extreme case: Structuring Programs Aggregation and Decomposition 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 31● It’s possible to conceive of a program consisting of just one object. Because it’s the only object, it can send messages only to itself. It therefore can’t take advantage of polymorphism, or the modularity of a variety of classes, or a program design conceived as a network of interconnected objects. The true structure of the program would be hidden inside the class definition. Despite being written in an object-oriented language, there would be very little that was object-oriented about it. ● On the other hand, it’s also possible to imagine a program that consists of hundreds of different kinds of objects, each with very few methods and limited functionality. Here, too, the structure of the program would be lost, this time in a maze of object connections. Obviously, it’s best to avoid either of these extremes, to keep objects large enough to take on a substantial role in the program but small enough to keep that role well-defined. The structure of the program should be easy to grasp in the pattern of object connections. Nevertheless, the question often arises of whether to add more functionality to a class or to factor out the additional functionality and put it in a separate class definition. For example, a Faucet object needs to keep track of how much water is being used over time. To do that, you could either implement the necessary methods in the Faucet class, or you could devise a generic Meter object to do the job, as suggested earlier. Each Faucet object would have an outlet connecting it to a Meter object, and the meter would not interact with any object but the faucet. The choice often depends on your design goals. If the Meter object could be used in more than one situation, perhaps in another project entirely, it would increase the reusability of your code to factor the metering task into a separate class. If you have reason to make Faucet objects as self-contained as possible, the metering functionality could be added to the Faucet class. It’s generally better to try for reusable code and avoid having large classes that do so many things that they can’t be adapted to othersituations. When objects are designed as components, they become that much more reusable. What works in one system or configuration might well work in another. Dividing functionality between different classes doesn’t necessarily complicate the programming interface. If the Faucet class keeps the Meter object private, the Meter interface wouldn’t have to be published for users of the Faucet class; the object would be as hidden as any other Faucet instance variable. Models and Frameworks Objects combine state and behavior, and so resemble things in the real world. Because they resemble real things, designing an object-oriented program is very much like thinking about real things—what they do, how they work, and how one thing is connected to another. Structuring Programs Models and Frameworks 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 32When you design an object-oriented program, you are, in effect, putting together a computer simulation of how something works. Object networks look and behave like models of real systems. An object-oriented program can be thought of as a model, even if there’s no actual counterpart to it in the real world. Each component of the model—each kind of object—is described in terms of its behavior, responsibilities, and interactions with other components. Because an object’s interface lies in its methods, not its data, you can begin the design process by thinking about what a system component must do, not how it’s represented in data. Once the behavior of an object is decided, the appropriate data structure can be chosen, but this is a matter of implementation, not the initial design. For example, in the water-use program, you wouldn’t begin by deciding what the Faucet data structure looked like, but what you wanted a Faucet object to do—make a connection to a pipe, be turned on and off, adjust the rate of flow, and so on. The design is therefore not bound from the outset by data choices. You can decide on the behavior first and implement the data afterwards. Your choice of data structures can change over time without affecting the design. Designing an object-oriented program doesn’t necessarily entail writing great amounts of code. The reusability of class definitions means that the opportunity is great for building a program largely out of classes devised by others. It might even be possible to construct interesting programs entirely out of classes someone else defined. As the suite of class definitions grows, you have more and more reusable parts to choose from. Reusable classes come from many sources. Development projects often yield reusable class definitions, and some enterprising developers market them. Object-oriented programming environments typically come with class libraries. There are well over two hundred classes in the Cocoa libraries. Some of these classes offer basic services (hashing, data storage, remote messaging). Others are more specific (user interface devices, video displays, sound). Typically, a group of library classes work together to define a partial program structure. These classes constitute a software framework (or kit) that can be used to build a variety of different kinds of applications. When you use a framework, you accept the program model it provides and adapt your design to it. You use the framework by: ● Initializing and arranging instances of framework classes ● Defining subclasses of framework classes ● Defining new classes of your own to work with classes defined in the framework In each of these ways, you not only adapt your program to the framework, but you also adapt the generic framework structure to the specialized purposes of your application. The framework, in essence, sets up part of an object network for your program and provides part of its class hierarchy. Your own code completes the program model started by the framework. Structuring Programs Models and Frameworks 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 33Object-oriented programming not only structures programs in a better way, it also helps structure the programming task. As software tries to do more and more, and programs become bigger and more complicated, the problem of managing the task also grows. There are more pieces to fit together and more people working together to build them. The object-oriented approach offers ways of dealing with this complexity, not just in design, but also in the organization of the work. Collaboration Complex software requires an extraordinary collaborative effort among people who must be individually creative, yet still make what they do fit exactly with what others are doing. The sheer size of the effort and the number of people working on the same project at the same time in the same place can get in the way of the group’s ability to work cooperatively towards a common goal. In addition, collaboration is often impeded by barriers of time, space, and organization: ● Code must be maintained, improved, and used long after it’s written. Programmers who collaborate on a project may not be working on it at the same time, so they may not be in a position to talk things over and keep each other informed about details of the implementation. ● Even if programmers work on the same project at the same time, they may not be located in the same place. This also inhibits how closely they can work together. ● Programmers working in different groups with different priorities and different schedules often must collaborate on projects. Communication across organizational barriers isn’t always easy to achieve. The answer to these difficulties must grow out of the way programs are designed and written. It can’t be imposed from the outside in the form of hierarchical management structures and strict levels of authority. These often get in the way of people’s creativity, and become burdensin and of themselves. Rather, collaboration must be built into the work itself. 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 34 Structuring the Programming TaskThat’s where object-oriented programming techniques can help. For example, the reusability of object-oriented code means that programmers can collaborate effectively, even when they work on different projects at different times or are in different organizations, just by sharing their code in libraries. This kind of collaboration holds a great deal of promise, for it can conceivably lighten difficult tasks and make seemingly impossible projects achievable. Organizing Object-Oriented Projects Object-oriented programming helps restructure the programming task in ways that benefit collaboration. It helps eliminate the need to collaborate on low-level implementation details, while providing structures that facilitate collaboration at a higher level. Almost every feature of the object model, from the possibility of large-scale design to the increased reusability of code, has consequences for the way people work together. Designing on a Large Scale When programs are designed at a high level of abstraction, the division of labor is more easily conceived. It can match the division of the program on logical lines; the way a project is organized can grow out of its design. With an object-oriented design, it’s easier to keep common goals in sight, instead of losing them in the implementation, and easier for everyone to see how the piece they’re working on fits into the whole. Their collaborative efforts are therefore more likely to be on target. Separating the Interface from the Implementation The connections between the various components of an object-oriented program are worked out early in the design process. They can be well-defined, at least for the initial phase of development, before implementation begins. During implementation, only this interface needs to be coordinated, and most of that falls naturally out of the design. Because each class encapsulates its implementation and has its own namespace, there’s no need to coordinate implementation details. Collaboration is simpler when there are fewer coordination requirements. Dividing the Work into Modules The modularity of object-oriented programming means that the logical components of a large program can each be implemented separately. Different people can work on different classes. Each implementation task is isolated from the others. Structuring the Programming Task Organizing Object-Oriented Projects 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 35Modularity has benefits, not just for organizing the implementation, but for fixing problems later. Because implementations are contained within class boundaries, problems that come up are also likely to be isolated. It’s easier to track down bugs when they’re located in a well-defined part of the program. Separating responsibilities by class also means that each part can be worked on by specialists. Classes can be updated periodically to optimize their performance and make the best use of new technologies. These updates don’t have to be coordinated with other parts of the program. As long as the interface to an object doesn’t change, improvements to its implementation can be scheduled at any time. Keeping the Interface Simple The polymorphism of object-oriented programs yields simpler programming interfaces, since the same names and conventions can be reused in any number of classes. The result is less to learn, a greater shared understanding of how the whole system works, and a simpler path to cooperation and collaboration. Making Decisions Dynamically Because object-oriented programs make decisions dynamically at runtime, lessinformation needsto be supplied at compile time (in source code) to make two pieces of code work together. Consequently, there’s less to coordinate and less to go wrong. Inheriting Generic Code Inheritance is a way of reusing code. If you can define your classes as specializations of more generic classes, your programming task is simplified. The design is simplified as well, since the inheritance hierarchy lays out the relationships between the different levels of implementation and makes them easier to understand. Inheritance also increases the reusability and reliability of code. The code placed in a superclass is tested by its subclasses. The generic class you find in a library will have been tested by other subclasses written by other developers for other applications. Reusing Tested Code The more software you can borrow from others and incorporate in your own programs, the less you have to do yourself. There’s more software to borrow in an object-oriented programming environment because the code is more reusable. Collaboration between programmers working in different places for different organizations is enhanced, while the burden of each project is eased. Structuring the Programming Task Organizing Object-Oriented Projects 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 36Classes and frameworks from an object-oriented library can make substantial contributions to your program. When you program with the software frameworks provided by Apple, for example, you’re effectively collaborating with the programmers at Apple; you’re contracting a part of your program, often a substantial part, to them. You can concentrate on what you do best and leave other tasks to the library developer. Your projects can be prototyped faster, completed faster, with less of a collaborative challenge at your own site. The increased reusability of object-oriented code also increases its reliability. A class taken from a library is likely to have found its way into a variety of applications and situations. The more the code has been used, the more likely it is that problems will have been encountered and fixed. Bugs that would have seemed strange and hard to find in your program might already have been tracked down and eliminated. Structuring the Programming Task Organizing Object-Oriented Projects 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 37This table describes the changes to Object-Oriented Programming with Objective-C. Date Notes 2010-11-15 Edited for content and clarity. 2008-11-19 Corrected typographical errors. 2007-12-11 Corrected a typographical error. 2007-07-09 Originally published as part of "The Objective-C Programming Language". 2010-11-15 | © 2010 Apple Inc. All Rights Reserved. 38 Document Revision HistoryApple Inc. © 2010 Apple Inc. All rights reserved. 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Table View Programming Guide for iOSContents About Table Views in iOS Apps 8 At a Glance 9 Table Views Draw Their Rows Using Cells 9 Responding to Selections of Rows 9 In Editing Mode You Can Add, Delete, and Reorder Rows 10 To Create a Table View, Use a Storyboard 10 Prerequisites 11 See Also 11 Table View Styles and Accessory Views 12 Table View Styles 12 Plain Table Views 13 Grouped Table Views 15 Standard Styles for Table View Cells 17 Accessory Views 21 Overview of the Table View API 23 Table View 23 Table View Controller 23 Data Source and Delegate 23 Extension to the NSIndexPath Class 24 Table View Cells 24 Navigating a Data Hierarchy with Table Views 25 Hierarchical Data Models and Table Views 25 The Data Model as a Hierarchy of Model Objects 25 Table Views and the Data Model 26 View Controllers and Navigation-Based Apps 28 Navigation Controllers 28 Navigation Bars 29 Table View Controllers 31 Managing Table Views in a Navigation-Based App 32 Design Pattern for Navigation-Based Apps 35 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 2Creating and Configuring a Table View 36 Basics of Table View Creation 36 Recommendations for Creating and Configuring Table Views 38 Creating a Table View Using a Storyboard 38 Choose the Table View’s Display Style 39 Choose the Table View’s Content Type 40 Design the Table View’s Rows 42 Create Additional Table Views 42 Learn More by Creating a Sample App 43 Creating a Table View Programmatically 43 Adopt the Data Source and Delegate Protocols 43 Create and Configure a Table View 44 Populating a Dynamic Table View with Data 44 Populating a Static Table View With Data 46 Populating an Indexed List 47 Optional Table View Configurations 52 Add a Custom Title 52 Provide a Section Title 53 Indent a Row 53 Vary a Row’s Height 54 Customize Cells 54 A Closer Look at Table View Cells 55 Characteristics of Cell Objects 55 Using Cell Objects in Predefined Styles 57 Customizing Cells 60 Loading Table View Cells from a Storyboard 61 Programmatically Adding Subviews to a Cell’s Content View 69 Cells and Table View Performance 73 Managing Selections 74 Selections in Table Views 74 Responding to Selections 74 Programmatically Selecting and Scrolling 78 Inserting and Deleting Rows and Sections 80 Inserting and Deleting Rows in Editing Mode 81 When a Table View is Edited 81 An Example of Deleting a Table-View Row 84 An Example of Adding a Table-View Row 85 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 3 ContentsBatch Insertion, Deletion, and Reloading of Rows and Sections 87 An Example of Batched Insertion and Deletion Operations 88 Ordering of Operations and Index Paths 89 Managing the Reordering of Rows 91 What Happens When a Row is Relocated 92 Examples of Moving a Row 93 Document Revision History 95 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 4 ContentsFigures and Listings About Table Views in iOS Apps 8 Figure I-1 Table views of various kinds 8 Table View Styles and Accessory Views 12 Figure 1-1 A table view in the plain style 13 Figure 1-2 A table view configured as an indexed list 14 Figure 1-3 A table view configured as a selection list 15 Figure 1-4 A table view in the grouped style 16 Figure 1-5 Header and footer of a section 17 Figure 1-6 Default table row style 18 Figure 1-7 Table row style with a subtitle under the title 19 Figure 1-8 Table row style with a right-aligned subtitle 20 Figure 1-9 Table row style in Contacts format 21 Navigating a Data Hierarchy with Table Views 25 Figure 3-1 Mapping levels of the data model to table views 27 Figure 3-2 Navigation controller and view controllers in a navigation-based app 29 Figure 3-3 Navigation bars and common control items 30 Figure 3-4 A storyboard with two table view controllers 33 Listing 3-1 Passing data to a destination view controller 34 Listing 3-2 Passing data to a source view controller 34 Creating and Configuring a Table View 36 Figure 4-1 Calling sequence for creating and configuring a table view 37 Figure 4-2 The master view controller in the Master-Detail Application storyboard 39 Figure 4-3 A dynamic table view 40 Figure 4-4 A static table view 41 Listing 4-1 Adopting the data source and delegate protocols 43 Listing 4-2 Creating a table view 44 Listing 4-3 Populating a dynamic table view with data 45 Listing 4-4 Populating a static table view with data 46 Listing 4-5 Defining the model-object interface 48 Listing 4-6 Loading the table-view data and initializing the model objects 48 Listing 4-7 Preparing the data for the indexed list 49 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 5Listing 4-8 Providing section-index data to the table view 50 Listing 4-9 Populating the rows of an indexed list 51 Listing 4-10 Adding a title to the table view 52 Listing 4-11 Returning a title for a section 53 Listing 4-12 Custom indentation of a row 53 Listing 4-13 Varying row height 54 A Closer Look at Table View Cells 55 Figure 5-1 Parts of a table view cell 55 Figure 5-2 Parts of a table-view cell in editing mode 56 Figure 5-3 Default cell content in a UITableViewCell object 57 Figure 5-4 A table view with rows showing both images and text 58 Figure 5-5 Table view cells in a storyboard 61 Figure 5-6 Table view rows drawn with a custom prototype cell 62 Figure 5-7 Table view rows drawn with multiple cells 66 Figure 5-8 Making connections to your static cell content 68 Figure 5-9 Cells with custom content as subviews 70 Listing 5-1 Configuring a UITableViewCell object with both image and text 58 Listing 5-2 Alternating the background color of cells 60 Listing 5-3 Adding data to a cell using tags 63 Listing 5-4 Adding data to a cell using outlets 65 Listing 5-5 Defining outlet properties for static cell objects 66 Listing 5-6 Setting the data in the user interface 68 Listing 5-7 Adding subviews to a cell’s content view 70 Managing Selections 74 Listing 6-1 Responding to a row selection 75 Listing 6-2 Setting a switch object as an accessory view and responding to its action message 75 Listing 6-3 Managing a selection list—exclusive list 77 Listing 6-4 Managing a selection list—inclusive list 77 Listing 6-5 Programmatically selecting a row 78 Inserting and Deleting Rows and Sections 80 Figure 7-1 Calling sequence for inserting or deleting rows in a table view 82 Figure 7-2 Deletion of section and row and insertion of row 90 Listing 7-1 View controller responding to setEditing:animated: 84 Listing 7-2 Customizing the editing style of rows 84 Listing 7-3 Updating the data-model array and deleting the row 85 Listing 7-4 Adding an Add button to the navigation bar 85 Listing 7-5 Responding to a tap on the Add button 86 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 6 Figures and ListingsListing 7-6 Adding the new item to the data-model array 86 Listing 7-7 Batch insertion and deletion methods 87 Listing 7-8 Inserting and deleting a block of rows in a table view 88 Managing the Reordering of Rows 91 Figure 8-1 Reordering a row 91 Figure 8-2 Calling sequence for reordering a row in a table view 92 Listing 8-1 Excluding a row from relocation 93 Listing 8-2 Updating the data-model array for the relocated row 94 Listing 8-3 Retargeting the destination row of a move operation 94 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 7 Figures and ListingsTable views are versatile user interface objects frequently found in iOS apps. A table view presents data in a scrollable list of multiple rows that may be divided into sections. Table views have many purposes: ● To let users navigate through hierarchically structured data ● To present an indexed list of items ● To display detail information and controls in visually distinct groupings ● To present a selectable list of options Figure I-1 Table views of various kinds A table view has only one column and allows vertical scrolling only. It consists of rows in sections. Each section can have a header and a footer that displaystext or an image. However, many table views have only one section with no visible header or footer. Programmatically, the UIKit framework identifies rows and sections through their index number: Sections are numbered 0 through n – 1 from the top of a table view to the bottom; rows are numbered 0 through n – 1 within a section. A table view can have its own header and footer, distinct from any section; the table header appears before the first row of the first section, and the table footer appears after the last row of the last section. 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 8 About Table Views in iOS AppsAt a Glance A table view is an instance of the UITableView class in one of two basic styles, plain or grouped. A plain table view is an unbroken list; a grouped table view has visually distinct sections. A table view has a data source and might have a delegate. The data source object provides the data for populating the sections and rows of the table view. The delegate object customizes its appearance and behavior. Related chapters: “Table View Styles and Accessory Views” (page 12) Table Views Draw Their Rows Using Cells A table view draws its visible rows using cells—that is, UITableViewCell objects. Cells are views that can display text, images, or other kinds of content. They can have background views for both normal and selected states. Cells can also have accessory views, which function as controls for selecting or setting an option. The UIKit framework defines four standard cell styles, each with its own layout of the three default content elements: main label, detail label, and image. You may also create your own custom cellsto acquire a distinctive style for your app’s table views. When you configure the attributes of a table view in the storyboard editor, you choose between two types of cell content: static cells or dynamic prototypes. ● Static cells. Use static cells to design a table with a fixed number of rows, each with its own layout. Use static cells when you know what the table looks like at design time, regardless of the specific information it displays. ● Dynamic prototypes. Use dynamic prototypes to design one cell and then use it as the template for other cells in the table. Use a dynamic prototype when multiple cells in a table should use the same layout to display information. Dynamic prototype content is managed by the data source at runtime, with an arbitrary number of cells. Related Chapters: “Table View Styles and Accessory Views” (page 12), “A Closer Look at Table View Cells” (page 55) Responding to Selections of Rows When users select a row (by tapping it), the delegate of the table view is informed via a message. The delegate is passed the indexes of the row and the section that the row is in. It uses this information to locate the corresponding item in the app’s data model. This item might be at an intermediate level in the hierarchy of About Table Views in iOS Apps At a Glance 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 9data or it might be a “leaf node" in the hierarchy. If the item is at an intermediate level, the app displays a new table view. If the item is a leaf node, the app displays details about the selected item in a grouped-style table view or some other kind of view. In table views that list a series of options, tapping a row simply selects its associated option. No subsequent view of data is displayed. Related Chapters: “Navigating a Data Hierarchy with Table Views” (page 25), “Managing Selections” (page 74) In Editing Mode You Can Add, Delete, and Reorder Rows Table views can enter an editing mode in which users can insert or delete rows, or relocate them within the table. In editing mode, rows that are marked for insertion or deletion display a green plus sign (insertion) or a red minus sign (deletion) near the left edge of the row. If users touch a deletion control or, in some table views, swipe across a row, a red Delete button appears, prompting usersto delete that row. Rowsthat can be relocated display (near their right edge) an image consisting of several horizontal lines. When the table view leaves editing mode, the insertion, deletion, and reordering controls disappear. When users attempt to insert, delete, or reorder rows, the table view sends a sequence of messages to its data source and delegate so that they can manage these operations. Related Chapters: “Inserting and Deleting Rows and Sections” (page 80), “Managing the Reordering of Rows” (page 91) To Create a Table View, Use a Storyboard The easiest and recommended way to create and manage a table view is to use a custom UITableViewController object in a storyboard. If your app is based largely on table views, create your Xcode project using the Master-Detail Application template. This template includes an initial custom UITableViewController class and a storyboard for the scenes in the user interface, including the custom view controller and its table view. In the storyboard editor, choose one of the two styles for this table view and design its content. At runtime, UITableViewController creates the table view and assigns itself as delegate and data source. Immediately after it’s created, the table view asks its data source for the number of sections, the number of rows in each section, and the table view cell to use to draw each row. The data source manages the application data used for populating the sections and rows of the table view. About Table Views in iOS Apps At a Glance 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 10Related Chapters: “Navigating a Data Hierarchy with Table Views” (page 25), “Creating and Configuring a Table View” (page 36) Prerequisites Before reading this document, you should read Start Developing iOS Apps Today to understand the basic process for developing iOS apps. Then read View Controller Programming Guide for iOS for a comprehensive look at view controllers and storyboards. Finally, to gain valuable hands-on experience using table views in a storyboard, read the tutorial Your Second iOS App: Storyboards. The information presented in this introduction and in “Table View Styles and Accessory Views” (page 12) summarizes prescriptive information on table views presented in iOS Human Interface Guidelines. You can find a complete description of the styles and characteristics of table views, as well as their recommended uses, in the chapter “iOS UI Element Usage Guidelines”. See Also You will find the following sample code projects to be instructive models for your own table view implementations: ● SimpleDrillDown project ● Table View Animations and Gestures project For guidance on how to use the standard container view controllers provided by UIKit, see View Controller Catalog for iOS . This document describes split view controllers and navigation controllers, which can both contain table view controllers as children. About Table Views in iOS Apps Prerequisites 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 11Table views come in distinctive styles that are suitable for specific purposes. In addition, the UIKit framework provides standard styles for the cells used to draw the rows of table views. It also gives you standard accessory views (that is, controls) that you can include in cells. Table View Styles There are two major styles of table views: plain and grouped. The two styles are distinguished mainly by appearance. 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 12 Table View Styles and Accessory ViewsPlain Table Views A table view in the plain (or regular) style displays rows that stretch across the screen and have a creamy white background (see Figure 1-1). A plain table view can have one or more sections, sections can have one or more rows, and each section can have its own header or footer title. (A header or footer may also have a custom view, for instance one containing an image). When the user scrolls through a section with many rows, the header of the section floats to the top of the table view and the footer of the section floats to the bottom. Figure 1-1 A table view in the plain style A variation of plain table views associates an index with sections for quick navigation; Figure 1-2 shows an example of this kind of table view, which is called an indexed list. The index runs down the right edge of the table view. Entries in the index correspond to section header titles. Touching an item in the index scrolls the table view to the associated section. For example, the section headings could be two-letterstate abbreviations, Table View Styles and Accessory Views Table View Styles 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 13and the rows for a section could be the cities in that state; touching at a certain spot in the index displays the cities for the selected state. The rows in indexed lists should not have disclosure indicators or detail disclosure buttons, because these interfere with the index. Figure 1-2 A table view configured as an indexed list Table View Styles and Accessory Views Table View Styles 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 14The simplest kind of table view is a selection list (see Figure 1-3). A selection list is a plain table view that presents a menu of optionsthat users can select. It can limit the selection to one row or allow multiple selections. A selection list marks a selected row with a checkmark (see Figure 1-3). Figure 1-3 A table view configured as a selection list Grouped Table Views A grouped table view also displays a list of information, but it groups related rows in visually distinct sections. As shown in Figure 1-4, each section has rounded corners and by default appears against a bluish-gray background. Each section may have text or an image for its header or footer to provide some context or Table View Styles and Accessory Views Table View Styles 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 15summary for the section. A grouped table works especially well for displaying the most detailed information in a data hierarchy. It allows you to separate detailsinto conceptual groups and provide contextual information to help users understand it quickly. Figure 1-4 A table view in the grouped style Table View Styles and Accessory Views Table View Styles 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 16The headers and footers of sections in a grouped table view have relative locations and sizes as indicated in Figure 1-5. Figure 1-5 Header and footer of a section Padding Padding Header Table cell Footer On iPad devices, a grouped table view automatically gets wider margins when the table view itself is wide. Standard Styles for Table View Cells In addition to defining two styles of table views, the UIKit framework defines four styles for the cells that a table view uses to draw its rows. You may create custom table view cells with different appearances if you want, but these four predefined cell styles are suitable for most purposes. The techniques for creating table view cells in a predefined style and for creating custom cells are described in “A Closer Look at Table View Cells” (page 55). Table View Styles and Accessory Views Standard Styles for Table View Cells 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 17The defaultstyle for table view rows uses a simple cellstyle that has a single title and an optional image (Figure 1-6). This style is associated with the UITableViewCellStyleDefault constant. Figure 1-6 Default table row style Table View Styles and Accessory Views Standard Styles for Table View Cells 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 18The cell style for the rows in Figure 1-7 left-aligns the main title and puts a gray subtitle under it. It also permits an image in the default image location. This style is associated with the UITableViewCellStyleSubtitle constant. Figure 1-7 Table row style with a subtitle under the title Table View Styles and Accessory Views Standard Styles for Table View Cells 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 19The cell style for the rows in Figure 1-8 left-aligns the main title. It puts the subtitle in blue text and right-aligns it on the right side of the row. Images are not permitted. This style is used in the Settings app, where the subtitle indicatesthe currentsetting for a preference. It is associated with the UITableViewCellStyleValue1 constant. Figure 1-8 Table row style with a right-aligned subtitle Table View Styles and Accessory Views Standard Styles for Table View Cells 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 20The cell style for the rows in Figure 1-9 puts the main title in blue and right-aligns it at a point that’s indented from the left side of the row. The subtitle is left aligned at a short distance to the right of this point. This style does not allow images. It is used in the Contacts part of the Phone app and is associated with the UITableViewCellStyleValue2 constant. Figure 1-9 Table row style in Contacts format Accessory Views There are three standard kinds of accessory views (shown with their accessory-type constants): Standard accessory views Description Disclosure indicator—UITableViewCellAccessoryDisclosureIndicator. You use the disclosure indicator when selecting a cell results in the display of another table view reflecting the next level in the data model hierarchy. Detail disclosure button—UITableViewCellAccessoryDetailDisclosureButton. You use the detail disclosure button when selecting a cell resultsin a detail view of that item (which may or may not be a table view). Table View Styles and Accessory Views Accessory Views 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 21Standard accessory views Description Checkmark—UITableViewCellAccessoryCheckmark. You use a checkmark when a touch on a row results in the selection of that item. This kind of table view is known as a selection list, and it is analogous to a pop-up list. Selection lists can limit selections to one row, or they can allow multiple rows with checkmarks. Instead of the standard accessory views, you may specify a control (for example, a switch) or a custom view as the accessory view. Table View Styles and Accessory Views Accessory Views 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 22The table view programming interface includesseveral UIKit classes, two formal protocols, and a category added to a Foundation framework class. Table View A table view itself is an instance of the UITableView class. You use its methods to configure the appearance of the table view—for example,specifying the default height of rows or providing a subview used asthe header for the table. Other methods give you access to the currently selected row as well as specific rows or cells. You can call other methods of UITableView to manage selections, scroll the table view, and insert or delete rows and sections. UITableView inherits from the UIScrollView class, which defines scrolling behavior for views with content larger than the size of the window. UITableView redefines the scrolling behavior to allow vertical scrolling only. Table View Controller The UITableViewController class manages a table view and addssupport for many standard table-related behaviors such as selection management, row editing, table configuration, and others. This additional support is there to minimize the amount of code you have to write to create and initialize your table-based interface. You don’t use this class directly—instead you subclass UITableViewController to add custom behaviors. Data Source and Delegate A UITableView object must have a delegate and a data source. Following the Model-View-Controller design pattern, the data source mediates between the app’s data model (that is, its model objects) and the table view. The delegate, on the other hand, manages the appearance and behavior of the table view. The data source and the delegate are often (but not necessarily) the same object, and that object is usually a custom subclass of UITableViewController. (See “Navigating a Data Hierarchy with Table Views” (page 25) for further information.) 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 23 Overview of the Table View APIThe data source adoptsthe UITableViewDataSource protocol. UITableViewDataSource hastwo required methods. The tableView:numberOfRowsInSection: method tellsthe table view how many rowsto display in each section, and the tableView:cellForRowAtIndexPath: method provides the cell to display for each row in the table. Optional methods allow the data source to configure multiple sections, provide headers and/or footers, and support adding, removing, and reordering rows in the table. The delegate adoptsthe UITableViewDelegate protocol. This protocol has no required methods. It declares methods that allow the delegate to modify visible aspects of the table view, manage selections, support an accessory view, and support editing of individual rows in a table. An app can make use of the convenience class UILocalizedIndexedCollation to help the data source organize the data for indexed lists and display the proper section when users tap an item in the index. The UILocalizedIndexedCollation class also localizes section titles. Extension to the NSIndexPath Class Many table view methods use index paths as parameters or return values. An index path identifies a path to a specific node in a tree of nested arrays, and in the Foundation framework it isrepresented by an NSIndexPath object. UIKit declares a category on NSIndexPath with methods that return key paths, locate rows in sections, and construct NSIndexPath objects from row and section indexes. For more information, see NSIndexPath UIKit Additions. Table View Cells As noted in “Data Source and Delegate” (page 23), the data source must return a cell object for each visible row that a table view displays. These cell objects must inherit from the UITableViewCell class. This class includes methodsfor managing cellselection and editing, managing accessory views, and configuring the cell. You can instantiate cells directly in the standard styles defined by the UITableViewCell class and give these cells content consisting of one or two strings of text and, in some styles, both image and text. Instead of using a cell in a standard style, you can put your own custom subviews in the content view of an “off-the-shelf” cell object. You may also subclass UITableViewCell to customize the appearance and behavior of table view cells. These approaches are all discussed in “A Closer Look at Table View Cells” (page 55). Overview of the Table View API Extension to the NSIndexPath Class 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 24A common use of table views—and one to which they’re ideally suited—is to navigate hierarchies of data. A table view at a top level of the hierarchy lists categories of data at the most general level. Users select a row to “drill down” to the next level in the hierarchy. At the bottom of the hierarchy is a view (often a table view) that presents details about a specific item (for example, an address book record) and may allow users to edit the item. This section explains how you can map the levels of the data model hierarchy to a succession of table views and describes how you can use the facilities of the UIKit framework to help you implement such navigation-based apps. Hierarchical Data Models and Table Views For a navigation-based app, you typically design your app data as a graph of model objects that is sometimes referred to as the app’s data model. You can then implement the model layer of your app using various mechanisms or technologies, including Core Data, property lists, or archives of custom objects. Regardless of the approach, the traversal of your app’s data model follows patterns that are common to all navigation-based apps. The data model has hierarchical depth, and objects at variouslevels of this hierarchy should be the source for populating the rows of a table view. Note: To learn about the Core Data technology and framework, see Core Data Starting Point. The Data Model as a Hierarchy of Model Objects A well-designed app factors its classes and objects in a way that conforms to the Model-View-Controller (MVC) design pattern. The app’s data model consists of the model objects in this pattern. You can describe model objects (using the terminology provided by the object modeling pattern) in terms of their properties. These properties are of two general kinds: attributes and relationships. 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 25 Navigating a Data Hierarchy with Table ViewsNote: The notion of “property” here is abstractly related to, but not identical with, the declared property feature of Objective-C. A class definition typically represents properties programmatically through instance variables and declared properties. For more on declared properties, see The Objective-C Programming Language . To find out more about MVC and object modeling, read “Cocoa Design Patterns” in Cocoa Fundamentals Guide . Attributes represent elements of model-object data. Attributes can range from an instance of a primitive class (for example, an NSString, NSDate, or UIColor object) to a C structure or a simple scalar value. Attributes are generally what you use to populate a table view that represents a “leaf node” of the data hierarchy and that presents a detail view of that item. A model object may also have relationships with other model objects. It is through these relationships that a data model acquires hierarchical depth by composing an object graph. Relationships are of two general kinds in terms of cardinality: to-one and to-many. To-one relationships define an object’s relationship with another object (for example, a parent relationship). A to-many relationship, on the other hand, defines an object’s relationship with multiple objects of the same kind. The to-many relationship is characterized by containment and can be programmatically represented by collections such as NSArray objects (or, simply, arrays). An array might contain other arrays, or it could contain multiple dictionaries, which are collections that identify their contained valuesthrough keys. Dictionaries, in turn, can contain one or more other collections, including arrays, sets, and even other dictionaries. As collections nest in other collections, your data model can acquire hierarchical depth. Table Views and the Data Model The rows of a plain table view are typically backed by collection objects of the app’s data model; these objects are usually arrays. Arrays contain strings or other elements that a table view can use when displaying row content. When you create a table view (described in “Creating and Configuring a Table View” (page 36)), it immediately queries its data source for its dimensions—that is, it requests the number of sections and the number of rows per section—and then asks for the content of each row. The data source fetches this content from an array in the appropriate level of the data-model hierarchy. In many of the methods defined for a table view’s data source and delegate, the table view passes in an index path to identify the section and row that is the focus of the current operation—for example, fetching content for a row or indicating the row the user tapped. An index path is an instance of the Foundation framework’s NSIndexPath classthat you can use to identify an item in a tree of nested arrays. The UIKit framework extends NSIndexPath to add a section and a row property to the class. The data source should use these properties to map a section and row of the table view to a value at the corresponding index of the array being used as the table view’s source of data. Navigating a Data Hierarchy with Table Views Hierarchical Data Models and Table Views 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 26Note: The UIKit framework extension of the NSIndexPath class is described in NSIndexPath UIKit Additions. In the sequence of table views in Figure 3-1, the top level of the data hierarchy is an array of four arrays, with each inner array containing objects representing the trails for a particular region. When the user selects one of these regions, the next table view lists names identifying the trails within the selected array. When the user selects a particular trail, the next table view describes that trail using a grouped table view. Figure 3-1 Mapping levels of the data model to table views "Name" = "Sylvan Trail Loop" "Location" = "Edgewood City Park (Redwood City)" "Distance" = 2 "Difficulty" = "Moderate" "Restrictions" = "No bicycles, pets, or horses" "Map" = pen_map6.png // other key/value pairs Alambique-Skyline Sweeny Ridge Sawyer Camp Trail Purisima Creek Dean-Crystal Springs Sylvan Trail Loop regions array trails array trail dictionary East Bay North Bay Peninsula South Bay Navigating a Data Hierarchy with Table Views Hierarchical Data Models and Table Views 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 27Note: You could easily redesign the app in Figure 3-1 (page 27) to have only two table views. The first table view would be an indexed list of trails by region. The second table view would display the detail for a selected trail. View Controllers and Navigation-Based Apps The UIKit framework provides a number of view controller classesfor managing common user interface patterns in iOS. View controllers are controller objects that inherit from the UIViewController class. They are an essential tool for view management, especially when an app uses those views to present successive levels of its data hierarchy. This section describes how two subclasses of UIViewController, navigation controllers and table view controllers, present and manage a succession of table views. Note: Thissection gives an overview of view controllersto provide some background for the coding tasks discussed later in this document. To learn about view controllers in depth, see View Controller Programming Guide for iOS . Navigation Controllers The UINavigationController classinheritsfromUIViewController, a base classthat definesthe common programmatic interface and behavior for controller objects that manage views in iOS. Through inheritance from this base class, a view controller acquires an interface for general view management. After it implements parts of thisinterface, a view controller can autorotate its view, respond to low-memory notifications, overlay “modal” views, respond to taps on the Edit button, and otherwise manage the view. A navigation controller maintains a stack of view controllers, one for each of the table views displayed (see Figure 3-2). It begins with what’s known as the root view controller. When the user taps a row of the table view (often on a detail disclosure button), the root view controller pushes the next view controller onto the stack. The new view controller’s table view visually slides into place from the right, and the navigation bar Navigating a Data Hierarchy with Table Views View Controllers and Navigation-Based Apps 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 28items are updated appropriately. When users tap the back button in the navigation bar, the current view controller is popped off the stack. As a consequence, the navigation controller displaysthe table view managed by the view controller that is now at the top of the stack. Figure 3-2 Navigation controller and view controllers in a navigation-based app UITableView UIViewController UINavigationController UINavigationBar Navigation Bars Navigation bars are a user-interface device that enables users to navigate a hierarchy of data. Users start with general, top-level items and “drill down” the hierarchy to detailed viewsshowing specific properties of leaf-node items. The view below the navigation bar presents the current level of data. A navigation bar includes a title for the current view and, if that view is lower in the hierarchy than the top level, a back button on the left side of the bar; the back button is a navigation control that the user taps to return to the previous level. (The back Navigating a Data Hierarchy with Table Views View Controllers and Navigation-Based Apps 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 29button by default displaysthe title for the previous view.) A navigation bar may also have an Edit button—used to enter editing mode for the current view—or custom buttons for functions that manage content (see Figure 3-3). Figure 3-3 Navigation bars and common control items Navigational control Controls to manage content A UINavigationController manages the navigation bar, including the items that are displayed in the bar for the view below it. A UIViewController object manages a view displayed below the navigation bar. For this view controller, you create a subclass of UIViewController or a subclass of a view controller class that the UIKit framework provides for managing a particular type of view. For table views, this view controller class is UITableViewController. For a navigation controller that displays a sequence of table views reflecting levels within a data hierarchy, you need to create a separate custom table view controller for each table view. The UIViewController class includes methods that let view controllers access and set the navigation items displayed in the navigation bar for the currently displayed table view. This class also declares a title property through which you can set the title of the navigation bar for the current table view. Navigating a Data Hierarchy with Table Views View Controllers and Navigation-Based Apps 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 30Table View Controllers Although you could manage a table view using a direct subclass of UIViewController, you save yourself a lot of work if instead you subclass UITableViewController. The UITableViewController class takes care of many of the details you would have to implement if you created a directsubclass of UIViewController to manage a table view. The recommended way to create a table view controller is to specify it in a storyboard. The associated table view isloaded from the storyboard, along with the table view’s attributes,size, and autoresizing characteristics. The table view controller sets itself as the data source and the delegate of the table view. Note: You can create a table view controller programmatically by allocating memory for it and initializing it with the initWithStyle: method, passing in either UITableViewStylePlain or UITableViewStyleGrouped for the required table view style. When the table view is about to appear for the first time, the table view controller sends reloadData to the table view, which prompts it to request data from its data source. The data source tells the table view how many sections and rows per section it wants, and then gives the table view the data to display in each row. This process is described in “Creating and Configuring a Table View” (page 36). The UITableViewController class also performs other common tasks. It clears selections when the table view is about to be displayed and flashes the scroll indicators when the table finishes displaying. In addition, it responds properly when users tap the Edit button by putting the table view into editing mode (or taking it out of editing mode if users tap Done). The class exposes one property, tableView, which gives you access to the managed table view. Note: A table view controller supports inline editing of table view rows; if, for example, rows have embedded text fields in editing mode, it scrolls the row being edited above the virtual keyboard that is displayed. It also supports the NSFetchedResultsController class for managing the results returned from a Core Data fetch request. The UITableViewController class implements the foregoing behavior by overriding loadView, viewWillAppear:, and other methods inherited from UIViewController. In your subclass of UITableViewController, you may also override these methods to acquire specialized behavior. If you do override these methods, be sure to invoke the superclass implementation of the method, usually as the first method call, to get the default behavior. Navigating a Data Hierarchy with Table Views View Controllers and Navigation-Based Apps 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 31Note: You should use a UIViewController subclass rather than a subclass of UITableViewController to manage a table view if the view to be managed is composed of multiple subviews, only one of which is a table view. The default behavior of the UITableViewController class is to make the table view fill the screen between the navigation bar and the tab bar (if either are present). If you decide to use a UIViewController subclass rather than a subclass of UITableViewController to manage a table view, you should perform a couple of the tasks mentioned above to conform to the human interface guidelines. To clear any selection in the table view before it’s displayed, implement the viewWillAppear: method to clear the selected row (if any) by calling deselectRowAtIndexPath:animated:. After the table view has been displayed, you should flash the scroll view’sscroll indicators by sending a flashScrollIndicators message to the table view; you can do this in an override of the viewDidAppear: method of UIViewController. Managing Table Views in a Navigation-Based App A UITableViewController object—or any other object that assumes the roles of data source and delegate for a table view—must respond to messages sent by the table view in order to populate its rows, configure it, respond to selections, and manage editing sessions. In the rest of this document, you learn how to do these things. However, there are certain other things you need to do to ensure the proper display of a sequence of table views in a navigation-based app. Note: Thissection summarizes view-controller and navigation-controller tasks, with a focus on table views. For a thorough discussion of view controllers and navigation controllers, including the complete details of their implementation, see View Controller Programming Guide for iOS and View Controller Catalog for iOS . At this point, let’s assume that a table view managed by a table view controller presents a list to the user. How does the app display the next table view in the sequence? When a user taps a row of the table view, the table view callsthe tableView:didSelectRowAtIndexPath: or tableView:accessoryButtonTappedForRowWithIndexPath:method implemented by the delegate. (That latter method is invoked if the user taps a row’s detail disclosure button.) The delegate creates the table view controller managing the next table view in the sequence, sets the data it needs to populate its table view, and pushes this new view controller onto the navigation controller’s stack of view controllers. A storyboard provides the specification that allows UIKit to perform most of this work for you. Navigating a Data Hierarchy with Table Views View Controllers and Navigation-Based Apps 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 32Storyboards represent the screens in an app and the transitions between them. The storyboard in a basic app may contain just a few screens, but a more complex app might have multiple storyboards, each of which represents a different subset of its screens. The storyboard example in Figure 3-4 presents a graphical representation of each scene, its contents, and its connections. Figure 3-4 A storyboard with two table view controllers A scene represents an onscreen content area that is managed by a view controller. (In the context of a storyboard, scene and view controller are synonymous terms.) The leftmost scene in the default storyboard represents a navigation controller. A navigation controller is a container view controller because, in addition to its views, it also manages a set of other view controllers. For example, the navigation controller in Figure 3-4 (page 33) manages the master and detail view controllers, in addition to the navigation bar and the back button that you see when you run the app. A relationship is a type of connection between scenes. In Figure 3-4, there is a relationship between the navigation controller and the master scene. In this case, the relationship represents the containment of the master and detailscenes by the navigation controller. When the app runs, the navigation controller automatically loads the master scene and displays the navigation bar at the top of the screen. A segue represents a transition from one scene (called the source) to the next scene (called the destination). For example, in Figure 3-4, the master scene is the source and the detail scene is the destination. When you select the Detail item in the master list, you trigger a segue from the source to the destination. In this case, the segue is a push segue, which means that the destination scene slides over the source scene from right to left. As the detail screen is revealed, a back button appears at the left end of the navigation bar, titled with the previous screen’s title (in this case, “Master”). The back button is provided automatically by the navigation controller that manages the master-detail hierarchy. Navigating a Data Hierarchy with Table Views View Controllers and Navigation-Based Apps 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 33Storyboards make it easy to pass data from one scene to another via the prepareForSegue:sender: method of the UIViewController class. This method is called when the first scene (the source) is about to transition to the next scene (the destination). The source view controller can implement prepareForSegue:sender: to perform setup tasks, such as passing information to the destination view controller about what it should display in its table view. Listing 3-1 shows one implementation of this method. Listing 3-1 Passing data to a destination view controller - (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender { if ([[segue identifier] isEqualToString:@"ShowDetails"]) { MyDetailViewController *detailViewController = [segue destinationViewController]; NSIndexPath *indexPath = [self.tableView indexPathForSelectedRow]; detailViewController.data = [self.dataController objectInListAtIndex:indexPath.row]; } } A segue represents a one-way transition from a source scene to a destination scene. One of the consequences of this design is that you can use a segue to pass data to a destination, but you can’t use a segue to send data from a destination to its source. To solve this problem, you create a delegate protocol that declares methods that the destination view controller calls when it needs to pass back some data. Listing 3-2 shows one implementation of a protocol for passing data back to a source view controller. Listing 3-2 Passing data to a source view controller @protocol MyAddViewControllerDelegate - (void)addViewControllerDidCancel:(MyAddViewController *)controller; - (void)addViewControllerDidFinish:(MyAddViewController *)controller data:(NSString *)item; @end - (void)addViewControllerDidCancel:(MyAddViewController *)controller { [self dismissViewControllerAnimated:YES completion:NULL]; } Navigating a Data Hierarchy with Table Views View Controllers and Navigation-Based Apps 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 34- (void)addViewControllerDidFinish:(MyAddViewController *)controller data:(NSString *)item { if ([item length]) { [ self.dataController addData:item]; [[self tableView] reloadData]; } [self dismissViewControllerAnimated:YES completion:NULL]; } Note: The full details of creating storyboards are described in Xcode 4 User Guide . To learn more about using view controllers in storyboards, see View Controller Programming Guide for iOS . Design Pattern for Navigation-Based Apps A navigation-based app with table views should follow these design best practices: ● A view controller (typically a subclass of UITableViewController), acting in the role of data source, populates its table view with data from an object representing a level of the data hierarchy. When the table view displays a list of items, the object is typically an array. When the table view displays item detail (that is, a leaf node of the data hierarchy), the object can be a custom model object, a Core Data managed object, a dictionary, or something similar. ● The view controller stores the data it needs for populating its table view. The view controller can use this data directly for populating the table view, or it can use it to fetch or otherwise obtain the necessary data. When you design your view controller subclass, you should define a property to hold this data. View controllers should not obtain the data for their table view through a global variable or a singleton objectsuch asthe app delegate. Such direct dependencies make your code lessreusable and more difficult to test and debug. ● The current view controller on top of the navigation-controller stack creates the next view controller in the sequence and, before it pushes it onto the stack, sets the data that this view controller, acting as data source, needs to populate its table view. Navigating a Data Hierarchy with Table Views Design Pattern for Navigation-Based Apps 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 35Your app must present a table view to users before it can manage it in response to taps on rows and other actions. This chapter shows what you must do to create a table view, configure it, and populate it with data. Most of the code examples shown in this chapter come from the sample projects TableViewSuite and TheElements. Basics of Table View Creation To create a table view, several entities in an app must interact: the view controller, the table view itself, and the table view’s data source and delegate. The view controller, data source, and delegate are usually the same object. The view controller starts the calling sequence, diagrammed in Figure 4-1 (page 37). 1. The view controller creates a UITableView instance in a certain frame and style. It can do this either programmatically or in a storyboard. The frame is usually set to the screen frame, minus the height of the status bar or, in a navigation-based app, to the screen frame minus the heights of the status bar and the navigation bar. The view controller may also set global properties of the table view at this point, such as its autoresizing behavior or a global row height. To learn how to create table views in a storyboard and programmatically, see “Creating a Table View Using a Storyboard” (page 38) and “Creating a Table View Programmatically” (page 43). 2. The view controllersetsthe data source and delegate of the table view and sends a reloadData message to it. The data source must adopt the UITableViewDataSource protocol, and the delegate must adopt the UITableViewDelegate protocol. 3. The data source receives a numberOfSectionsInTableView: message from the UITableView object and returns the number of sections in the table view. Although this is an optional protocol method, the data source must implement it if the table view has more than one section. 4. For each section, the data source receives a tableView:numberOfRowsInSection: message and responds by returning the number of rows for the section. 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 36 Creating and Configuring a Table View5. The data source receives a tableView:cellForRowAtIndexPath: message for each visible row in the table view. It responds by configuring and returning a UITableViewCell object for each row. The UITableView object uses this cell to draw the row. Figure 4-1 Calling sequence for creating and configuring a table view tableView: cellForRowAtIndexPath: Set data source and delegate Client Data Source Table View initWithFrame:style: numberOfSectionsInTableView: tableView:numberOfRowsInSection: The diagram in Figure 4-1 shows the required protocol methods as well as the numberOfSectionsInTableView: method. Populating the table view with data occurs in steps 3 through 5. To learn how to implement the methods in these steps, see “Populating a Dynamic Table View with Data” (page 44). The data source and the delegate may implement other optional methods of their protocolsto further configure the table view. For example, the data source might want to provide titles for each of the sections in the table view by implementing the tableView:titleForHeaderInSection: method. For more on some of these optional table view customizations, see “Optional Table View Configurations” (page 52). You create a table view in either the plain style (UITableViewStylePlain) or the grouped style (UITableViewStyleGrouped). (You specify the style in a storyboard.) Although the procedure for creating a table view in eitherstylesisidentical, you may want to perform different kinds of configurations. For example, because a grouped table view generally presents item detail, you may also want to add custom accessory views (for example, switches and sliders) or custom content (for example, text fields). For an example, see “A Closer Look at Table View Cells” (page 55). Creating and Configuring a Table View Basics of Table View Creation 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 37Recommendations for Creating and Configuring Table Views There are many ways to put together a table view app. For example, you can use an instance of a custom NSObject subclass to create, configure, and manage a table view. However, you will find the task much easier if you adopt the classes, techniques, and design patterns that the UIKit framework offers for this purpose. The following approaches are recommended: ● Use an instance of a subclass of UITableViewController to create and manage a table view. Most apps use a custom UITableViewController object to manage a table view. As described in “Navigating a Data Hierarchy with Table Views” (page 25), UITableViewController automatically creates a table view, assignsitself as both delegate and data source (and adoptsthe corresponding protocols), and initiates the procedure for populating the table view with data. It also takes care of several other “housekeeping” details of behavior. The behavior of UITableViewController (a subclass of UIViewController) within the navigation controller architecture is described in “Table View Controllers” (page 31). ● If your app is largely based on table views, select the Master-Detail Application template provided by Xcode when you create your project. As described in “Creating a Table View Using a Storyboard” (page 38), the template includes stub code and a storyboard defining an app delegate, the navigation controller, and the master view controller (which is an instance of a custom subclass of UITableViewController). ● For successive table views, you should implement custom UITableViewController objects. You can either load them from a storyboard or create the associated table views programmatically. Although either option is possible, the storyboard route is generally easier. If the view to be managed is a composite view in which a table view is one of multiple subviews, you must use a custom subclass of UIViewController to manage the table view (and other views). Do not use UITableViewController, because this controller class sizes the table view to fill the screen between the navigation bar and the tab bar (if either is present). Creating a Table View Using a Storyboard Create an app with a table view using Xcode. When you create your project, select a template that contains stub code and a storyboard that, by default, supply the structure for setting up and managing table views. To create an app structured around table views 1. In Xcode, choose File > New > Project. Creating and Configuring a Table View Recommendations for Creating and Configuring Table Views 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 382. In the iOS section at the left side of the dialog, select Application. 3. In the main area of the dialog, select Master-Detail Application and then click Next. 4. Choose your project options (make sure Use Storyboard is selected), and then click Next. 5. Choose a save location for your project and then click Create. Depending on which device family you chose in step 4, the project has one or two storyboards. To display the storyboard canvas, double-click a storyboard file in the project navigator. If the device family is iPhone, for example, your storyboard should contain a table view controller that looks similar to the one in Figure 4-2. Figure 4-2 The master view controller in the Master-Detail Application storyboard To make sure that the scene on the canvas represents the master view controller class in your code 1. On the canvas, click the scene’s title bar to select the table view controller. 2. Click the Identity button at the top of the utility area to open the Identity inspector. 3. Verify that the Class field contains the project’s custom subclass of UITableViewController. Choose the Table View’s Display Style As described in “Table View Styles” (page 12), every table view has a display style: plain or grouped. To choose the display style of a table view in a storyboard 1. Click the center of the scene to select the table view. Creating and Configuring a Table View Creating a Table View Using a Storyboard 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 392. In the utility area, display the Attributes inspector. 3. In the Table View section of the Attributes inspector, use the Style pop-up menu to choose Plain or Grouped. Choose the Table View’s Content Type Storyboards introduce two convenient ways to design a table view’s content: ● Dynamic prototypes. Design a prototype cell and then use it as the template for other cells in the table. Use a dynamic prototype when multiple cells in a table should use the same layout to display information. Dynamic content is managed by the table view data source (the table view controller) at runtime, with an arbitrary number of cells. Figure 4-3 shows a plain table view with a one prototype cell. Figure 4-3 A dynamic table view Note: If a table view in a storyboard is dynamic, the custom subclass of UITableViewController that contains the table view needs to implement the data source protocol. For more information, see “Populating a Dynamic Table View with Data” (page 44). Creating and Configuring a Table View Creating a Table View Using a Storyboard 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 40● Static cells. Use static content to design the overall layout of the table, including the total number of cells. A table view with static content has a fixed set of cells that you can configure at design time. You can also configure otherstatic data elementssuch assection headers. Use static cells when a table does not change its layout, regardless of the specific information it displays. Figure 4-4 shows a grouped table view with three static cells. Figure 4-4 A static table view Note: If a table view in a storyboard isstatic, the custom subclass of UITableViewController that contains the table view should not implement the data source protocol. Instead, the table view controllershould use its viewDidLoad method to populate the table view’s data. For more information, see “Populating a Static Table View With Data” (page 46). By default, when you add a table view controller to a storyboard, the controller contains a table view that uses prototype-based cells. If you want to use static cells: 1. Select the table view. 2. Display the Attributes inspector. 3. In the the Content pop-up menu, choose Static Cells. Creating and Configuring a Table View Creating a Table View Using a Storyboard 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 41If you’re designing a prototype cell, the table view needs a way to identify the prototype when the data source dequeues reusable cells for the table at runtime. Therefore you must assign a reuse identifier to the cell. In the Table View Cell section of the Attributes inspector, enter an ID in the Identifier text field. By convention, a cell’s reuse identifier should describe what the cell contains, such as BirdSightingCell. Design the Table View’s Rows As described in “Standard Styles for Table View Cells” (page 17), UIKit defines four styles for the cells that a table view uses to draw its rows. You can use one of the four standard styles, design a custom style, or subclass UITableViewCell to define additional behavior or properties for the cell. This topic is covered in detail in “A Closer Look at Table View Cells” (page 55). A table view cell can also have an accessory, as described in “Accessory Views” (page 21). An accessory is a standard user interface element that UIKit draws at the right end of a table cell. For example, the disclosure indicator, which looks similar to a right angle bracket (>), tells users that tapping an item reveals related information in a new screen. In the Attributes inspector, use the Accessory pop-up menu to select a cell’s accessory. Create Additional Table Views If your app displays and manages more than one table view, add those table views to your storyboard. You add a table view by adding a custom UITableViewController object, which contains the table view it manages. To add custom class files to your project 1. In Xcode, choose File > New > File. 2. In the iOS section at the left side of the dialog, select Cocoa Touch. 3. In the main area of the dialog, select Objective-C class, and then click Next. 4. Enter a name for your new class, choose subclass of UITableViewController, and then click Next. 5. Choose a save location for your class files, and then click Create. To add a table view controller to a storyboard 1. Display the storyboard to which you want to add the table view controller. 2. Drag a table view controller out of the object library and drop it on the storyboard. 3. With the new scene still selected on the canvas, click the Identity button in the utility area to open the Identity inspector. Creating and Configuring a Table View Creating a Table View Using a Storyboard 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 424. In the Custom Class section, choose the new custom class in the Class pop-up menu. 5. Set the new table view’s style and cell content (dynamic or static). 6. Create a segue to the new scene. The details of step 7 vary depending on the project. To learn more about adding segues, see Xcode 4 User Guide . Note: Populating a table view with data and configuring a table view are discussed in “Populating a Dynamic Table View with Data” (page 44) and “Optional Table View Configurations” (page 52). Learn More by Creating a Sample App The tutorial Your Second iOS App: Storyboards shows how to create a sample app that is structured around table views. After you complete the steps in this tutorial, you’ll have a working knowledge of how to create both dynamic and static table views using a storyboard. The tutorial creates a basic navigation-based app called BirdWatching that uses table view controllers connected by both push and modal segues. Creating a Table View Programmatically If you choose not to use UITableViewController for table view management, you must replicate what this class gives you “for free.” Adopt the Data Source and Delegate Protocols The class creating the table view typically makes itself the data source and delegate by adopting the UITableViewDataSource and UITableViewDelegate protocols. The adoption syntax appears just after the superclass in the @interface directive, as shown in Listing 4-1. Listing 4-1 Adopting the data source and delegate protocols @interface RootViewController : UIViewController @property (nonatomic, strong) NSArray *timeZoneNames; @end Creating and Configuring a Table View Creating a Table View Programmatically 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 43Create and Configure a Table View The next step is for the client to allocate and initialize an instance of the UITableView class. Listing 4-2 gives an example of a client that creates a UITableView object in the plain style, specifies its autoresizing characteristics, and then sets itself to be both data source and delegate. Again, keep in mind that the UITableViewController does all of this for you automatically. Listing 4-2 Creating a table view - (void)loadView { UITableView *tableView = [[UITableView alloc] initWithFrame:[[UIScreen mainScreen] applicationFrame] style:UITableViewStylePlain]; tableView.autoresizingMask = UIViewAutoresizingFlexibleHeight|UIViewAutoresizingFlexibleWidth; tableView.delegate = self; tableView.dataSource = self; [tableView reloadData]; self.view = tableView; } Because in this example the class creating the table view is a subclass of UIViewController, it assigns the created table view to its view property, which it inherits from that class. It also sends a reloadData message to the table view, causing the table view to initiate the procedure for populating its sections and rows with data. Populating a Dynamic Table View with Data Just after a table view object is created, it receives a reloadData message, which tells it to start querying the data source and delegate for the information it needs for the sections and rows it displays. The table view immediately asks the data source for its logical dimensions—that is, the number of sections and the number of rows in each section. It then repeatedly invokes the tableView:cellForRowAtIndexPath: method to get a cell object for each visible row; it uses this UITableViewCell object to draw the content of the row. (Scrolling a table view also causes an invocation of tableView:cellForRowAtIndexPath: for each newly visible row.) Creating and Configuring a Table View Populating a Dynamic Table View with Data 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 44As noted in “Choose the Table View’s Content Type” (page 40), if the table view is dynamic then you need to implement the required data source methods. Listing 4-3 shows an example of how the data source and the delegate could configure a dynamic table view. Listing 4-3 Populating a dynamic table view with data - (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView { return [regions count]; } - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { // Number of rows is the number of time zones in the region for the specified section. Region *region = [regions objectAtIndex:section]; return [region.timeZoneWrappers count]; } - (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section { // The header for the section is the region name -- get this from the region at the section index. Region *region = [regions objectAtIndex:section]; return [region name]; } - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *MyIdentifier = @"MyReuseIdentifier"; UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:MyIdentifier]; if (cell == nil) { cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:MyIdentifier]]; } Region *region = [regions objectAtIndex:indexPath.section]; Creating and Configuring a Table View Populating a Dynamic Table View with Data 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 45TimeZoneWrapper *timeZoneWrapper = [region.timeZoneWrappers objectAtIndex:indexPath.row]; cell.textLabel.text = timeZoneWrapper.localeName; return cell; } The data source, in its implementation of the tableView:cellForRowAtIndexPath: method, returns a configured cell object that the table view can use to draw a row. For performance reasons, the data source tries to reuse cells as much as possible. It first asks the table view for a specific reusable cell object by sending it a dequeueReusableCellWithIdentifier: message. If no such object exists, the data source creates it, assigning it a reuse identifier. The data source sets the cell’s content (in this example, its text) and returns it. “A Closer Look at Table View Cells” (page 55) discusses this data source method and UITableViewCell objects in more detail. If the dequeueReusableCellWithIdentifier: method asks for a cell that’s defined in a storyboard, the method always returns a valid cell. If there is not a recycled cell waiting to be reused, the method creates a new one using the information in the storyboard itself. This eliminates the need to check the return value for nil and create a cell manually. The implementation of the tableView:cellForRowAtIndexPath: method in Listing 4-3 includes an NSIndexPath argument that identifies the table view section and row. UIKit declares a category of the NSIndexPath class, which is defined in the Foundation framework. This category extends the class to enable the identification of table view rows by section and row number. For more information on this category, see NSIndexPath UIKit Additions. Populating a Static Table View With Data As noted in “Choose the Table View’s Content Type” (page 40), if a table view is static then you should not implement any data source methods. The configuration of the table view is known at compile time, so UIKit can get this information from the storyboard at runtime. However, you still need to populate a static table view with data from your data model. “Populating a Static Table View With Data” shows an example of how a table view controller could load user data in a static table view. This example is adapted from Your Second iOS App: Storyboards. Listing 4-4 Populating a static table view with data - (void)viewDidLoad { Creating and Configuring a Table View Populating a Static Table View With Data 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 46[super viewDidLoad]; BirdSighting *theSighting = self.sighting; static NSDateFormatter *formatter = nil; if (formatter == nil) { formatter = [[NSDateFormatter alloc] init]; [formatter setDateStyle:NSDateFormatterMediumStyle]; } if (theSighting) { self.birdNameLabel.text = theSighting.name; self.locationLabel.text = theSighting.location; self.dateLabel.text = [formatter stringFromDate:(NSDate*)theSighting.date]; } } The table view is populated with data in the UIViewController method viewDidLoad, which is called after the view is loaded into memory. The data is passed to the table view controller in the sighting object, which isset in the previous view controller’s prepareForSegue:sender: method. The properties birdNameLabel, locationLabel, and dateLabel are outlets connected to labelsin the static table view (see Figure 4-4 (page 41)). Populating an Indexed List An indexed list (see Figure 1-2 (page 14)) is ideally suited for navigating large amounts of data organized by a conventional ordering scheme such as an alphabet. An indexed list is a table view in the plain style that is specially configured through three UITableViewDataSource methods: ● sectionIndexTitlesForTableView: Returns an array of the strings to use as the index entries (in order). ● tableView:titleForHeaderInSection: Maps these index strings to the titles of the table view’s sections (they don’t have to be the same). ● tableView:sectionForSectionIndexTitle:atIndex: Returns the section index related to the entry the user tapped in the index. Creating and Configuring a Table View Populating an Indexed List 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 47The data you use to populate an indexed list should be organized to reflect this indexing model. Specifically, you need to build an array of arrays. Each inner array corresponds to a section in the table. Section arrays are sorted (or collated) within the outer array according to the prevailing ordering scheme, which is often an alphabetical scheme (for example, A through Z). Additionally, the items in each section array are sorted. You can build and sort this array of arrays yourself, but fortunately the UILocalizedIndexedCollation class greatly simplifies the tasks of building and sorting these data structures and providing data to the table view. The class also collates items in the arrays according to the current localization. However you internally manage this array-of-arrays structure is up to you. The objects to be collated should have a property or method that returns a string value that the UILocalizedIndexedCollation class uses in collation; if it is a method, it should have no parameters. You might find it convenient to define a custom model class whose instances represent the rows in the table view. These model objects not only return a string value but also define a property that holdsthe index of the section array to which the object is assigned. Listing 4-5 illustrates the definition of a class that declares a name property and a sectionNumber property. Listing 4-5 Defining the model-object interface @interface State : NSObject @property(nonatomic,copy) NSString *name; @property(nonatomic,copy) NSString *capitol; @property(nonatomic,copy) NSString *population; @property NSInteger sectionNumber; @end Before your table view controller is asked to populate the table view, you load the data to be used (from whatever source) and create instances of your model class from this data. The example in Listing 4-6 loads data defined in a property list and creates the model objects from that. It also obtains the shared instance of UILocalizedIndexedCollation and initializes the mutable array (states) that will contain the section arrays. Listing 4-6 Loading the table-view data and initializing the model objects - (void)viewDidLoad { [super viewDidLoad]; UILocalizedIndexedCollation *theCollation = [UILocalizedIndexedCollation currentCollation]; self.states = [NSMutableArray arrayWithCapacity:1]; Creating and Configuring a Table View Populating an Indexed List 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 48NSString *thePath = [[NSBundle mainBundle] pathForResource:@"States" ofType:@"plist"]; NSArray *tempArray; NSMutableArray *statesTemp; if (thePath && (tempArray = [NSArray arrayWithContentsOfFile:thePath]) ) { statesTemp = [NSMutableArray arrayWithCapacity:1]; for (NSDictionary *stateDict in tempArray) { State *aState = [[State alloc] init]; aState.name = [stateDict objectForKey:@"Name"]; aState.population = [stateDict objectForKey:@"Population"]; aState.capitol = [stateDict objectForKey:@"Capitol"]; [statesTemp addObject:aState]; } } else { return; } After the data source has this “raw” array of model objects, it can process it with the facilities of the UILocalizedIndexedCollation class. In Listing 4-7, the code is annotated with numbers. Listing 4-7 Preparing the data for the indexed list // viewDidLoad continued... // (1) for (State *theState in statesTemp) { NSInteger sect = [theCollation sectionForObject:theState collationStringSelector:@selector(name)]; theState.sectionNumber = sect; } // (2) NSInteger highSection = [[theCollation sectionTitles] count]; NSMutableArray *sectionArrays = [NSMutableArray arrayWithCapacity:highSection]; for (int i = 0; i < highSection; i++) { NSMutableArray *sectionArray = [NSMutableArray arrayWithCapacity:1]; [sectionArrays addObject:sectionArray]; } Creating and Configuring a Table View Populating an Indexed List 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 49// (3) for (State *theState in statesTemp) { [(NSMutableArray *)[sectionArrays objectAtIndex:theState.sectionNumber] addObject:theState]; } // (4) for (NSMutableArray *sectionArray in sectionArrays) { NSArray *sortedSection = [theCollation sortedArrayFromArray:sectionArray collationStringSelector:@selector(name)]; [self.states addObject:sortedSection]; } } // end of viewDidLoad Here's what the code in Listing 4-7 does: 1. The data source enumerates the array of model objects and sends sectionForObject:collationStringSelector: to the collation manager on each iteration. This method takes as arguments a model object and a property or method of the object that it usesin collation. Each call returns the index of the section array to which the model object belongs, and that value is assigned to the sectionNumber property. 2. The data source source then creates a (temporary) outer mutable array and mutable arraysfor each section; it adds each created section array to the outer array. 3. It then enumerates the array of model objects and adds each object to its assigned section array. 4. The data source enumerates the array of section arrays and calls sortedArrayFromArray:collationStringSelector: on the collation manager to sort the items in each array. It passes in a section array and a property or method that is to be used in sorting the items in the array. Each sorted section array is added to the final outer array. Now the data source is ready to populate its table view with data. It implements the methods specific to indexed lists as shown in Listing 4-8. In doing this it calls two UILocalizedIndexedCollation methods: sectionIndexTitles and sectionForSectionIndexTitleAtIndex:. Also note that in tableView:titleForHeaderInSection: itsuppresses any headersfrom appearing in the table view when the associated section does not have any items. Listing 4-8 Providing section-index data to the table view - (NSArray *)sectionIndexTitlesForTableView:(UITableView *)tableView { Creating and Configuring a Table View Populating an Indexed List 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 50return [[UILocalizedIndexedCollation currentCollation] sectionIndexTitles]; } - (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section { if ([[self.states objectAtIndex:section] count] > 0) { return [[[UILocalizedIndexedCollation currentCollation] sectionTitles] objectAtIndex:section]; } return nil; } - (NSInteger)tableView:(UITableView *)tableView sectionForSectionIndexTitle:(NSString *)title atIndex:(NSInteger)index { return [[UILocalizedIndexedCollation currentCollation] sectionForSectionIndexTitleAtIndex:index]; } Finally, the data source should implement the UITableViewDataSource methods that are common to all table views. Listing 4-9 gives examples of these implementations, and illustrates how to use the section and row properties of the table view–specific category of the NSIndexPath class described in NSIndexPath UIKit Additions. Listing 4-9 Populating the rows of an indexed list - (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView { return [self.states count]; } - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { return [[self.states objectAtIndex:section] count]; } - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *CellIdentifier = @"StateCell"; Creating and Configuring a Table View Populating an Indexed List 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 51UITableViewCell *cell; cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; if (cell == nil) { cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier]]; } State *stateObj = [[self.states objectAtIndex:indexPath.section] objectAtIndex:indexPath.row]; cell.textLabel.text = stateObj.name; return cell; } For table views that are indexed lists, when the data source assigns cells for rows in tableView:cellForRowAtIndexPath:, it should ensure that the accessoryType property of the cell is set to UITableViewCellAccessoryNone. After initially populating the table view following the procedure outlined above, you can reload the contents of the index by calling the reloadSectionIndexTitles method. Optional Table View Configurations The table view API allows you to configure various visual and behavioral aspects of a table view, including specific rows and sections. The following examples serve to give you some idea of the options available to you. Add a Custom Title In the same block of code that createsthe table view, you can apply global configurations using certain methods of the UITableView class. The code example in Listing 4-10 adds a custom title for the table view (using a UILabel object). Listing 4-10 Adding a title to the table view - (void)loadView { CGRect titleRect = CGRectMake(0, 0, 300, 40); UILabel *tableTitle = [[UILabel alloc] initWithFrame:titleRect]; Creating and Configuring a Table View Optional Table View Configurations 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 52tableTitle.textColor = [UIColor blueColor]; tableTitle.backgroundColor = [self.tableView backgroundColor]; tableTitle.opaque = YES; tableTitle.font = [UIFont boldSystemFontOfSize:18]; tableTitle.text = [curTrail objectForKey:@"Name"]; self.tableView.tableHeaderView = tableTitle; [self.tableView reloadData]; } Provide a Section Title The example in Listing 4-11 returns a title string for a section. Listing 4-11 Returning a title for a section - (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section { // Returns section title based on physical state: [solid, liquid, gas, artificial] return [[[PeriodicElements sharedPeriodicElements] elementPhysicalStatesArray] objectAtIndex:section]; } Indent a Row The code in Listing 4-12 moves a specific row to the next level of indentation. Listing 4-12 Custom indentation of a row - (NSInteger)tableView:(UITableView *)tableView indentationLevelForRowAtIndexPath:(NSIndexPath *)indexPath { if ( indexPath.section==TRAIL_MAP_SECTION && indexPath.row==0 ) { return 2; } return 1; } Creating and Configuring a Table View Optional Table View Configurations 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 53Vary a Row’s Height The example in Listing 4-13 varies the height of a specific row based on its index value. Listing 4-13 Varying row height - (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath { CGFloat result; switch ([indexPath row]) { case 0: { result = kUIRowHeight; break; } case 1: { result = kUIRowLabelHeight; break; } } return result; } Customize Cells You can also affect the appearance of rows by returning custom UITableViewCell objects with specially formatted subviews for content in tableView:cellForRowAtIndexPath:. Cell customization is discussed in “A Closer Look at Table View Cells” (page 55). Creating and Configuring a Table View Optional Table View Configurations 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 54A table view uses cell objects to draw its visible rows and then caches those objects as long as the rows are visible. Cells inherit from the UITableViewCell class. The table view’s data source provides the cell objects to the table view by implementing the tableView:cellForRowAtIndexPath: method, a required method of the UITableViewDataSource protocol. In this chapter, you’ll learn about: ● The characteristics of cells ● How to use the default capabilities of UITableViewCell for setting cell content ● How to create custom UITableViewCell objects Characteristics of Cell Objects A cell object has various parts, which can change depending on the mode of the table view. Normally, most of a cell object is reserved for its content: text, image, or any other kind of distinctive identifier. Figure 5-1 shows the major parts of a cell. Figure 5-1 Parts of a table view cell Cell content Accessory view The smaller area on the rightside of the cell isreserved for accessory views: disclosure indicators, detail disclosure controls, control objects such as sliders or switches, and custom views. 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 55 A Closer Look at Table View CellsWhen the table view goes into editing mode, the editing control for each cell object (if it’s configured to have such a control) appears on its left side, in the area shown in Figure 5-2. Figure 5-2 Parts of a table-view cell in editing mode Editing control Cell content Reordering control The editing control can be either a deletion control (a red minus sign inside a circle) or an insertion control (a green plus sign inside a circle). The cell’s content is pushed toward the right to make room for the editing control. If the cell object is configured for reordering (that is, relocation within the table view), the reordering control appearsin the rightside of the cell, next to any accessory view specified for editing mode. The reordering control is a stack of horizontal lines; to relocate a row within itstable view, users press on the reordering control and drag the cell. If a cell object isreusable—the typical case—you assign it a reuse identifier (an arbitrary string) in the storyboard. At runtime, the table view stores cell objects in an internal queue. When the table view asks the data source to configure a cell object for display, the data source can access the queued object by sending a dequeueReusableCellWithIdentifier: message to the table view, passing in a reuse identifier. The data source sets the content of the cell and any special properties before returning it. This reuse of cell objects is a performance enhancement because it eliminates the overhead of cell creation. With multiple cell objects in a queue, each with its own identifier, you can have table views constructed from cell objects of different types. For example, some rows of a table view can have content based on the image and text properties of a UITableViewCell in a predefined style, while other rows can be based on a customized UITableViewCell that defines a special format for its content. When providing cells for the table view, there are three general approaches you can take. You can use ready-made cell objects in a range of styles, you can add your own subviews to the cell object’s content view (which can be done in Interface Builder), or you can use cell objects created from a custom subclass of UITableViewCell. Note that the content view is a container of other views and so displays no content itself. A Closer Look at Table View Cells Characteristics of Cell Objects 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 56Using Cell Objects in Predefined Styles Using the UITableViewCell class directly, you can create “off-the-shelf” cell objects in a range of predefined styles. “Standard Styles for Table View Cells” (page 17) describes these standard cells and provides examples of how they look in a table view. These cells are associated with the following enum constants, declared in UITableViewCell.h: typedef enum { UITableViewCellStyleDefault, UITableViewCellStyleValue1, UITableViewCellStyleValue2, UITableViewCellStyleSubtitle } UITableViewCellStyle; These cell objects have two kinds of content: one or more text strings and, in some cases, an image. Figure 5-3 shows the approximate areas for image and text. As an image expands to the right, it pushes the text in the same direction. Figure 5-3 Default cell content in a UITableViewCell object Image Text Cell content Accessory view The UITableViewCell class defines three properties for this cell content: ● textLabel—A label for the title (a UILabel object) ● detailTextLabel—A label for the subtitle if there is additional detail (a UILabel object) ● imageView—An image view for an image (a UIImageView object) Because the first two of these properties are labels, you can set the font, alignment, line-break mode, and color of the associated text through the properties defined by the UILabel class (including the color of text when the row is highlighted). For the image view property, you can also set an alternative image for when the cell is highlighted using the highlightedImage property of the UIImageView class. A Closer Look at Table View Cells Using Cell Objects in Predefined Styles 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 57Figure 5-4 gives an example of a table view whose rows are drawn using a UITableViewCell object in the UITableViewCellStyleSubtitle style; it includes both an image and, for textual content, a title and a subtitle. Figure 5-4 A table view with rows showing both images and text Listing 5-1 showsthe implementation of tableView:cellForRowAtIndexPath: that createsthe table view rows in Figure 5-4 (page 58). The first thing the data source should do is send dequeueReusableCellWithIdentifier: to the table view, passing in a reuse identifier. If a prototype for the cell existsin a storyboard, the table view returns a reusable cell object. Then itsetsthe cell object’s content, both text and image. Listing 5-1 Configuring a UITableViewCell object with both image and text - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"MyIdentifier"]; if (cell == nil) { cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:@"MyIdentifier"]]; cell.selectionStyle = UITableViewCellSelectionStyleNone; } A Closer Look at Table View Cells Using Cell Objects in Predefined Styles 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 58NSDictionary *item = (NSDictionary *)[self.content objectAtIndex:indexPath.row]; cell.textLabel.text = [item objectForKey:@"mainTitleKey"]; cell.detailTextLabel.text = [item objectForKey:@"secondaryTitleKey"]; NSString *path = [[NSBundle mainBundle] pathForResource:[item objectForKey:@"imageKey"] ofType:@"png"]; UIImage *theImage = [UIImage imageWithContentsOfFile:path]; cell.imageView.image = theImage; return cell; } The table view’s data source implementation of tableView:cellForRowAtIndexPath: should always reset all content when reusing a cell. When you configure a UITableViewCell object, you can also set various other properties, including (but not limited to) the following: ● selectionStyle—Controls the appearance of the cell when selected. ● accessoryType and accessoryView—Allow you to set one of the standard accessory views(disclosure indicator or detail disclosure control) or a custom accessory view for a cell in normal (nonediting) mode. For a custom view, you may provide any UIView object, such as a slider, a switch, or a custom view. ● editingAccessoryType and editingAccessoryView—Allow you to set one of the standard accessory views (disclosure indicator or detail disclosure control) or a custom accessory view for a cell in editing mode. For a custom view, you may provide any UIView object, such as a slider, a switch, or a custom view. ● showsReorderControl—Specifies whether it shows a reordering control when in editing mode. The related but read-only editingStyle property specifies the type of editing control the cell has (if any). The delegate returns the value of the editingStyle property in its implementation of the tableView:editingStyleForRowAtIndexPath: method. ● backgroundView and selectedBackgroundView—Provide a background view (when a cell is unselected and selected) to display behind all other views of the cell. ● indentationLevel and indentationWidth—Specify the indentation level for cell content and the width of each indentation level. Because a table view cell inherits from UIView, you can also affect its appearance and behavior by setting the properties defined by that superclass. For example, to affect a cell’s background color, you could set its backgroundColor property. Listing 5-2 shows how you might use the delegate method tableView:willDisplayCell:forRowAtIndexPath: to alternate the background color of rows(via their backing cells) in a table view. A Closer Look at Table View Cells Using Cell Objects in Predefined Styles 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 59Listing 5-2 Alternating the background color of cells - (void)tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath { if (indexPath.row%2 == 0) { UIColor *altCellColor = [UIColor colorWithWhite:0.7 alpha:0.1]; cell.backgroundColor = altCellColor; } } Listing 5-2 also illustrates an important aspect of the table view API. A table view sends a tableView:willDisplayCell:forRowAtIndexPath: message to its delegate just before it draws a row. If the delegate chooses to implement this method, it can make last-minute changes to the cell object before it is displayed. With this method, the delegate should change only state-based properties that were set earlier by the table view, such as selection and background color, and not content. Customizing Cells The four predefined styles of UITableViewCell objects suffice for most of the rows that table views display. With these ready-made cell objects, rows can include one or two styles of text, often an image, and an accessory view of some sort. The application can modify the text in its font, color, and other characteristics, and it can supply an image for the row in its selected state as well as its normal state. Asflexible and useful asthis cell content is, it might notsatisfy the requirements of all applications. For example, the labels permitted by a native UITableViewCell object are pinned to specific locations within a row, and the image must appear on the left side of the row. If you want the cell to have different content components and to have these laid out in different locations, or if you want different behavioral characteristics for the cell, you have two alternatives: ● Add subviews to a cell’s content view. ● Create a custom subclass of UITableViewCell. The following sections discuss both approaches. A Closer Look at Table View Cells Customizing Cells 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 60Loading Table View Cells from a Storyboard In a storyboard, the cells in a table view are dynamic or static. With dynamic content, the table view is a list with a large (and potentially unbounded) number of rows. With static content, the number of rowsis a finite quantity that’s known at compile time. A table view that presents a detail view of an item is a good candidate for static content. You can design dynamic or static cell content directly inside a table view object. Figure 5-5 shows the master and detail table viewsin a simple storyboard. In this example, the master table view contains dynamic prototype cells, and the detail table view contains static cells. Figure 5-5 Table view cells in a storyboard The following sections demonstrate how to load data into table views that contain custom-configured cells. A Closer Look at Table View Cells Customizing Cells 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 61The Technique for Dynamic Row Content In this section, you compose a custom prototype cell in a storyboard. At runtime, the data source dequeues cells, prepares them, and gives them to its table view for drawing the rows depicted in Figure 5-6. Figure 5-6 Table view rows drawn with a custom prototype cell The data source can use two different ways to access the subviews of the cells. One approach uses the tag property defined by UIView and the other approach uses outlets. Using tags is convenient, although it makes the code more fragile because it introduces a coupling between the tag numbers in the storyboard and the code. Using outlets requires a little more work because you need to define a custom subclass of UITableViewCell. Both approaches are described here. To create a project that uses a storyboard to load custom table view cells 1. Create a project using the Master-Detail Application template and select the Use Storyboards option. 2. On the storyboard canvas, select the master view controller. 3. In the Identity inspector, verify that Class is set to the custom MasterViewController class. 4. Select the table view inside the master view controller. 5. In the Attributes inspector, verify that the Content pop-up menu is set to Dynamic Prototypes. 6. Select the prototype cell. 7. In the Attributes inspector, choose Custom in the Style pop-up menu. A Closer Look at Table View Cells Customizing Cells 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 628. Enter a reuse identifier in the Identifier text field. This is the same reuse identifier you send to the table view in the dequeueReusableCellWithIdentifier: message. For an example, see Listing 5-3. 9. Choose Disclosure Indicator in the Accessory pop-up menu. 10. Drag objects from the Library onto the cell. For this example, drag two label objects and position them near the ends of the cell (leaving room for the accessory view). 11. Select the objects and set their attributes, sizes, and autoresizing characteristics. An important attribute to set for the programmatic portion of this procedure is each object’s tag property. Find this property in the View section of the Attributes inspector and assign each object a unique integer. Now write the code you would normally write to obtain the table view’s data. (For this example, the only data you need is the row number of each cell.) Implement the data source method tableView:cellForRowAtIndexPath: to create a new cell from the prototype and populate it with data, in a manner similar to Listing 5-3. Listing 5-3 Adding data to a cell using tags - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"MyIdentifier"]; UILabel *label; label = (UILabel *)[cell viewWithTag:1]; label.text = [NSString stringWithFormat:@"%d", indexPath.row]; label = (UILabel *)[cell viewWithTag:2]; label.text = [NSString stringWithFormat:@"%d", NUMBER_OF_ROWS - indexPath.row]; return cell; } A Closer Look at Table View Cells Customizing Cells 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 63There are a few aspects of this code to note: ● The string identifier you assign to the prototype cell is the same string you pass to the table view in dequeueReusableCellWithIdentifier:. ● Because the prototype cell is defined in a storyboard, the dequeueReusableCellWithIdentifier: method always returns a valid cell. You don’t need to check the return value against nil and create a cell manually. ● The code gets the labels in the cell by calling viewWithTag:, passing in their tag integers. It can then set the textual content of the labels. If you prefer not to use tags, you can use an alternative method for setting the content in the cell. Define a custom UITableViewCell subclass with outlet properties for the objects you want to set. In the storyboard, associate the new class with the prototype cell and connect the outlets to the corresponding objects in the cell. To use outlets for the custom cell content 1. Add an Objective-C class named MyTableViewCell to your project. 2. Add the following code to the interface in MyTableViewCell.h: @interface MyTableViewCell : UITableViewCell @property (nonatomic, weak) IBOutlet UILabel *firstLabel; @property (nonatomic, weak) IBOutlet UILabel *secondLabel; @end 3. Add the following code to the implementation in MyTableViewCell.m: @synthesize firstLabel, secondLabel; 4. Add the following line of code to the source file that implements the data source: #import "MyTableViewCell.h" 5. Use the Identity inspector to set the Class of the prototype cell to MyTableViewCell. A Closer Look at Table View Cells Customizing Cells 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 646. Use the Connections inspector to connect the two outlets in the prototype cell to their corresponding labels. 7. Implement the data source method tableView:cellForRowAtIndexPath: in a manner similar to Listing 5-4. Listing 5-4 Adding data to a cell using outlets - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { MyTableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"MyIdentifier"]; cell.firstLabel.text = [NSString stringWithFormat:@"%d", indexPath.row]; cell.secondLabel.text = [NSString stringWithFormat:@"%d", NUMBER_OF_ROWS - indexPath.row]; return cell; } The code gains access to the labels in the cell using accessor methods (dot notation is used here). The code can then set the textual content of the labels. A Closer Look at Table View Cells Customizing Cells 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 65The Technique for Static Row Content In this section, you compose several cells in a table view with static content. At runtime, when the table view is loaded from the storyboard, the table view controller has immediate access to these cells and composes the sections and rows of the table view with them, as depicted in Figure 5-7. Figure 5-7 Table view rows drawn with multiple cells As with the procedure for dynamic content, start by adding a subclass of UITableViewController to your project. Define outlet properties for the master row label in the first cell and the slider value label in the last cell, as shown in Listing 5-5. Listing 5-5 Defining outlet properties for static cell objects @interface DetailViewController : UITableViewController @property (strong, nonatomic) id detailItem; @property (weak, nonatomic) IBOutlet UILabel *masterRowLabel; @property (weak, nonatomic) IBOutlet UILabel *sliderValueLabel; @property (weak, nonatomic) IBOutlet UISlider *slider; - (IBAction)logHello; - (IBAction)sliderValueChanged:(UISlider *)slider; A Closer Look at Table View Cells Customizing Cells 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 66@end In the storyboard, drag a Table View Controller object from the Library onto the canvas. Select the table view and set the following attributes in the Attributes inspector: 1. Set the Content pop-up menu to Static Cells. 2. Set the number of sections to 2. 3. Set the Style pop-up menu to Grouped. For each section in the table view, use the Attributes inspector to enter a string in the Header field. Then for the cells, complete the following steps: 1. Delete two of the three cells in the first table-view section and one cell in the second section. 2. Increase the height of each remaining cell as needed. It isn’t necessary to assign reuse identifiers tof these cells, because you’re not going to implement the data source method tableView:cellForRowAtIndexPath:. 3. Drag objects from the Library to compose the subviews of each cell as depicted in Figure 5-7 (page 66). 4. Set any desired attributes of these objects. The slider in this example has a range of values from 0 to 10 with an initial value of 7.5. A Closer Look at Table View Cells Customizing Cells 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 67Select the table view controller and display the Connections inspector. Make connections between the three outlets in your table view controller and the corresponding objects, as shown in Figure 5-8. While you’re at it, implement the two action methods declared in Listing 5-5 (page 66) and make target-action connections to the button and the slider. Figure 5-8 Making connections to your static cell content To populate the data in the static cells, implement a method called configureView in the detail view controller. In this example, detailItem is an NSString object passed in by the master view controller in its prepareForSegue:sender: method. The string contains the master row number. Listing 5-6 Setting the data in the user interface - (void)configureView { if (self.detailItem) { self.masterRowLabel.text = [self.detailItem description]; } self.sliderValueLabel.text = [NSString stringWithFormat:@"%1.1f", self.slider.value]; } A Closer Look at Table View Cells Customizing Cells 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 68The detail view controller calls the configureView method in viewDidLoad and setDetailItem:, as illustrated in the Xcode template Master-Detail Application. Programmatically Adding Subviews to a Cell’s Content View A cell that a table view uses for displaying a row is a view (UITableViewCell inherits from UIView). As a view, a cell has a content view—a superview for cell content—that it exposes as a property. To customize the appearance of rows in a table view, add subviews to the cell’s content view, which is accessible through its contentView property, and lay them out in the desired locations in their superview’s coordinates. You can configure and lay them out programmatically or in Interface Builder. (The approach using Interface Builder is discussed in “Loading Table View Cells from a Storyboard” (page 61).) One advantage of this approach is its relative simplicity; it doesn’t require you to create a custom subclass of UITableViewCell and handle all of the implementation details required for custom views. However, if you do take this approach, avoid making the views transparent, if you can. Transparent subviews affect scrolling performance because of the increased compositing cost. Subviews should be opaque, and typically should have the same background color as the cell. And if the cell is selectable, make sure that the cell content is highlighted appropriately when selected. The content is selected automatically if the subview implements (if appropriate) the accessor methods for the highlighted property. A Closer Look at Table View Cells Customizing Cells 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 69Suppose you want a cell with text and image content in custom locations. For example, you want the image on the right side of the cell and the title and subtitle of the cell right-aligned against the left side of the image. Figure 5-9 show how a table view with rows drawn with such a cell might look. (This example is for illustration only, and is not intended as a human-interface model.) Figure 5-9 Cells with custom content as subviews The code example in Listing 5-7 illustrates how the data source programmatically composes the cell with which thistable view drawsitsrows. In tableView:cellForRowAtIndexPath:, it first checksto see the table view already has a cell object with the given reuse identifier. If there is no such object, the data source creates two label objects and one image view with specific frames within the coordinate system of their superview (the content view). It also sets attributes of these objects. Having acquired an appropriate cell to use, the data source sets the cell’s content before returning the cell. Listing 5-7 Adding subviews to a cell’s content view #define MAINLABEL_TAG 1 #define SECONDLABEL_TAG 2 #define PHOTO_TAG 3 - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { A Closer Look at Table View Cells Customizing Cells 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 70static NSString *CellIdentifier = @"ImageOnRightCell"; UILabel *mainLabel, *secondLabel; UIImageView *photo; UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; if (cell == nil) { cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier]]; cell.accessoryType = UITableViewCellAccessoryDetailDisclosureButton; mainLabel = [[[UILabel alloc] initWithFrame:CGRectMake(0.0, 0.0, 220.0, 15.0)]]; mainLabel.tag = MAINLABEL_TAG; mainLabel.font = [UIFont systemFontOfSize:14.0]; mainLabel.textAlignment = UITextAlignmentRight; mainLabel.textColor = [UIColor blackColor]; mainLabel.autoresizingMask = UIViewAutoresizingFlexibleLeftMargin | UIViewAutoresizingFlexibleHeight; [cell.contentView addSubview:mainLabel]; secondLabel = [[[UILabel alloc] initWithFrame:CGRectMake(0.0, 20.0, 220.0, 25.0)]]; secondLabel.tag = SECONDLABEL_TAG; secondLabel.font = [UIFont systemFontOfSize:12.0]; secondLabel.textAlignment = UITextAlignmentRight; secondLabel.textColor = [UIColor darkGrayColor]; secondLabel.autoresizingMask = UIViewAutoresizingFlexibleLeftMargin | UIViewAutoresizingFlexibleHeight; [cell.contentView addSubview:secondLabel]; photo = [[[UIImageView alloc] initWithFrame:CGRectMake(225.0, 0.0, 80.0, 45.0)]]; photo.tag = PHOTO_TAG; photo.autoresizingMask = UIViewAutoresizingFlexibleLeftMargin | UIViewAutoresizingFlexibleHeight; [cell.contentView addSubview:photo]; } else { A Closer Look at Table View Cells Customizing Cells 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 71mainLabel = (UILabel *)[cell.contentView viewWithTag:MAINLABEL_TAG]; secondLabel = (UILabel *)[cell.contentView viewWithTag:SECONDLABEL_TAG]; photo = (UIImageView *)[cell.contentView viewWithTag:PHOTO_TAG]; } NSDictionary *aDict = [self.list objectAtIndex:indexPath.row]; mainLabel.text = [aDict objectForKey:@"mainTitleKey"]; secondLabel.text = [aDict objectForKey:@"secondaryTitleKey"]; NSString *imagePath = [[NSBundle mainBundle] pathForResource:[aDict objectForKey:@"imageKey"] ofType:@"png"]; UIImage *theImage = [UIImage imageWithContentsOfFile:imagePath]; photo.image = theImage; return cell; } When the data source creates the cells, it assigns each subview an identifier called a tag. With tags, you can locate a view in its view hierarchy by calling the viewWithTag: method. If the delegate later getsthe designated cell from the table view’s queue, it uses the tags to obtain references to the three subviews prior to assigning them content. This code creates a UITableViewCell object in the predefined default style (UITableViewCellStyleDefault). Because the content properties of the standard cells—textLabel, detailTextLabel, and imageView—are nil until assigned content, you may use any predefined cell as the template for customization. Note: Another approach is to subclass UITableViewCell and create instances in the UITableViewCellStyleSubtitle style. Then override the layoutSubviewsmethod to reposition the textLabel, detailTextLabel, and imageView subviews (after calling super). One way to achieve “attributed string” effects with textual content is to lay out UILabel subviews of the UITableViewCell content view. The text of each label can have its own font, color,size, alignment, and other characteristics. If you want that kind of variation within a label object, create multiple labels and lay them out relative to each other. A Closer Look at Table View Cells Customizing Cells 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 72Cells and Table View Performance The proper use of table view cells, whether off-the-shelf or custom cell objects, is a major factor in the performance of table views. Ensure that your application does the following three things: ● Reuse cells. Object allocation has a performance cost, especially if the allocation hasto happen repeatedly over a short period—say, when the user scrolls a table view. If you reuse cells instead of allocating new ones, you greatly enhance table view performance. ● Avoid relayout of content. When reusing cells with custom subviews, refrain from laying out those subviews each time the table view requests a cell. Lay out the subviews once, when the cell is created. ● Use opaque subviews. When customizing table view cells, make the subviews of the cell opaque, not transparent. A Closer Look at Table View Cells Cells and Table View Performance 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 73When users tap a row of a table view, usually something happens as a result. Another table view could slide into place, the row could display a checkmark, orsome other action could be performed. The following sections describe how to respond to selections and how to make selections programmatically. Selections in Table Views There are a few human-interface guidelines to keep in mind when dealing with cell selection in table views: ● You should never use selection to indicate state. Instead, use check marks and accessory viewsforshowing state. ● When the user selects a cell, you should respond by deselecting the previously selected cell (by calling the deselectRowAtIndexPath:animated: method) as well as by performing any appropriate action, such as displaying a detail view. ● If you respond to the the selection of a cell by pushing a new view controller onto the navigation controller’s stack, you should deselect the cell (with animation) when the view controller is popped off the stack. You can control whether rows are selectable when the table view is in editing mode by setting the allowsSelectionDuringEditing property of UITableView. In addition, beginning with iOS 3.0, you can control whether cells are selectable when editing mode is not in effect by setting the allowsSelection property. Responding to Selections Users tap a row in a table view either to signal to the application that they want to know more about what that row signifies or to select what the row represents. In response to the user tapping a row, an application could do any of the following: ● Show the next level in a data-model hierarchy. ● Show a detail view of an item (that is, a leaf node of the data-model hierarchy). ● Show a checkmark in the row to indicate that the represented item is selected. 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 74 Managing Selections● If the touch occurred in a control embedded in the row, it could respond to the action message sent by the control. To handle most selections of rows, the table view’s delegate must implement the tableView:didSelectRowAtIndexPath: method. In sample method implementation shown in Listing 6-1, the delegate first deselectsthe selected row. Then it allocates and initializes an instance of the next table-view controller in the sequence. Itsetsthe data this view controller needsto populate itstable view and then pushes this object onto the stack maintained by the application’s UINavigationController object. Listing 6-1 Responding to a row selection - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath { [tableView deselectRowAtIndexPath:indexPath animated:NO]; BATTrailsViewController *trailsController = [[BATTrailsViewController alloc] initWithStyle:UITableViewStylePlain]; trailsController.selectedRegion = [regions objectAtIndex:indexPath.row]; [[self navigationController] pushViewController:trailsController animated:YES]; [trailsController release]; } If a row has a disclosure control—the white chevron over a blue circle—for an accessory view, clicking the control resultsin the delegate receiving a tableView:accessoryButtonTappedForRowWithIndexPath: message (instead of tableView:didSelectRowAtIndexPath:). The delegate responds to this message in the same general way as it does for other kinds of selections. A row can also have a control object as its accessory view, such as a switch or a slider. This control object functions as it would in any other context: Manipulating the object in the proper way results in an action message being sent to a target object. Listing 6-2 illustrates a data source object that adds a UISwitch object as a cell’s accessory view and then responds to the action messages sent when the switch is “flipped.” Listing 6-2 Setting a switch object as an accessory view and responding to its action message - (UITableViewCell *)tableView:(UITableView *)tv cellForRowAtIndexPath:(NSIndexPath *)indexPath { UITableViewCell *cell = [tv dequeueReusableCellWithIdentifier:@"CellWithSwitch"]; if (cell == nil) { Managing Selections Responding to Selections 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 75cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:@"CellWithSwitch"] autorelease]; cell.selectionStyle = UITableViewCellSelectionStyleNone; cell.textLabel.font = [UIFont systemFontOfSize:14]; } UISwitch *switchObj = [[UISwitch alloc] initWithFrame:CGRectMake(1.0, 1.0, 20.0, 20.0)]; switchObj.on = YES; [switchObj addTarget:self action:@selector(toggleSoundEffects:) forControlEvents:(UIControlEventValueChanged | UIControlEventTouchDragInside)]; cell.accessoryView = switchObj; [switchObj release]; cell.textLabel.text = @"Sound Effects"; return cell; } - (void)toggleSoundEffects:(id)sender { [self.soundEffectsOn = [(UISwitch *)sender isOn]; [self reset]; } You may also define controls as accessory views of table-view cells created in Interface Builder. Drag a control object (switch, slider, and so on) into a nib document window containing a table-view cell. Then, using the connection window, make the control the accessory view of the cell. “Loading Table View Cells from a Storyboard” (page 61) describes the procedure for creating and configuring table-view cell objects in nib files. Selection management is also important with selection lists. There are two kinds of selection lists: ● Exclusive lists where only one row is permitted the checkmark ● Inclusive lists where more than one row can have a checkmark Listing 6-3 illustrates one approach to managing an exclusive selection list. It first deselects the currently selected row and returns if the same row is selected; otherwise it sets the checkmark accessory type on the newly selected row and removes the checkmark on the previously selected row Managing Selections Responding to Selections 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 76Listing 6-3 Managing a selection list—exclusive list - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath { [tableView deselectRowAtIndexPath:indexPath animated:NO]; NSInteger catIndex = [taskCategories indexOfObject:self.currentCategory]; if (catIndex == indexPath.row) { return; } NSIndexPath *oldIndexPath = [NSIndexPath indexPathForRow:catIndex inSection:0]; UITableViewCell *newCell = [tableView cellForRowAtIndexPath:indexPath]; if (newCell.accessoryType == UITableViewCellAccessoryNone) { newCell.accessoryType = UITableViewCellAccessoryCheckmark; self.currentCategory = [taskCategories objectAtIndex:indexPath.row]; } UITableViewCell *oldCell = [tableView cellForRowAtIndexPath:oldIndexPath]; if (oldCell.accessoryType == UITableViewCellAccessoryCheckmark) { oldCell.accessoryType = UITableViewCellAccessoryNone; } } Listing 6-4 illustrates how to manage a inclusive selection list. As the comments in this example indicate, when the delegate adds a checkmark to a row or removes one, it typically also sets or unsets any associated model-object attribute. Listing 6-4 Managing a selection list—inclusive list - (void)tableView:(UITableView *)theTableView didSelectRowAtIndexPath:(NSIndexPath *)newIndexPath { [theTableView deselectRowAtIndexPath:[theTableView indexPathForSelectedRow] animated:NO]; UITableViewCell *cell = [theTableView cellForRowAtIndexPath:newIndexPath]; if (cell.accessoryType == UITableViewCellAccessoryNone) { cell.accessoryType = UITableViewCellAccessoryCheckmark; Managing Selections Responding to Selections 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 77// Reflect selection in data model } else if (cell.accessoryType == UITableViewCellAccessoryCheckmark) { cell.accessoryType = UITableViewCellAccessoryNone; // Reflect deselection in data model } } In tableView:didSelectRowAtIndexPath: you should always deselect the currently selected row. Programmatically Selecting and Scrolling Occasionally the selection of a row originates within the application itself rather than from a tap in a table view. There could be an externally induced change in the data model. For example, the user adds a new person to an address book and then returnsto the list of contacts; the application wantsto scroll thislist to the recently added person. For situations like these, you can use the UITableView methods selectRowAtIndexPath:animated:scrollPosition: and (if the row is already selected) scrollToNearestSelectedRowAtScrollPosition:animated:. You may also call scrollToRowAtIndexPath:atScrollPosition:animated: if you want to scroll to a specific row without selecting it. The code in Listing 6-5 (somewhat whimsically) programmatically selects and scrolls to a row 20 rows away from the just-selected row using the selectRowAtIndexPath:animated:scrollPosition: method. Listing 6-5 Programmatically selecting a row - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)newIndexPath { NSIndexPath *scrollIndexPath; if (newIndexPath.row + 20 < [timeZoneNames count]) { scrollIndexPath = [NSIndexPath indexPathForRow:newIndexPath.row+20 inSection:newIndexPath.section]; } else { scrollIndexPath = [NSIndexPath indexPathForRow:newIndexPath.row-20 inSection:newIndexPath.section]; } [theTableView selectRowAtIndexPath:scrollIndexPath animated:YES scrollPosition:UITableViewScrollPositionMiddle]; Managing Selections Programmatically Selecting and Scrolling 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 78} Managing Selections Programmatically Selecting and Scrolling 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 79A table view has an editing mode as well as its normal (selection) mode. When a table view goes into editing mode, it displays the editing and reordering controls associated with its rows. The editing controls, which are in the left side of the row, allow the user to insert and delete rows in the table view. The editing controls have distinctive appearances: Deletion control Insertion control When a table view enters editing mode and when users click an editing control, the table view sends a series of messages to its data source and delegate, but only if they implement these methods. These methods allow the data source and delegate to refine the appearance and behavior of rows in the table view; the messages also enable them to carry out the deletion or insertion operation. Even if a table view is not in editing mode, you can insert or delete a number of rows or sections as a group and have those operations animated. The first section below shows you how, when a table is in editing mode, to insert new rows and delete existing rows in a table view in response to user actions. The second section, “Batch Insertion, Deletion, and Reloading of Rows and Sections” (page 87), discusses how you can insert and delete multiple sections and rows animated as a group. 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 80 Inserting and Deleting Rows and SectionsNote: The procedure for reordering rows when in editing mode is described in “Managing the Reordering of Rows” (page 91). Inserting and Deleting Rows in Editing Mode When a Table View is Edited A table view goes into editing mode when it receives a setEditing:animated: message. Typically (but not necessarily) the message originates as an action message sent when the user taps an Edit button in the navigation bar. In editing mode, a table view displays any editing (and reordering) controls that its delegate has assigned to each row. The delegate assigns the controls as a result of returning the editing style for a row in the tableView:editingStyleForRowAtIndexPath: method. Inserting and Deleting Rows and Sections Inserting and Deleting Rows in Editing Mode 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 81Note: If a UIViewController object is managing the table view, it automatically receives a setEditing:animated: message when the Edit button is tapped. In its implementation of this message, it can update button state or do any other kind of task before invoking the table view’s version of the method. When the table view receives setEditing:animated:, itsendsthe same message to the UITableViewCell object for each visible row. Then it sends a succession of messages to its data source and its delegate (if they implement the methods) as depicted in the diagram in Figure 7-1. Figure 7-1 Calling sequence for inserting or deleting rows in a table view tableView: editingStyleForRowAtIndexPath: tableView: canEditRowAtIndexPath: Client Delegate Data Source Table View User presses Edit button User presses editing control User presses Delete button setEditing:YES animated:YES tableView:commitEditingStyle: forRowAtIndexPath: deleteRowsAtIndexPath: withRowAnimation or insertRowsAtIndexPath: withRowAnimation: After resending setEditing:animated: to the cells corresponding to the visible rows, the sequence of messages is as follows: 1. The table view invokesthe tableView:canEditRowAtIndexPath: method if its data source implements it. This method allows the application to exclude rows in the table view from being edited even when their cell’s editingStyle property indicates otherwise. Most applications do not need to implement this method. 2. The table view invokes the tableView:editingStyleForRowAtIndexPath: method if its delegate implements it. This method allows the application to specify a row’s editing style and thus the editing control that the row displays. Inserting and Deleting Rows and Sections Inserting and Deleting Rows in Editing Mode 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 82At this point, the table view is fully in editing mode. It displays the insertion or deletion control for each eligible row. 3. The user taps an editing control (either the deletion control or the insertion control). If he or she taps a deletion control, a Delete button is displayed on the row. The user then taps that button to confirm the deletion. 4. The table view sends the tableView:commitEditingStyle:forRowAtIndexPath: message to the data source. Although this protocol method is marked as optional, the data source must implement it if it wants to insert or delete a row. It must do two things: ● Send deleteRowsAtIndexPaths:withRowAnimation: or insertRowsAtIndexPaths:withRowAnimation: to the table view to direct it to adjust its presentation. ● Update the corresponding data-model array by either deleting the referenced item from the array or adding an item to the array. When the user swipes across a row to display the Delete button for that row, there is a variation in the calling sequence diagrammed in Figure 7-1 (page 82). When the user swipes a row to delete it, the table view first checks to see if its data source has implemented the tableView:commitEditingStyle:forRowAtIndexPath: method; if that is so, it sends setEditing:animated: to itself and enters editing mode. In this “swipe to delete” mode, the table view does not display the editing and reordering controls. Because this is a user-driven event, it also brackets the messagesto the delegate inside of two other messages: tableView:willBeginEditingRowAtIndexPath: and tableView:didEndEditingRowAtIndexPath:. By implementing these methods, the delegate can update the appearance of the table view appropriately. Note: The data source should not call setEditing:animated: from within its implementation of tableView:commitEditingStyle:forRowAtIndexPath:. If forsome reason it must, itshould invoke it after a delay by using the performSelector:withObject:afterDelay: method. Although you can use an insertion control as the trigger to insert a new row in a table view, an alternative approach is to have an Add (or plus sign) button in the navigation bar. Tapping the button sends an action message to the view controller, which overlays the table view with a modal view for entering the new item. Once the item is entered, the controller adds it to the data-model array and reloads the table. “An Example of Adding a Table-View Row” (page 85) discusses this approach. Inserting and Deleting Rows and Sections Inserting and Deleting Rows in Editing Mode 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 83An Example of Deleting a Table-View Row This section gives a guided tour through the parts of a project that work together to set up a table view for editing mode and delete rowsfrom it. This project usesthe navigation controller and view controller architecture to manage its table views. In its loadView method, the custom view controller creates the table view and sets itself to be the data source and delegate. It also sets the right item of the navigation bar to be the standard Edit button. self.navigationItem.rightBarButtonItem = self.editButtonItem; This button is preconfigured to send setEditing:animated: to the view controller when tapped; it toggles the button title (between Edit and Done) and the Boolean editing parameter on alternating taps. In its implementation of the method, as shown in Listing 7-1, the view controller invokes the superclass invocation of the method, sends the same message to the table view, and updates the enabled state of the other button in the navigation bar (a plus-sign button, for adding items). Listing 7-1 View controller responding to setEditing:animated: - (void)setEditing:(BOOL)editing animated:(BOOL)animated { [super setEditing:editing animated:animated]; [tableView setEditing:editing animated:YES]; if (editing) { addButton.enabled = NO; } else { addButton.enabled = YES; } } When its table view enters editing mode, the view controller specifies a deletion control for every row except the last, which has an insertion control. It does this in its implementation of the tableView:editingStyleForRowAtIndexPath: method (Listing 7-2). Listing 7-2 Customizing the editing style of rows - (UITableViewCellEditingStyle)tableView:(UITableView *)tableView editingStyleForRowAtIndexPath:(NSIndexPath *)indexPath { SimpleEditableListAppDelegate *controller = (SimpleEditableListAppDelegate *)[[UIApplication sharedApplication] delegate]; if (indexPath.row == [controller countOfList]-1) { Inserting and Deleting Rows and Sections Inserting and Deleting Rows in Editing Mode 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 84return UITableViewCellEditingStyleInsert; } else { return UITableViewCellEditingStyleDelete; } } The user taps the deletion control in a row and the view controller receives a tableView:commitEditingStyle:forRowAtIndexPath: message from the table view. As shown in Listing 7-3, it handles this message by removing the item corresponding to the row from a model array and sending deleteRowsAtIndexPaths:withRowAnimation: to the table view. Listing 7-3 Updating the data-model array and deleting the row - (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath { // If row is deleted, remove it from the list. if (editingStyle == UITableViewCellEditingStyleDelete) { SimpleEditableListAppDelegate *controller = (SimpleEditableListAppDelegate *)[[UIApplication sharedApplication] delegate]; [controller removeObjectFromListAtIndex:indexPath.row]; [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade]; } } An Example of Adding a Table-View Row This section shows project code that inserts a row in a table view. Instead of using the insertion control as the trigger for inserting a row, it uses an Add button (visually a plus sign) in the navigation bar above the table view. This code also is based on the navigation controller and view controller architecture. In its loadView method implementation, the view controller assigns the Add button as the right-side item of the navigation bar using the code shown in Listing 7-4. Listing 7-4 Adding an Add button to the navigation bar addButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:self action:@selector(addItem:)]; Inserting and Deleting Rows and Sections Inserting and Deleting Rows in Editing Mode 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 85self.navigationItem.rightBarButtonItem = addButton; Note that the view controller sets the control states for the title as well as the action selector and the target object. When the user taps the Add button, the addItem: message is sent to the target (the view controller). It responds as shown in Listing 7-5. It creates a navigation controller with a single view controller whose view is put onscreen modally—it animates upward to overlay the table view. The presentModalViewController:animated: method to do this. Listing 7-5 Responding to a tap on the Add button - (void)addItem:sender { if (itemInputController == nil) { itemInputController = [[ItemInputController alloc] init]; } UINavigationController *navigationController = [[UINavigationController alloc] initWithRootViewController:itemInputController]; [[self navigationController] presentModalViewController:navigationController animated:YES]; [navigationController release]; } The modal, or overlay, view consists of a single custom text field. The user enters text for the new table-view item and then taps a Save button. This button sends a save: action message to its target: the view controller for the modal view. As shown in Listing 7-6, the view controller extracts the string value from the text field and updates the application’s data-model array with it. Listing 7-6 Adding the new item to the data-model array - (void)save:sender { UITextField *textField = [(EditableTableViewTextField *)[tableView cellForRowAtIndexPath:[NSIndexPath indexPathForRow:0 inSection:0]] textField]; SimpleEditableListAppDelegate *controller = (SimpleEditableListAppDelegate *)[[UIApplication sharedApplication] delegate]; NSString *newItem = textField.text; if (newItem != nil) { [controller insertObject:newItem inListAtIndex:[controller countOfList]]; Inserting and Deleting Rows and Sections Inserting and Deleting Rows in Editing Mode 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 86} [self dismissModalViewControllerAnimated:YES]; } After the modal view is dismissed the table view is reloaded, and it now reflects the added item. Batch Insertion, Deletion, and Reloading of Rows and Sections The UITableView class allows you to insert, delete, and reload a group of rows or sections at one time, animating the operations simultaneously in specified ways. The eight methods shown in Listing 7-7 pertain to batch insertion and deletion. Note that you can call these insertion and deletion methods outside of an animation block (as you do in the data source method tableView:commitEditingStyle:forRowAtIndexPath: as discussed in “Inserting and Deleting Rows in Editing Mode” (page 81)). Listing 7-7 Batch insertion and deletion methods - (void)beginUpdates; - (void)endUpdates; - (void)insertSections:(NSIndexSet *)sections withRowAnimation:(UITableViewRowAnimation)animation; - (void)deleteSections:(NSIndexSet *)sections withRowAnimation:(UITableViewRowAnimation)animation; - (void)reloadSections:(NSIndexSet *)sections withRowAnimation:(UITableViewRowAnimation)animation; - (void)insertRowsAtIndexPaths:(NSArray *)indexPaths withRowAnimation: (UITableViewRowAnimation)animation; - (void)deleteRowsAtIndexPaths:(NSArray *)indexPaths withRowAnimation: (UITableViewRowAnimation)animation; - (void)reloadRowsAtIndexPaths:(NSArray *)indexPaths withRowAnimation:(UITableViewRowAnimation)animation; Inserting and Deleting Rows and Sections Batch Insertion, Deletion, and Reloading of Rows and Sections 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 87Note: The reloadSections:withRowAnimation: and reloadRowsAtIndexPaths:withRowAnimation: methods, which were introduced in iOS 3.0, allow you to request the table view to reload the data for specific sections and rows instead of loading the entire visible table view by calling reloadData. To animate a batch insertion, deletion, and reloading of rows and sections, call the corresponding methods within an animation block defined by successive calls to beginUpdates and endUpdates. If you don’t call the insertion, deletion, and reloading methods within this block, row and section indexes may be invalid. Calls to beginUpdates and endUpdates can be nested; all indexes are treated as if there were only the outer update block. At the conclusion of a block—that is, after endUpdates returns—the table view queries its data source and delegate as usual for row and section data. Thusthe collection objects backing the table view should be updated to reflect the new or removed rows or sections. An Example of Batched Insertion and Deletion Operations To insert and delete a group of rows and sections in a table view, first prepare the array (or arrays) that are the source of data for the sections and rows. After rows and sections are deleted and inserted, the resulting rows and sections are populated from this data store. Next, call the beginUpdates method, followed by invocations of insertRowsAtIndexPaths:withRowAnimation:, deleteRowsAtIndexPaths:withRowAnimation:, insertSections:withRowAnimation:, or deleteSections:withRowAnimation:. Conclude the animation block by calling endUpdates. Listing 7-8 illustrates this procedure. Listing 7-8 Inserting and deleting a block of rows in a table view - (IBAction)insertAndDeleteRows:(id)sender { // original rows: Arizona, California, Delaware, New Jersey, Washington [states removeObjectAtIndex:4]; // Washington [states removeObjectAtIndex:2]; // Delaware [states insertObject:@"Alaska" atIndex:0]; [states insertObject:@"Georgia" atIndex:3]; [states insertObject:@"Virginia" atIndex:5]; NSArray *deleteIndexPaths = [NSArray arrayWithObjects: Inserting and Deleting Rows and Sections Batch Insertion, Deletion, and Reloading of Rows and Sections 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 88[NSIndexPath indexPathForRow:2 inSection:0], [NSIndexPath indexPathForRow:4 inSection:0], nil]; NSArray *insertIndexPaths = [NSArray arrayWithObjects: [NSIndexPath indexPathForRow:0 inSection:0], [NSIndexPath indexPathForRow:3 inSection:0], [NSIndexPath indexPathForRow:5 inSection:0], nil]; UITableView *tv = (UITableView *)self.view; [tv beginUpdates]; [tv insertRowsAtIndexPaths:insertIndexPaths withRowAnimation:UITableViewRowAnimationRight]; [tv deleteRowsAtIndexPaths:deleteIndexPaths withRowAnimation:UITableViewRowAnimationFade]; [tv endUpdates]; // ending rows: Alaska, Arizona, California, Georgia, New Jersey, Virginia } This example removes two strings from an array (and their corresponding rows) and inserts three strings into the array (along with their corresponding rows). The next section, “Ordering of Operations and Index Paths,” explains particular aspects of the row (or section) insertion and deletion behavior. Ordering of Operations and Index Paths You might have noticed something in the code shown in Listing 7-8 that seems peculiar. The code calls the deleteRowsAtIndexPaths:withRowAnimation: method after it calls insertRowsAtIndexPaths:withRowAnimation:. However, this is not the order in which UITableView completes the operations. It defers any insertions of rows or sections until after it has handled the deletions of rows or sections. The table view behaves the same way with reloading methods called inside an update block—the reload takes place with respect to the indexes of rows and sections before the animation block is executed. This behavior happens regardless of the ordering of the insertion, deletion, and reloading method calls. Deletion and reloading operations within an animation block specify which rows and sections in the original table should be removed or reloaded; insertions specify which rows and sections should be added to the resulting table. The index paths used to identify sections and rows follow this model. Inserting or removing Inserting and Deleting Rows and Sections Batch Insertion, Deletion, and Reloading of Rows and Sections 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 89an item in a mutable array, on the other hand, may affect the array index used for the successive insertion or removal operation; for example, if you insert an item at a certain index, the indexes of all subsequent items in the array are incremented. An example is useful here. Say you have a table view with three sections, each with three rows. Then you implement the following animation block: 1. Begin updates. 2. Delete row at index 1 of section at index 0. 3. Delete section at index 1. 4. Insert row at index 1 of section at index 1. 5. End updates. Figure 7-2 illustrates what takes place after the animation block concludes. Figure 7-2 Deletion of section and row and insertion of row Section 1 Section 0 Section 1 Section 2 Section 0 0 New 1 2 0 1 2 0 1 2 3 0 1 0 1 2 x X Inserting and Deleting Rows and Sections Batch Insertion, Deletion, and Reloading of Rows and Sections 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 90A table view has an editing mode as well as its normal (selection) mode. When a table view goes into editing mode, it displays the editing and reordering controls associated with its rows. The reordering control allows the user to move a row to a different location in the table. As shown in Figure 8-1, the reordering control appears on the right side of the row. Figure 8-1 Reordering a row When a table view enters editing mode and when users drag a reordering control, the table view sends a series of messages to its data source and delegate, but only if they implement these methods. These methods allow the data source and delegate to restrict whether and where a row can be moved as well to carry out the actual move operation. The following sections show you how to move rows around in a table view. 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 91 Managing the Reordering of RowsWhat Happens When a Row is Relocated A table view goes into editing mode when it receives a setEditing:animated: message. Typically (but not necessarily) the message originates as an action message sent when the user taps an Edit button in the navigation bar. In editing mode, a table view displays any reordering (and editing) controls that its delegate has assigned to each row. The delegate assigns the controls in tableView:cellForRowAtIndexPath: by setting the showsReorderControl property of UITableViewCell objects to YES. Note: If a UIViewController object is managing the table view, it automatically receives a setEditing:animated: message when the Edit button is tapped. UITableViewController, a subclass of UIViewController, implements this method to update button state and invoke the table view’s version of the method. If you are using UIViewController to manage a table view, you need to implement the same behavior. When the table view receives setEditing:animated:, itsendsthe same message to the UITableViewCell object for each visible row. Then it sends a succession of messages to its data source and its delegate (if they implement the methods) as depicted in the diagram in Figure 8-2. Figure 8-2 Calling sequence for reordering a row in a table view tableView: canMoveRowAtIndexPath: Client Delegate Data Source Table View User presses Edit button User drags reordering control setEditing:YES animated:YES tableView: moveRowAtIndexPath: toRowAtIndexPath: tableView: targetIndexPathForMoveFromRowAtIndexPath: toProposedIndexPath: When the table view receives the setEditing:animated: message, it resends the same message to the cell objects corresponding to its visible rows. After that, the sequence of messages is as follows: Managing the Reordering of Rows What Happens When a Row is Relocated 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 921. The table view sends a tableView:canMoveRowAtIndexPath: message to its data source (if it implements the method). In this method the delegate may selectively exclude certain rows from showing the reordering control. 2. The user drags a row by its reordering control up or down the table view. As the dragged row hovers over a part of the table view, the underlying row slides downward to show where the destination would be. 3. Every time the dragged row is over a destination, the table view sends tableView:targetIndexPathForMoveFromRowAtIndexPath:toProposedIndexPath: to its delegate (if it implements the method). In this method the delegate may reject the current destination for the dragged row and specify an alternative one. 4. The table view sends tableView:moveRowAtIndexPath:toIndexPath: to its data source (if it implements the method). In this method the data source updates the data-model array that is the source of items for the table view, moving the item to a different location in the array. Examples of Moving a Row Thissection comments on some sample code that illustratesthe reordering steps enumerated in “What Happens When a Row is Relocated” (page 92). Listing 8-1 shows an implementation of tableView:canMoveRowAtIndexPath: that excludes the first row in the table view from being reordered (this row does not have a reordering control). Listing 8-1 Excluding a row from relocation - (BOOL)tableView:(UITableView *)tableView canMoveRowAtIndexPath:(NSIndexPath *)indexPath { if (indexPath.row == 0) // Don't move the first row return NO; return YES; } When the user finishes dragging a row, it slides into its destination in the table view, which sends tableView:moveRowAtIndexPath:toIndexPath: to its data source. Listing 8-2 shows an implementation of this method. Note that it retains the data item fetched from the array (the item to be relocated) because the item is automatically released when it is removed from the array. Managing the Reordering of Rows Examples of Moving a Row 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 93Listing 8-2 Updating the data-model array for the relocated row - (void)tableView:(UITableView *)tableView moveRowAtIndexPath:(NSIndexPath *)sourceIndexPath toIndexPath:(NSIndexPath *)destinationIndexPath { NSString *stringToMove = [[self.reorderingRows objectAtIndex:sourceIndexPath.row] retain]; [self.reorderingRows removeObjectAtIndex:sourceIndexPath.row]; [self.reorderingRows insertObject:stringToMove atIndex:destinationIndexPath.row]; [stringToMove release]; } The delegate can also retarget the proposed destination for a move to another row by implementing the tableView:targetIndexPathForMoveFromRowAtIndexPath:toProposedIndexPath: method. The following example restricts rows to relocation in their own group and prevents moves to the last row of a group (which is reserved for the add-item placeholder). Listing 8-3 Retargeting the destination row of a move operation - (NSIndexPath *)tableView:(UITableView *)tableView targetIndexPathForMoveFromRowAtIndexPath:(NSIndexPath *)sourceIndexPath toProposedIndexPath:(NSIndexPath *)proposedDestinationIndexPath { NSDictionary *section = [data objectAtIndex:sourceIndexPath.section]; NSUInteger sectionCount = [[section valueForKey:@"content"] count]; if (sourceIndexPath.section != proposedDestinationIndexPath.section) { NSUInteger rowInSourceSection = (sourceIndexPath.section > proposedDestinationIndexPath.section) ? 0 : sectionCount - 1; return [NSIndexPath indexPathForRow:rowInSourceSection inSection:sourceIndexPath.section]; } else if (proposedDestinationIndexPath.row >= sectionCount) { return [NSIndexPath indexPathForRow:sectionCount - 1 inSection:sourceIndexPath.section]; } // Allow the proposed destination. return proposedDestinationIndexPath; } Managing the Reordering of Rows Examples of Moving a Row 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 94This table describes the changes to Table View Programming Guide for iOS . Date Notes 2012-09-19 Added new information for iOS 5. 2011-01-05 Made some minor corrections. 2010-09-14 Made several minor corrections. 2010-08-03 States now that beginUpdates...endUpdates calls can be nested. 2010-07-08 Changed the title from "Table View Programming Guide for iPhone OS." Made many minor corrections in diagrams and text. Added description of reload behavior in batch udpates. 2010-05-20 2010-03-24 Made the introduction more informative. Explained how to set the background color of cells, emphasized purpose of tableView:willDisplayCell:forRowAtIndexPath:, and made minor corrections. 2009-08-19 Updated to describe 3.0 API, especially predefined cell styles and related properties. It also describes the use of nib files with table views and table-view cells and includes an updated chapter on view controllers and design patterns and strategies. 2009-05-28 Warned against calling setEditing:animated: when in tableView:commitEditingStyle:forRowAtIndexPath:. Updated illustration. 2008-10-15 Added section on batch insertions and deletions, added related classes to TOC frame, added guidelines on clearing selection, and made minor corrections. 2008-09-09 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 95 Document Revision HistoryDate Notes 2008-06-25 First version of this document. Document Revision History 2012-09-19 | © 2012 Apple Inc. All Rights Reserved. 96Apple Inc. © 2012 Apple Inc. All rights reserved. No part of this publication may be reproduced, stored in a retrievalsystem, or transmitted, in any form or by any means, mechanical, electronic, photocopying, recording, or otherwise, without prior written permission of Apple Inc., with the following exceptions: Any person is hereby authorized to store documentation on a single computer for personal use only and to print copies of documentation for personal use provided that the documentation contains Apple’s copyright notice. No licenses, express or implied, are granted with respect to any of the technology described in this document. Apple retains all intellectual property rights associated with the technology described in this document. This document is intended to assist application developers to develop applications only for Apple-labeled computers. Apple Inc. 1 Infinite Loop Cupertino, CA 95014 408-996-1010 Apple, the Apple logo, Cocoa, Cocoa Touch, iPad, iPhone, Objective-C, and Xcode are trademarks of Apple Inc., registered in the U.S. and other countries. iOS is a trademark or registered trademark of Cisco in the U.S. and other countries and is used under license. Even though Apple has reviewed this document, APPLE MAKES NO WARRANTY OR REPRESENTATION, EITHER EXPRESS OR IMPLIED, WITH RESPECT TO THIS DOCUMENT, ITS QUALITY, ACCURACY, MERCHANTABILITY, OR FITNESS FOR A PARTICULAR PURPOSE.ASARESULT, THISDOCUMENT IS PROVIDED “AS IS,” AND YOU, THE READER, ARE ASSUMING THE ENTIRE RISK AS TO ITS QUALITY AND ACCURACY. IN NO EVENT WILL APPLE BE LIABLE FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL,OR CONSEQUENTIAL DAMAGES RESULTING FROM ANY DEFECT OR INACCURACY IN THIS DOCUMENT, even if advised of the possibility of such damages. THE WARRANTY AND REMEDIES SET FORTH ABOVE ARE EXCLUSIVE AND IN LIEU OF ALL OTHERS, ORAL OR WRITTEN, EXPRESS OR IMPLIED. No Apple dealer, agent, or employee is authorized to make any modification, extension, or addition to this warranty. Some states do not allow the exclusion or limitation of implied warranties or liability for incidental or consequential damages, so the above limitation or exclusion may not apply to you. This warranty gives you specific legal rights, and you may also have other rights which vary from state to state. TableView_iPhone.pdf Deux doigts d’astuces Démarrage Requiert un appareil compatible FaceTime et une connexion Wi-Fi, pour l’appelant comme pour l’appelé. Non disponible partout Bienvenue dans l’univers iPhone. Ce guide de démarrage rapide vous présente comment configurer votre iPhone et utiliser ses fonctionnalités principales. Une fois prêt à profiter de votre iPhone, vous pouvez obtenir des renseignements plus détaillés sur www.apple.com/fr/iphone ou www.apple.com/iphone/countries. À vos marques, configurez, partez ! 1. Téléchargement d’iTunes. Rendez-vous sur www.itunes.com/fr/download et téléchargez la dernière version d’iTunes à installer sur votre Mac ou PC. 2. Connexion à votre ordinateur. Connectez votre iPhone au port USB de votre ordinateur. 3. Synchronisation. Lorsque l’iPhone est connecté, iTunes s’ouvre et vous guide dans l’installation. Sélectionnez les contacts, les calendriers, la musique, les vidéos et les photos que vous souhaitez synchroniser, puis cliquez sur Appliquer dans l’angle droit inférieur. Si vous n’avez jamais utilisé iTunes ou que vous souhaitez vous informer sur la synchronisation, vous pouvez consulter un guide d’initiation rapide sur www.apple.com/fr/itunes/tutorials. Bouton Marche/Veille. Pour allumer l’iPhone, appuyez fermement sur le bouton Marche/Veille. Pour l’éteindre ou le redémarrer, maintenez le bouton Marche/Veille enfoncé pendant quelques secondes, puis faites glisser le curseur pour confirmer. Pour mettre l’iPhone en mode veille, appuyez une fois sur le bouton Marche/Veille, ce qui a pour effet d’éteindre l’écran tout en permettant à l’iPhone de recevoir des appels. Pour mettre en silence un appel entrant, appuyez une fois sur ce bouton. Pour envoyer un appel directement vers la messagerie vocale, appuyez deux fois dessus. Accueil. Lorsque vous utilisez une application, appuyez sur le bouton principal pour fermer celle-ci et revenir à son écran d’accueil. Pour accéder rapidement à l’écran d’accueil principal, appuyez sur le bouton principal depuis n’importe quel autre écran d’accueil. À partir de l’écran de verrouillage, double-cliquez sur le bouton d’accueil pour faire apparaître les commandes iPod. Créer des dossiers. Organiser ses applications. Touchez une icône et maintenez le doigt dessus jusqu’à ce qu’elle s’agite. Faites ensuite glisser une icône sur une autre afin de créer un dossier. Les dossiers sont nommés automatiquement par catégorie mais vous pouvez les renommer. Vous pouvez personnaliser votre écran d’accueil en faisant glisser des icônes et dossiers à différents emplacements et sur différents écrans. Une fois que vous avez terminé, il vous suffit d’appuyer sur le bouton principal. Rechercher. Pour effectuer une recherche sur votre iPhone ou sur le Web, allez à l’écran d’accueil et appuyez sur le bouton principal, ou passez le doigt sur l’écran de gauche à droite. Saisissez ce que vous souhaitez rechercher : un nom, une application, un morceau, un artiste, un film ou un mot-clé. L’iPhone propose des suggestions au fur et à mesure que vous écrivez, pour accélérer encore davantage votre recherche. Pour lancer une recherche depuis une application comme Mail, Contacts, Messages ou iPod, touchez la barre d’état. Effectuer un appel. Pour effectuer un appel, touchez un numéro de téléphone dans Contacts, Favoris, un courrier électronique, un SMS ou MMS, ou pratiquement n’importe où sur l’iPhone. Vous pouvez sinon toucher le bouton du clavier numérique afin de composer un numéro manuellement. Pour répondre à un appel alors que vous utilisez les écouteurs de l’iPhone, appuyez une fois sur le bouton central. Appuyez à nouveau dessus pour mettre fin à l’appel. Pour régler le volume, appuyez sur les boutons « + » et « - » situés au-dessus et en dessous du micro. FaceTime. Pour lancer une vidéoconférence lors d’un appel vocal, touchez le bouton FaceTime. Vous pouvez par ailleurs toucher le bouton FaceTime depuis l’application Contacts. Lors d’une vidéoconférence, vous pouvez activer la caméra de derrière et filmer ainsi autour de vous. Pour accéder à votre courrier électronique, Internet ou d’autres applications, appuyez sur le bouton principal. Multitâche. Pendant un appel, vous pouvez accéder à votre courrier électronique, à votre calendrier ou aux autres applications, et même naviguer sur le Web, dans la mesure où vous êtes connecté via Wi-Fi ou 3G. Pour passer rapidement d’une application à l’autre, appuyez deux fois sur le bouton principal pour afficher la liste des applications récemment utilisées. Faites défiler vers la droite pour voir plus d’applications, puis touchez une icône pour relancer l’application correspondante. Faites défiler vers la gauche jusqu’au bout pour accéder aux contrôles de l’iPod ou verrouiller l’orientation de l’écran. Contrôle vocal. Utilisez la fonction de contrôle vocal pour effectuer un appel ou écouter de la musique tout en gardant les mains libres. Pour activer cette fonction, maintenez enfoncé le bouton principal de l’iPhone ou le bouton central des écouteurs jusqu’à ce que l’écran du contrôle vocal apparaisse. Après la tonalité, énoncez une commande telle que « Appeler Emmanuelle » ou « Composer le 06 62 12 98 54 » en épelant chaque chiffre. Vous pouvez aussi demander à l’iPhone de jouer un album spécifique, un artiste ou une liste de lecture ou de « Jouer d’autres titres comme celui-ci ». Vous pouvez même demander à l’iPhone « Quel est ce morceau ? » ou encore « Écouter des morceaux des Rolling Stones ». Sonnerie/ Silencieux Volume Augmenter/ Diminuer Marche/Veille Suspendre/ Réactiver Barre d’état Bouton principal*Requiert une Apple TV de seconde génération. *La messagerie vocale visuelle et les MMS ne sont pas forcément disponibles dans toutes les régions. Pour en savoir plus, contactez votre fournisseur de services sans fil. Certains services et fonctionnalités ne sont pas disponibles partout. © 2010 Apple Inc. Tous droits réservés. Apple, AirPlay, Apple TV, Cover Flow, FaceTime, iPhone, iPod, iTunes, Mac et Safari sont des marques d’Apple Inc., déposées aux États-Unis et dans d’autres pays. AirPrint est une marque d’Apple Inc. iTunes Store est une marque de service d’Apple Inc., déposée aux États-Unis et dans d’autres pays. App Store et iBookstore sont des marques de service d’Apple Inc. Les autres noms de produits et de sociétés mentionnés ici peuvent être des marques de leurs détenteurs respectifs. Designed by Apple in California. Printed in China. F034-5753-A Perfectionner ses connaissances. Vous pouvez perfectionner vos connaissances sur les fonctionnalités de l’iPhone en vous rendant sur la page web www.apple.com/fr/iphone ou www.apple.com/iphone/countries. Pour consulter le Guide de l’utilisateur de l’iPhone sur votre iPhone, téléchargez-le sur l’iBookstore ou cherchez-le sur le site help.apple.com/iphone ou dans les signets de Safari. Pour obtenir des versions téléchargeables du Guide de l’utilisateur de l’iPhone et du Guide d’informations importantes sur le produit, rendez-vous sur support.apple.com/fr_FR/manuals/ iphone. Obtenir de l’assistance. Contactez votre fournisseur de services sans fil pour obtenir une assistance sur les services liés au réseau, y compris la messagerie vocale visuelle et la facturation. * Rendez-vous sur www.apple.com/fr/support/iphone pour obtenir une assistance technique sur l’iPhone et iTunes. Rechercher un lieu. Effectuer des recherches dans les environs. Pour situer où vous vous trouvez sur une carte, touchez le bouton Localisation. Un point bleu apparaît, signalant votre position géographique à cet instant. Pour connaître la direction face à vous, touchez à nouveau le bouton Localisation afin d’activer l’affichage avec orientation. Recherchez des lieux précis dans les alentours en saisissant des mots comme « Starbucks » ou « pizza » dans le champ de recherche. Touchez deux fois l’écran pour effectuer un zoom avant, et une fois avec deux doigts pour un zoom arrière. Vous pouvez également obtenir des indications sur un trajet ou faire apparaître davantage d’options d’affichage en touchant le bouton représentant une page retournée. App Store. Touchez l’icône App Store pour parcourir sans fil des centaines de milliers d’apps dans des catégories telles que jeux, entreprise, voyage ou réseaux sociaux. Parcourez-les par Sélection, Catégories ou Top 25, ou lancez une recherche par nom. Pour acheter et télécharger une application directement sur votre iPhone, touchez Acheter. Beaucoup d’applications sont gratuites. iTunes Store. Vous pouvez accéder à l’iTunes Store sans fil en touchant l’icône d’iTunes. Parcourez le Store pour y rechercher musique, films, séries télévisées, clips vidéo et plus encore. Naviguez, achetez et téléchargez depuis le Store, directement sur votre iPhone. Touchez n’importe quel élément afin d’en écouter ou d’en visionner un extrait. Clavier intelligent. L’iPhone corrige et suggère des mots automatiquement et au fur et à mesure que vous écrivez. Ainsi, si vous saisissez une lettre erronée, continuez à écrire. Pour accepter le mot suggéré, touchez la barre d’espace. Touchez le « x » pour refuser le mot suggéré et permettre à l’iPhone de mémoriser le mot que vous avez saisi. Le clavier insère automatiquement les apostrophes dans les contractions, le cas échéant. Touchez deux fois la barre d’espace pour ajouter un point. Pour activer le clavier numérique et celui des symboles, touchez le bouton « .?123 ». Couper, copier et coller. Touchez le texte que vous souhaitez modifier, ou bien touchez-le en laissant le doigt dessus afin de faire apparaître la loupe, puis faites glisser votre doigt pour déplacer le point d’insertion. Pour sélectionner un mot, touchez-le deux fois rapidement et faites glisser les points de capture pour sélectionner plus ou moins de texte. Ensuite, touchez Couper, Copier ou Coller. Pour copier du texte depuis des pages web, des courriers électroniques ou des SMS ou MMS, touchez le texte à sélectionner et maintenez le doigt dessus. Pour annuler une modification, remuez l’iPhone puis touchez le bouton d’annulation de la modification. Photos. Chargez vos photos favorites sur l’iPhone depuis votre ordinateur via iTunes, ou utilisez l’appareil photo intégré pour prendre des photos. Touchez Photos afin de voir vos photos. Passez le doigt sur l’écran vers la droite ou la gauche pour vous déplacer entre les images. Touchez deux fois l’écran rapidement ou rapprochez vos doigts dessus pour activer le zoom. Touchez une fois l’écran pour afficher les contrôles à l’écran. Touchez le bouton d’action pour envoyer une photo dans un message MMS ou un message électronique. Vous pouvez également utiliser une photo comme fond d’écran, l’affecter à un contact ou l’imprimer sans fil sur une imprimante compatible AirPrint. Vidéo HD. Pour enregistrer de la vidéo en HD, touchez Caméra puis placez le commutateur Photo/Vidéo en position Vidéo. Touchez le bouton Enregistrer afin de commencer l’enregistrement. Touchez à nouveau ce bouton pour l’arrêter. L’option « Toucher pour mettre au point » vous permet de contrôler la mise au point et l’exposition en touchant n’importe quel élément sur l’écran. L’enregistrement peut être effectué en mode paysage ou portrait. Vous pouvez même allumer la lumière de la caméra si vous filmez dans un endroit sombre. Contrôles pour les vidéos et les morceaux. Touchez l’écran pour afficher les contrôles à l’écran. Touchez-le à nouveau pour les masquer. Si vous touchez deux fois une vidéo, vous passez alors d’un affichage grand écran à un affichage plein écran. Lors de l’écoute de musique, tournez l’iPhone pour faire apparaître la pochette de l’album en mode Cover Flow et parcourir vos albums. Touchez un album pour afficher la liste de ses pistes et touchez-en une pour l’écouter. Pour revenir à la pochette de l’album, touchez l’écran à l’extérieur de la liste de pistes. Lors de l’écoute de musique avec les écouteurs de l’iPhone, appuyez sur le bouton central une fois pour mettre en pause ou en lecture, et appuyez rapidement deux fois pour passer au morceau suivant. Touchez le bouton AirPlay pour diffuser votre musique ou votre vidéo vers une Apple TV*. Voir une page web de plus près. Dans Safari, touchez deux fois un élément d’une page web (image ou texte) pour l’agrandir. Touchez à nouveau deux fois pour revenir à la taille normale. Touchez le bouton Multi-page pour feuilleter plusieurs pages web ou en ouvrir une nouvelle. Tournez l’iPhone pour visualiser la page web au format grand écran. Google, le logo Google et Google Maps sont des marques de Google Inc. © 2010. Tous droits réservés. L’App Store est disponible dans certains pays uniquement. L’iTunes Store est disponible dans certains pays uniquement. AirPort Extreme Base Station Setup Guide LL2870.book Page 1 Thursday, October 28, 2004 12:45 PMLL2870.book Page 2 Thursday, October 28, 2004 12:45 PM 3 1 Contents Chapter 1 5 Introduction to AirPort 5 About the AirPort Extreme Base Station 6 The AirPort Extreme Base Station at a Glance 7 AirPort Extreme Base Station Ports 8 About the AirPort Software Chapter 2 9 Setting Up Your AirPort Extreme Base Station 10 Mounting the AirPort Extreme Base Station on a Wall 12 Setup Overview Chapter 3 15 Using Your AirPort Extreme Base Station 15 Configuring the Base Station 16 Monitoring the AirPort Extreme Base Station’s Internet Connection Status 17 Monitoring AirPort Extreme Base Station Communication 17 Connecting to the Internet Via the AirPort Network 18 Connecting Additional Base Stations to Your AirPort Network 18 Connecting Multiple Base Stations to Power Sourcing Equipment (PSE) 18 Extending the Range of Your AirPort Network 19 Controlling the Range of Your AirPort Network 19 More Information About AirPort Chapter 4 21 Basic Network Designs 22 Setting Up a Home Office Network 23 Setting Up a Network at School 25 Connecting AirPort Base Stations Using Power Over Ethernet (PoE) Chapter 5 27 Troubleshooting Appendix 31 AirPort Extreme Base Station Specifications 33 Communications Regulation Information LL2870.book Page 3 Thursday, October 28, 2004 12:45 PM4 Contents LL2870.book Page 4 Thursday, October 28, 2004 12:45 PM1 5 1 Introduction to AirPort AirPort is a simple and fast way to access the Internet from anywhere in your home, classroom, or office without cables, additional phone lines, or complicated networking software. AirPort is a wireless local area network (WLAN) technology that provides highperformance wireless communication between multiple computers and the Internet. When you connect to the Internet using AirPort, you can share a single Internet connection with many computers at the same time and share files among them. To use AirPort to access the Internet, you may need an account with an Internet service provider (fees may apply) and a way to access the Internet—either through a DSL or cable modem, or an Ethernet network. If your base station has an internal modem, and you have a PPP dial-up connection with an ISP, you can connect to the Internet using the base station’s internal modem. Note: This manual includes information for setting up the AirPort Extreme Base Station using Mac OS X and Windows XP and Windows 2000. The screenshots and general instructions are based on Mac OS X. For more detailed Windows XP and Windows 2000 instructions, see AirPort Help in the AirPort Admin Utility on computers using Windows. About the AirPort Extreme Base Station The AirPort Extreme Base Station establishes a wired connection to the Internet or a network and wireless connections to wireless client computers. Once the base station is connected to the network, all wireless client computers can connect to the Internet by joining the AirPort network. Computers connected to the AirPort network by Ethernet can also share the base station’s Internet connection. The base station manages communications between the Internet and the wireless client computers. LL2870.book Page 5 Thursday, October 28, 2004 12:45 PM6 Chapter 1 Introduction to AirPort The AirPort Extreme Base Station has the following ports: • 10/100Base-T Ethernet WAN ( ) port for connecting a DSL or cable modem, or for connecting to an existing Ethernet network with Internet access • 10/100Base-T Ethernet LAN (G) port for high-speed connection to local printers and Ethernet computers that don’t have Internet access • USB port ( ) for connecting a printer to the base station Some models of the base station also have a built-in 56K modem port (W) for dial-up Internet access with a standard telephone line. Some models of the base station can also receive power over Ethernet (PoE). When the base station Ethernet WAN port is connected to IEEE 802.3af-compliant Power Sourcing Equipment (PSE), such as a line-powered Ethernet switch or hub, with a CAT 5 Ethernet cable, it receives power over the Ethernet cable. The AirPort Extreme Base Station at a Glance Status lights Internal modem port Ethernet (LAN) port Power adapter port Security slot Ethernet (WAN) port USB printer port Reset button External antenna port LL2870.book Page 6 Thursday, October 28, 2004 12:45 PMChapter 1 Introduction to AirPort 7 AirPort Extreme Base Station Ports Your AirPort Extreme Base Station may have six ports, depending on which model you purchased. Note: If this AirPort Extreme Base Station did not come with a power adapter and you don’t plan to use PoE, you can purchase a base station power adapter from your Appleauthorized dealer, Apple retail stores, or the Apple Store at www.apple.com/store. If the base station supports PoE, it and its mounting bracket conform to UL Standard 2043, “Fire Test for Heat and Visible Smoke Release for Discrete Products and Their Accessories Installed in Air-Handling Spaces,” for placement in the air-handling space above suspended ceilings. Using PoE allows you to install a base station in places away from a standard electrical outlet. For more information about using PoE, see the document “Designing AirPort Extreme Networks,” or “AirPort Networks for Windows,” that came on the AirPort CD. The documents are also available at www.apple.com/airportextreme. To determine if your base station supports PoE, check the label on the bottom of the base station. Note: To use the base station in an air-handling space above suspended ceilings, you must connect the Ethernet WAN port to an 802.3af-compliant PSE with a plenum-rated Ethernet cable. You cannot use the AC power adapter to power a base station installed in an air-handling space. If you connect an external antenna to a base station mounted in an air-handling space, make sure it is plenum-rated. See the documentation that came with the antenna. 10/100Base-T Ethernet WAN port Connect a DSL or cable modem, or connect to an existing Ethernet network with Internet access. G 10/100Base-T Ethernet LAN port Connect local Ethernet computers (computers without Internet access) and printers, or other Ethernet devices, such as a hub or a switch. W Internal modem port (on some models) Connect one end of a phone cord to the internal modem port and the other end to a standard telephone jack. Universal Serial Bus (USB) printer port Connect a USB printer so that computers connected to the AirPort network can share the printer. External antenna port Connect an Apple-certified external antenna to extend the range of the wireless network. ¯ Power adapter port Connect one end of the AirPort Extreme Base Station power adapter to the port and the other end to an electrical outlet. Security slot You can purchase a security cable and lock to secure your AirPort Extreme Base Station. LL2870.book Page 7 Thursday, October 28, 2004 12:45 PM8 Chapter 1 Introduction to AirPort About the AirPort Software To extend the range of your network, you can use AirPort Admin Utility to set up multiple base stations in your network connected to one another wirelessly, known as a Wireless Distribution System (WDS), or over Ethernet. You can also extend the range of your wireless network by connecting an Apple-certified external antenna to the antenna port. If you connect a USB printer to the base station, computers on the AirPort network can print to it by selecting the printer via Rendezvous in Printer Setup Utility, located in Applications/Utilities on a Macintosh. You must use Mac OS X v10.2.3 or later, or Windows XP or Windows 2000, to print to a USB printer via an AirPort Extreme Base Station. For information about setting up a computer using Windows XP or Windows 2000, see the document “AirPort Networks for Windows,” that came on the AirPort CD. Note: If the base station is set up to receive power over the Ethernet WAN port, do not connect a printer to the USB port. You cannot print to a USB printer if the base station is powered over Ethernet. AirPort Setup Assistant Use the AirPort Setup Assistant to configure the AirPort Extreme Base Station and to set up your computer to use AirPort. The Assistant is located in Applications/Utilities on a computer using Mac OS X. AirPort Admin Utility AirPort Admin Utility is an advanced tool for setting up and managing the AirPort Extreme Base Station. Use AirPort Admin Utility to adjust network, routing, and security settings and other advanced options. AirPort Admin Utility is located in Applications/ Utilities on a computer using Mac OS X, and in Start > All Programs > AirPort on a computer using Windows XP or Windows 2000. AirPort status menu in the menu bar Use the AirPort status menu to switch quickly between AirPort networks, monitor the signal quality of the current network, create a Computer-to-Computer network, and turn AirPort on and off. The AirPort status menu in the menu bar is part of AirPort for Max OS X. If your base station supports Power over Ethernet, the following Mac OS X applications are included on the AirPort Management Tools CD. AirPort Management Utility AirPort Management Utility allows network administrators to set up and manage multiple base stations from a single location. AirPort Client Monitor The AirPort Client monitor application monitors the signal strength and transmit rate of wireless client computers. LL2870.book Page 8 Thursday, October 28, 2004 12:45 PM2 9 2 Setting Up Your AirPort Extreme Base Station Use the information in this chapter to set up your AirPort Extreme Base Station. Before you set up the AirPort Extreme Base Station for Internet access, make sure that: • You have a computer with an AirPort Card or an AirPort Extreme Card, or a compatible Wi-Fi card installed in a computer using Windows XP or Windows 2000. • Your computer has the latest version of the AirPort software installed. For the latest information on AirPort software, check Software Update in System Preferences or the following Apple websites: • Apple AirPort website at www.apple.com/airportextreme • Apple Support website at www.apple.com/support • You have an account with an Internet service provider (fees may apply) or you have Internet access through a network. For more information on using AirPort with your Internet account, contact your Internet service provider (ISP) or go to the Apple Service & Support website at support.apple.com. • You have a suitable location for your AirPort Extreme Base Station. You can place your AirPort Extreme Base Station on a desk, bookcase, or other flat surface, or you can mount it on a wall. Place your base station in the center of your home or office, away from any source of interference or signal blockage, such as a microwave oven or large metal appliances, and close to a power outlet. If the base station supports PoE, it is suitable for use in environmental air-handling spaces (in accordance with section 300.22(C) of the National Electrical Code and 12-010 of the Canadian Electrical Code), and capable of receiving power over Ethernet. You can install it in a ceiling air-handling space, away from a power outlet. If you install the base station in an air-handling space, you need to connect the Ethernet WAN port to 802.3af-compliant Power Sourcing Equipment (PSE) with a plenum-rated Ethernet cable. If you connect the base station power adapter to an outlet, the Ethernet WAN port no longer receives power from a PSE. LL2870.book Page 9 Thursday, October 28, 2004 12:45 PM10 Chapter 2 Setting Up Your AirPort Extreme Base Station If you use an Ethernet LAN for Internet access, such as in a school or office, connect the Ethernet cable to the 10/100Base-T Ethernet LAN (G) port on the AirPort Extreme Base Station. Note: The “Distribute IP address” checkbox in the Network pane of AirPort Admin Utility is deselected for AirPort Extreme Base Stations that support Power over Ethernet. By default the base stations are set to be used as a bridge, rather than to distribute IP addresses to AirPort clients. For more information on AirPort Admin Utility and using the 10/100Base-T Ethernet LAN (G) port, see the document “Designing AirPort Extreme Networks,” or “AirPort Networks for Windows,” located on the AirPort CD or at www.apple.com/airportextreme. You can use the AirPort Extreme Base Station to provide Internet access to non-AirPort computers that are not otherwise connected to the Internet by connecting them to the 10/100Base-T Ethernet LAN (G) port on the AirPort Extreme Base Station. The base station must be connected to the Internet by the 10/100Base-T Ethernet WAN ( ) port. Mounting the AirPort Extreme Base Station on a Wall You can use the mounting bracket provided with your AirPort Extreme Base Station to mount the base station on a wall. Follow these steps: 1 Select a location close to power and a network connection. If the base station is UL rated and certified for use in suspended ceilings and airhandling spaces, the base station can be mounted in a ceiling space, away from a power outlet, and powered over Ethernet. If you mount the base station in an airhandling space, plug the base station into 802.3af-compliant Power Sourcing Equipment with a plenum-rated Ethernet cable. 2 Screw the mounting bracket into a wall stud using the two screws that came with the base station. Mounting bracket LL2870.book Page 10 Thursday, October 28, 2004 12:45 PMChapter 2 Setting Up Your AirPort Extreme Base Station 11 3 Locate the two mounting bracket holes on the bottom of the base station. 4 Feed the cables through the mounting bracket and then connect them to the base station. The base station is designed to mount with the ports on the top (Apple logo right side up), with the cables passing behind it through the mounting bracket as shown. Note: The mounting bracket has enough space for six cables (power, two Ethernet cables, USB printer cable, a telephone cable, and external antenna cable). In most cases, only two or three cables are used. Mounting bracket holes LL2870.book Page 11 Thursday, October 28, 2004 12:45 PM5 Carefully insert the bottom two prongs on the mounting bracket into the mounting bracket holes on the bottom of the base station. Clip the top prongs on the mounting bracket around the bottom lip of the base station. Setup Overview Once you’re ready, you can set up the AirPort Extreme Base Station in a few steps: 1 Plug the AirPort Extreme Base Station in to a power outlet and connect it to your Internet networking interface. 2 Use the AirPort Setup Assistant on a Macintosh, or use AirPort Admin Utility on a Windows XP or Windows 2000 computer. Step 1: Connect the AirPort Extreme Base Station 1 Connect the power adapter to the AirPort Extreme Base Station power adapter port and an electrical outlet. Important: Use only the power adapter that came with your AirPort Extreme Base Station. Adapters for other electronic devices may look similar, but they may damage the base station. The AirPort Extreme Base Station turns on when the power adapter is plugged into an electrical outlet. There is no power switch. When you plug in the base station, the status lights glow while the base station starts up. Only the middle light glows when startup is complete. The startup process takes about 30 seconds. See “Monitoring AirPort Extreme Base Station Communication” on page 17 for a complete explanation of the lights on the AirPort Extreme Base Station. 2 Connect the AirPort Extreme Base Station to your DSL or cable modem, Ethernet network, or, if your base station has an internal modem, a standard phone line. • If you have an Internet account that uses a device such as a DSL or cable modem, connect the device to the 10/100Base-T Ethernet WAN ( ) port on the AirPort Extreme Base Station. • If you use an Ethernet LAN for Internet access, such as in a school or office, connect the Ethernet cable to the 10/100Base-T Ethernet LAN (G) port on the AirPort Extreme Base Station. • If you use a standard modem and analog telephone line (the type of telephone line found in most residences) to access the Internet, connect one end of the phone cord to the internal modem (W) port and the other end to your telephone jack. Important: Do not connect the base station to a digital telephone line, such as a PBX telephone system. LL2870.book Page 12 Thursday, October 28, 2004 12:45 PMChapter 2 Setting Up Your AirPort Extreme Base Station 13 If your base station has a built-in modem and you connect to the Internet using it, the base station can provide Internet access to computers connected to both Ethernet ports (WAN and LAN G). Step 2: Use the AirPort Setup Assistant on a Macintosh computer The AirPort Setup Assistant: • Sets up your AirPort network • Configures your computer to access the AirPort network created by the AirPort Extreme Base Station Note: You can’t use the AirPort Setup Assistant to set up some advanced features. Use AirPort Admin Utility, located in Applications/Utilities. To use the AirPort Setup Assistant to configure the AirPort Extreme Base Station: 1 Make sure you have plugged in the base station and the middle light is on. 2 Open the AirPort Setup Assistant (in Applications/Utilities on a Mac, and follow the onscreen instructions. Use AirPort Admin Utility on a Windows XP or Windows 2000 computer See the document “AirPort Networks for Windows” that came on the AirPort CD for detailed instructions for setting up your AirPort Extreme Base Station using AirPort Admin Utility. LL2870.book Page 13 Thursday, October 28, 2004 12:45 PMLL2870.book Page 14 Thursday, October 28, 2004 12:45 PM3 15 3 Using Your AirPort Extreme Base Station The information in this chapter will help you understand how to use your base station and how to get the most from your AirPort network. Use the information provided in this chapter to: • Configure your base station’s Internet connection • Use AirPort Admin Utility to modify advanced base station settings • Monitor your AirPort Extreme Base Station status • Connect to and disconnect from the AirPort network • Connect additional base stations to your AirPort network • Extend the range of your AirPort network Configuring the Base Station The AirPort Setup Assistant provides complete configuration options for most AirPort networks. For advanced settings, you can use AirPort Admin Utility (in Applications/Utilities) to configure your AirPort Extreme Base Station. You can use AirPort Admin Utility to do the following: • Configure your AirPort network, including changing the network name and password and specifying whether users need a password to join your network. • Change the AirPort Extreme Base Station name and password. • Set advanced security settings, like Wi-Fi Protected Access (WPA). • Enter the TCP/IP settings for your AirPort Extreme Base Station. • Set up the way Internet access is provided to computers on the AirPort network. • Set up multiple base stations on a single AirPort network. Note: If your base station does not support PoE, by default it is set to use the Internet Dynamic Host Configuration Protocol (DHCP) and Network Address Translation (NAT) to share a single IP address. If your base station supports PoE, by default it is set up as a bridge, and the “Distribute IP address” checkbox is deselected in the Network pane of AirPort Admin Utility. LL2870.book Page 15 Thursday, October 28, 2004 12:45 PM16 Chapter 3 Using Your AirPort Extreme Base Station Important: If you use AirPort Admin Utility instead of the AirPort Setup Assistant to configure your base station for the first time, you may be asked for a password. The initial password for the AirPort Extreme Base Station is public. See the document “Designing AirPort Extreme Networks,” or “AirPort Networks for Windows,” located on the AirPort CD and at www.apple.com/airportextreme, for indepth information on designing and setting up your AirPort network using the AirPort Setup Assistant and AirPort Admin Utility. If you are setting up larger AirPort Extreme networks with base stations that support PoE, you can also use AirPort Management Utility and AirPort Client Monitor (on the Management Tools CD) to set up and manage multiple base stations. See the document “Managing AirPort Extreme Networks,” located on the Management Tools CD, and at www.apple.com/airportextreme, for information and instructions for setting up, managing, and monitoring larger AirPort Extreme networks. Monitoring the AirPort Extreme Base Station’s Internet Connection Status Use the Internet Connect application, located in the Applications folder on a Macintosh, to monitor the wireless signal level and status of your AirPort Extreme Base Station’s Internet connection, as shown below. Use the Wireless Connection Status menu on a Windows XP or Windows 2000 computer to monitor the wireless signal level. LL2870.book Page 16 Thursday, October 28, 2004 12:45 PMChapter 3 Using Your AirPort Extreme Base Station 17 Monitoring AirPort Extreme Base Station Communication The following table explains the AirPort Extreme Base Station indicator lights. For more information about the base station’s indicator lights, see “Designing AirPort Extreme Networks,” or AirPort Networks for Windows,” located on the AirPort CD, or at www.apple.com/airportextreme. Connecting to the Internet Via the AirPort Network If your computer is connected to an AirPort network that has continuous Internet access via Ethernet, DSL, or a cable modem, you may already be connected to the Internet and can open and use any application that requires an Internet connection, such as a web browser or email application. If you are not connected, open Internet Connect, located in the Applications folder, click AirPort in the toolbar, and click Connect. Light number Indicator Status 1 Flashing The AirPort Extreme Base Station is communicating via AirPort. 2 Steady glow The AirPort Extreme Base Station is receiving power and is in normal operating mode. 3 Flashing The AirPort Extreme Base Station is communicating via the LAN port. 1 2 3 LL2870.book Page 17 Thursday, October 28, 2004 12:45 PM18 Chapter 3 Using Your AirPort Extreme Base Station Connecting Additional Base Stations to Your AirPort Network You can connect additional AirPort Extreme Base Stations to extend the range of your wireless network. You can connect the base stations wirelessly or using Ethernet. A network with base stations connected using Ethernet is known as a roaming network. Connecting base stations wirelessly creates what is known as a Wireless Distribution System (WDS). See the document “Designing AirPort Extreme Networks,” or “AirPort Networks for Windows” for more information about setting up a roaming network or extending your network with WDS. Connecting Multiple Base Stations to Power Sourcing Equipment (PSE) If your base stations support PoE, you can connect multiple base stations to an 802.3afcompliant Ethernet device (known as a PSE), and send power and a network or Internet connection over category 5 Ethernet cables. Receiving power over the base station’s Ethernet connection eliminates extra cables and the need to locate the base station near a power outlet. Base stations that support PoE meet flammability classification standards and are UL listed for use above suspended ceilings and in air-handling spaces. The US National Electric Code (NEC) and the Canadian Electrical Code (CEC) require that you use plenum-rated Ethernet cables in air-handling spaces. Extending the Range of Your AirPort Network In addition to adding base stations to your network, you can attach an Apple-certified external antenna to the base station to extend your network’s range. External antennas are available from your Apple-authorized dealer, Apple retail stores, or the Apple Store at store.apple.com. External antennas may not be permitted in some regions outside the US. If your base station supports PoE and is mounted in an air-handling space and receives power over the Ethernet WAN port, do not connect an external antenna unless it is plenum-rated and conforms to UL Standard 2043. Note: Before connecting or disconnecting an external antenna, you must unplug the base station’s power adapter, connect or disconnect the antenna, and then plug the base station back in to its power source. LL2870.book Page 18 Thursday, October 28, 2004 12:45 PMChapter 3 Using Your AirPort Extreme Base Station 19 Controlling the Range of Your AirPort Network You can also shorten the range of your AirPort network by adjusting the power transmitted to the radio in the base station. This might be useful if you want to control access to the network by restricting the range to a single room, for example. To shorten the range of your AirPort network: 1 Open AirPort Admin Utility, in Applications/Utilities on a Macintosh and in Start > All Programs > AirPort on a Windows XP or Windows 2000 computer. 2 Select your base station and click Configure. 3 On a Macintosh, click Wireless Options. On a Windows XP or Windows 2000 computer, click AirPort. 4 Choose a percentage from the Transmitter Power slider. More Information About AirPort You can find more information about AirPort in the following locations: • AirPort Help Look in AirPort Help for information on setting up an AirPort network, using an AirPort Base Station, editing base station settings, avoiding sources of interference, locating additional information on the Internet, and more. Choose Help > Mac Help, and then choose Library > AirPort Help. • “Designing AirPort Extreme Networks” For in-depth information on configuring AirPort networks, see the “Designing AirPort Extreme Networks” document, located at www.apple.com/airportextreme. • “Managing AirPort Extreme Networks” For in-depth information on setting up and managing multiple base stations in AirPort networks, see the “Managing AirPort Extreme Networks” document, located at www.apple.com/support/airportextreme. • “AirPort Networks for Windows” For in-depth information on configuring AirPort networks from a Microsoft Windows computer, see the “AirPort Networks for Windows” document, located at www.apple.com/airportextreme. • AirPort website www.apple.com/airportextreme • Apple Support website www.apple.com/support LL2870.book Page 19 Thursday, October 28, 2004 12:45 PMLL2870.book Page 20 Thursday, October 28, 2004 12:45 PM4 21 4 Basic Network Designs You can set up your AirPort Extreme Base Station just about anywhere and use it for Internet access and wireless networking. You need only a connection to the Internet and a computer with wireless capabilities. You can even add non-wireless computers to the network by connecting them to the base station through the built-in Ethernet LAN (G) port. Connect a USB printer to the base station, and all the computers on the network using Mac OS X v10.2.3 or later, both wired and wireless, can share the printer. If you want to extend the range of your AirPort network, connect an Apple-certified external antenna to the base station antenna port. Apple-certified external antennas for the AirPort Extreme Base Station are available from your Apple-authorized dealer, Apple retail stores, or the Apple Store at store.apple.com. Note: External antennas may not be permitted in some regions. Do not connect an external antenna to a base station that supports PoE and is mounted in the air space above a ceiling. This chapter explains how to set up your base station: • In your home or small office with an Ethernet or dial-up connection to the Internet • In school, where you might have both a broadband and an Ethernet connection • In a business or school using Power over Ethernet LL2870.book Page 21 Thursday, October 28, 2004 12:45 PM22 Chapter 4 Basic Network Designs Setting Up a Home Office Network If you are setting up an AirPort network in your home or small office and you have a broadband DSL or cable modem connection to the Internet, and an existing Ethernet network, you may need the following items: • An AirPort Extreme Base Station or multiple base stations • A DSL or cable modem with Internet access • AirPort- or other wireless-equipped computers • An optional Ethernet network The following illustration is an example of an AirPort network in an office. The AirPort Extreme Base station is connected by the Ethernet WAN ( ) port to the DSL or cable modem (if your base station came with a built-in modem, you can use it to connect). The base station shares its Internet connection with the AirPort-equipped computers wirelessly and with computers connected to the Ethernet LAN (G) port. For more information on AirPort Extreme network designs, see “Designing AirPort Extreme Networks,” located at www.apple.com/airport. For information on managing larger AirPort Extreme networks, see “Managing AirPort Extreme Networks,” located at www.apple.com/support/airport. To the Internet To Ethernet (LAN) To USB printer Power adapter USB LL2870.book Page 22 Thursday, October 28, 2004 12:45 PMChapter 4 Basic Network Designs 23 Setting Up a Network at School If you are setting up a network at school, and have a broadband DSL or cable modem connection to the Internet, and an existing Ethernet network, you may need the following items: • An AirPort Extreme Base Station or multiple base stations • A DSL or cable modem with Internet access • AirPort- or other wireless-equipped computers • An optional Apple-certified external antenna The following illustration is an example of an AirPort network in a school with multiple rooms or buildings. The AirPort Extreme Base Stations are set up as a Wireless Distribution System (WDS), with the main base station connected by the Ethernet WAN ( ) port to the DSL or cable modem. The main base station shares its Internet connection with the wireless computers in the room, or with computers connected to the main base station’s Ethernet LAN (G) port. The main base station also shares the Internet connection with the relay base station in the other room or building. The relay base station transfers the Internet connection to a remote base station set up in a third building. The relay and remote base stations can be set up to share the Internet connection with wireless computers in the room, or computers connected to the base station’s Ethernet LAN (G) port. LL2870.book Page 23 Thursday, October 28, 2004 12:45 PM24 Chapter 4 Basic Network Designs USB Main To the Internet To Ethernet (LAN) Power adapter To USB printer Remote Relay LL2870.book Page 24 Thursday, October 28, 2004 12:45 PMChapter 4 Basic Network Designs 25 Connecting AirPort Base Stations Using Power Over Ethernet (PoE) You can connect multiple base stations that support PoE to 802.3af-compliant Power Sourcing Equipment (PSE), and send power and a network or Internet connection over Ethernet cables. Receiving power over the Ethernet connection eliminates extra cables and the need to locate the base station near a power outlet. The following illustration is an example of an AirPort network in a business or school with multiple rooms or buildings. Plenum-rated Ethernet cables connect to the Ethernet WAN ( ) ports on the base stations and to an 802.3af-compliant PSE. The base stations are mounted in the ceiling air-handling space, and are secure and out of sight. When the base stations receive power and a network connection over the WAN port, the USB port is disabled. You can connect the Ethernet LAN port to a computer or other Ethernet device, but power does not travel to the Ethernet LAN port. Important: Do not connect an external antenna to a base station mounted in an airhandling space above a suspended ceiling unless it is plenum-rated and conforms to UL Standard 2043. LL2870.book Page 25 Thursday, October 28, 2004 12:45 PM26 Chapter 4 Basic Network Designs To 802.3af-compliant PSE Base stations mounted in air-handling space 802.3af-compliant Power Sourcing Equipment (PSE) connected to a network Plenum-rated Ethernet cables AC power outlet Plenum-rated Ethernet cables Base stations mounted in air-handling space LL2870.book Page 26 Thursday, October 28, 2004 12:45 PM5 27 5 Troubleshooting Use the information in this chapter if you are having trouble setting up your AirPort Extreme Base Station. If the AirPort Setup Assistant can’t detect the proper AirPort hardware Make sure that the computer you are using has an AirPort Card or an AirPort Extreme Card installed. If you recently installed the card, shut down your computer and make sure the card is properly installed. Make sure that the AirPort antenna cable is securely connected to the card (you should hear a click when the antenna is connected securely). Make sure that the other end of the card is firmly inserted into the connector in the AirPort Card slot. If you forget your AirPort network or base station password You can clear the AirPort network or base station password by resetting the base station. Follow these steps: 1 On a Mac, open Network preferences. Choose AirPort from the Show pop-up menu and choose Using DHCP from the Configure pop-up menu. On a computer using Windows XP or Windows 2000, open Control Panel from the Start menu, right-click Wireless Network Connection and choose Properties. Click Internet Protocol (TCP/IP) and click Properties. Make sure “Obtain an IP address automatically” is selected. 2 Press and hold the reset button for one full second. Reset button LL2870.book Page 27 Thursday, October 28, 2004 12:45 PM28 Chapter 5 Troubleshooting The middle light flashes, indicating that the base station is in reset mode. The base station remains in reset mode for five minutes. If you do not make your changes within five minutes of pressing the reset button, you must reset it again. 3 Use the AirPort status menu in the menu bar to select the network created by the base station (the network name does not change). 4 Open AirPort Admin Utility (in Applications/Utilities on a Mac, and in Start > All Programs > AirPort on a Windows computer). 5 Select your base station and click Configure. 6 In the dialog that appears, make the following changes: • Reset the AirPort Extreme Base Station password. • Turn encryption on to activate password protection for your AirPort network. If you turn on encryption, enter a new password for your AirPort network. 7 Click OK. The base station restarts to load the new settings. Note: While the base station is in reset mode, access control and RADIUS settings are temporarily interrupted. All of the base station settings will be available after the base station has restarted. If your base station isn’t responding Try unplugging the base station and plugging it back in to a power outlet. If power is supplied over Ethernet, make sure the cables are properly connected and the PSE is plugged in and working correctly. If your base station stops responding completely, you may need to reset it to the factory default settings. This erases all of the settings you’ve made and resets them to the settings that came with the base station. To return the base station to the factory settings: m Press and hold the reset button for five full seconds. The base station restarts with the following settings: • The base station receives its IP address using DHCP. • The network name reverts to Apple Network XXXXXX (where X is a letter or number). • The base station password returns to public. Important: Resetting the base station to factory defaults erases all the settings you have entered for the base station, including access control and RADIUS settings. LL2870.book Page 28 Thursday, October 28, 2004 12:45 PMChapter 5 Troubleshooting 29 If you move your AirPort Extreme Base Station to a location on your network with a different subnet and lose communication with the base station Your AirPort Extreme Base Station may have an invalid IP address. 1 Make sure that your computer is set to access the network from the new location (where you moved the AirPort Extreme Base Station) and that it is in range of the base station. 2 Make sure that the computer is set to use AirPort. 3 Use the AirPort Setup Assistant to reconfigure the base station. Important: You cannot use the AirPort Setup Assistant if you have used AirPort Admin Utility to turn off Internet sharing for your base station. If Internet sharing is turned off, you need to reset your base station and enter a new IP address. See “If you forget your AirPort network or base station password” on page 27. If your printer isn’t responding If you connected a printer to the USB port on the base station and the computers on the AirPort network can’t print, try doing the following: 1 Make sure the printer is plugged in and turned on. 2 Make sure the cables are securely connected to the printer and to the base station’s USB port. 3 Make sure the printer is selected in the Printer List on client computers. To do this: a Open Printer Setup Utility, located in Applications/Utilities. b If the printer is not in the list, click Add. c Choose Rendezvous from the pop-up menu. d Select the printer and click Add. Note: If the base station is set up to receive power over Ethernet, the USB port is disabled. You cannot print to a USB printer connected to the USB port if the base station is powered over Ethernet. LL2870.book Page 29 Thursday, October 28, 2004 12:45 PMLL2870.book Page 30 Thursday, October 28, 2004 12:45 PM 31 Appendix AirPort Extreme Base Station Specifications AirPort Specifications • Wireless Data Rate: Up to 54 megabits per second (Mbps) • Range: Up to 150 feet (45 meters) in typical use (varies with building) • Frequency Band: 2.4 gigahertz (GHz) • Radio Output Power: 15 dBm (nominal) • Standards: Compliant with 802.11 HR Direct Sequence Spread Spectrum (DSSS) 11 Mbps standard, 802.11 DSSS 1 and 2 Mbps standard, and 802.11g specification Interfaces • RJ-45 Ethernet WAN connector for built-in 10/100Base-T ( ). The WAN port may accept power as a Class 0 IEEE 802.3af-compliant Powered Device (PD). • RJ-45 Ethernet LAN connector for built-in 10/100Base-T (G) • Universal Serial Bus (USB) printing ( ) • AirPort Environmental Specifications • Operating Temperature: 32° F to 95° F (0° C to 35° C) • Storage Temperature: –13° F to 140° F (–25° C to 60° C) • Relative Humidity (Operational): 20% to 80% relative humidity • Relative Humidity (Storage): 10% to 90% relative humidity, noncondensing • Operating Altitude: 0 to 10,000 feet (0 to 3048 m) • Maximum Storage Altitude: 15,000 feet (4572 m) Size and Weight • Diameter: 6.9 inches (175 mm) • Height: 3.2 inches (80 mm) • Weight: 1.25 pounds (565 grams) not including the mounting bracket LL2870.book Page 31 Thursday, October 28, 2004 12:45 PM32 Appendix AirPort Extreme Base Station Specifications Base Station LED Sequences The following table explains the base station’s light sequences and what they indicate. Left Center Right Status/description Off Off Off The base station is unplugged or has failed. If the base station is plugged in and all lights are off, contact your Apple-authorized service provider. On On On The base station is in self-check mode. Rapid sequenced flashing, right-to-left The base station is starting up. Slowly flashing Slowly flashing Slowly flashing The base station has failed the power-on self-test. Contact your Apple-authorized service provider. Off Flashing slowly Off The base station is being reset. The network and base station passwords are reset to public. Off Flashing three times Off The base station is being reset, and all settings are returned to their factory defaults. Off/Flashing On Off/Flashing Left and right flashing indicates normal network activity. The left LED flashing indicates AirPort wireless activity and the right LED flashing indicates Ethernet or network activity. LL2870.book Page 32 Thursday, October 28, 2004 12:45 PM 33 Communications Regulation Information FCC Declaration of Conformity This device complies with part 15 of the FCC rules. Operation is subject to the following two conditions: (1) This device may not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation. See instructions if interference to radio or television reception is suspected. Radio and Television Interference The equipment described in this manual generates, uses, and can radiate radio-frequency energy. If it is not installed and used properly—that is, in strict accordance with Apple’s instructions—it may cause interference with radio and television reception. This equipment has been tested and found to comply with the limits for a Class B digital device in accordance with the specifications in Part 15 of FCC rules. These specifications are designed to provide reasonable protection against such interference in a residential installation. However, there is no guarantee that interference will not occur in a particular installation. You can determine whether your computer system is causing interference by turning it off. If the interference stops, it was probably caused by the computer or one of the peripheral devices. If your computer system does cause interference to radio or television reception, try to correct the interference by using one or more of the following measures: • Turn the television or radio antenna until the interference stops. • Move the computer to one side or the other of the television or radio. • Move the computer farther away from the television or radio. • Plug the computer into an outlet that is on a different circuit from the television or radio. (That is, make certain the computer and the television or radio are on circuits controlled by different circuit breakers or fuses.) If necessary, consult an Apple-authorized service provider or Apple. See the service and support information that came with your Apple product. Or, consult an experienced radio/television technician for additional suggestions. Important: Changes or modifications to this product not authorized by Apple Computer, Inc., could void the FCC Certification and negate your authority to operate the product. This product was tested for FCC compliance under conditions that included the use of Apple peripheral devices and Apple shielded cables and connectors between system components. It is important that you use Apple peripheral devices and shielded cables and connectors between system components to reduce the possibility of causing interference to radios, television sets, and other electronic devices. You can obtain Apple peripheral devices and the proper shielded cables and connectors through an Apple-authorized dealer. For non-Apple peripheral devices, contact the manufacturer or dealer for assistance. Responsible party (contact for FCC matters only): Apple Computer, Inc., Product Compliance, 1 Infinite Loop M/S 26-A, Cupertino, CA 95014-2084, 408-974-2000. Use in Air-Handling Spaces This device has been designed and tested for use in environmental air handling spaces, in accordance with Section 300.22(C) of the National Electrical Code, and Sections 2-128, 12-010(3), and 12-100 of the Canadian Electrical Code, Part 1, C22.1. Peut étre utilisé dans des gaines transportant de l’air traité, coonformément à la section 300.22(C) du National Electrical Code et aux articles 2-128, 12- 010(3) et 12-100 du Code Canadien de l’électricité, Premiére partie C22.1. Industry Canada Statement This Class B device meets all requirements of the Canadian interference-causing equipment regulations. Cet appareil numérique de la Class B respecte toutes les exigences du Règlement sur le matériel brouilleur du Canada. LL2870.book Page 33 Thursday, October 28, 2004 12:45 PM34 VCCI Class B Statement Europe — EU Declaration of Conformity Complies with European Directives 72/23/EEC, 89/336/EEC, 1999/5/EC See http://www.apple.com/euro/compliance/ © 2004 Apple Computer, Inc. All rights reserved. Apple, the Apple logo, AirPort, AppleTalk, Mac, and Mac OS are trademarks of Apple Computer, Inc., registered in the U.S. and other countries. Rendezvous is a trademark of Apple Computer, Inc. AppleCare and AppleStore are service marks of Apple Computer, Inc., registered in the U.S. and other countries. Wi-Fi is a registered certification mark, and Wi-Fi Protected Access is a certification mark of the Wi-Fi Alliance. LL2870.book Page 34 Thursday, October 28, 2004 12:45 PMLL2870.book Page 35 Thursday, October 28, 2004 12:45 PMwww.apple.com/airport www.apple.com/support/airport 034-2870-A Printed in XXXX LL2870.book Page 36 Thursday, October 28, 2004 12:45 PM LiveType 2 User ManualK Apple Inc. Copyright © 2005 Apple Inc. All rights reserved. Your rights to the software are governed by the accompanying software license agreement. The owner or authorized user of a valid copy of Final Cut Studio software may reproduce this publication for the purpose of learning to use such software. No part of this publication may be reproduced or transmitted for commercial purposes, such as selling copies of this publication or for providing paid for support services. The Apple logo is a trademark of Apple Inc., registered in the U.S. and other countries. Use of the “keyboard” Apple logo (Shift-Option-K) for commercial purposes without the prior written consent of Apple may constitute trademark infringement and unfair competition in violation of federal and state laws. Every effort has been made to ensure that the information in this manual is accurate. Apple is not responsible for printing or clerical errors. Note: Because Apple frequently releases new versions and updates to its system software, applications, and Internet sites, images shown in this book may be slightly different from what you see on your screen. Apple Inc. 1 Infinite Loop Cupertino, CA 95014–2084 408-996-1010 www.apple.com Apple, the Apple logo, AppleWorks, Final Cut, Final Cut Pro, Final Cut Studio, FireWire, Keynote, LiveType, Mac, Macintosh, and QuickTime are trademarks of Apple Inc., registered in the U.S. and other countries. Finder is a trademark of Apple Inc. AppleCare is a service mark of Apple Inc., registered in the U.S. and other countries. Helvetica is a registered trademark of Heidelberger Druckmaschinen AG, available from Linotype Library GmbH. Other company and product names mentioned herein are trademarks of their respective companies. Mention of third-party products is for informational purposes only and constitutes neither an endorsement nor a recommendation. Apple assumes no responsibility with regard to the performance or use of these products. 3 1 Contents Preface 7 An Introduction to LiveType 7 How Does Titling Work? 8 A Realm of Creative Possibilities 9 Workflow for Creating Titles 10 About This Manual 10 LiveType Onscreen User Manual 11 Apple Websites Chapter 1 13 The LiveType Interface 14 Canvas 20 Inspector 25 Media Browser 26 Timeline 28 LiveType Media Files Chapter 2 31 Setting Up a Project 31 Templates 33 Starting a New Project and Setting Defaults 34 Setting Project Properties Chapter 3 41 Adding a Background 41 Setting a Background Color 42 Adding a Background Texture 43 Importing a Background Movie or Still Image 45 Considerations for Rendering the Background Chapter 4 47 Working With Tracks 48 Positioning Tracks in the Canvas 49 Creating Angles and Curves 51 Linking Endpoints 52 Adding, Copying, and Deleting Tracks 53 Working With Tracks in the Timeline4 Contents Chapter 5 57 Working With Text 57 Inserting Text 60 Adjusting the Timing of LiveFonts 62 Formatting Text 68 Enhancing Text With Styles 72 Creating a Matte 77 Modifying Individual Characters 78 Disabling Fonts in Mac OS X Chapter 6 79 Working With Objects, Textures, and Imported Elements 80 Working With LiveType Objects 81 Working With LiveType Textures 82 Importing Graphics, Images, and Movies 83 Transforming Objects, Textures, and Imported Elements Chapter 7 87 Working With Effects and Keyframe Animation 88 Preset Effects 88 Applying Preset Effects 90 Adjusting the Timing of an Effect 93 Changing the Order of Effects 93 Duplicating Effects and Tracks 93 Modifying a Preset Effect 103 Creating a New Effect From Scratch Chapter 8 109 Previewing and Fully Rendering Your Titling Movie 109 Previewing Your Work 112 Optimizing Preview Performance 113 Rendering, Saving, and Exporting Your Titling Movie Chapter 9 117 Advanced Design Techniques 117 Words Within Words 119 Warping Shadows and Glows 121 Track Curves 123 Creative Use of Special Characters 126 LiveFonts and Layers 128 Creating Scrolls and Crawls UP01103TOC.fm Page 4 Monday, March 7, 2005 7:23 PMContents 5 Appendix A 131 Solutions to Common Problems and Customer Support 131 Frequently Asked Questions 133 Apple Applications Page for Pro Apps Developers 134 Calling AppleCare Support Appendix B 135 Creating and Editing EffectScripts 135 Header 135 Default Timing 136 Keyframes 140 Sample EffectScripts Glossary 143 Index 149 UP01103TOC.fm Page 5 Monday, March 7, 2005 7:23 PMUP01103TOC.fm Page 6 Monday, March 7, 2005 5:05 PM 7 Preface An Introduction to LiveType Welcome to LiveType, a special-effects titling application that’s powerful, easy to use, and completely versatile— whether you’re creating movie titles and credits, broadcast ads, or web banners. Producing dynamic video titles—titles that really pop—can be a painstaking process, fraught with manual adjustments and keyframe stacks daunting even to experienced animators. With LiveType, you can create phenomenal results, in the output format you require, with a fraction of the effort. How Does Titling Work? Traditionally, titling was the term for adding text to film. The evolution of digital graphics and video technologies has expanded the definition, which now includes just about any combination of text and images you want to add to a movie. Titling is the process of creating a digital overlay, which is added to edited footage in your nonlinear editor (NLE), or compositing program. LiveType is the design studio where you generate titles to import into Final Cut Pro. Alpha channel technology is the basis of titling. Most compositing and animation programs allow you to create art with an alpha channel. In addition, most NLEs use alpha channels they detect in an image or movie to properly lay the element over video. An alpha channel represents eight bits of grayscale pixel information in a 32-bit file. The eight grayscale bits determine which portions of the image to superimpose over other layers. White alpha-channel pixels make the superimposed image completely opaque, while black pixels make the overlay completely transparent, or invisible. Gray levels represent varying levels of opacity. LiveType automatically creates an alpha channel for your project when you render it with a transparent background.8 Preface An Introduction to LiveType A Realm of Creative Possibilities LiveType has revolutionized titling in two major ways. First, it introduced 32-bit LiveFonts, a new approach to text animation in which every character of a font is a separate, animated movie. Second, LiveType handles effects and animation with greater ease than any other titling application. Animated Fonts, Objects, and Textures Three types of animated media are included in LiveType:  LiveType objects are animated graphics.  LiveType textures are moving images used to fill backgrounds, text, or objects.  LiveFonts are complete, animated character sets. All of these elements move inherently, even before you apply motion paths and special effects to them. LiveType comes with dozens of LiveFonts and hundreds of objects and textures. What’s more, you can create your own animated fonts using the LiveType FontMaker utility, building characters using virtually any graphical object—from 3D animations and images created in Photoshop to video clips—and apply effects to them, just as you would to words. Effects Handling Effects in LiveType are handled as separate entities—“packages” encompassing movement, transformation, and timing parameters—that can be applied to any number of elements in the Canvas. You can take advantage of more than 100 customizable effects that come with LiveType, including fades, zooms, rotations, and motion paths. Or you can create your own styles by adjusting existing effects or building them from scratch. From an animation standpoint, LiveType is easier to work with than other titling applications, since one keyframe marker contains all the parameters for an element at a point in time, eliminating the complexity of long keyframe stacks. And powerful timing features allow you to control every aspect of your animation. In addition to basic functions such as loop, speed, and duration, LiveType allows you to sequence your effects. Sequencing lets you animate characters in a line of text individually, with their own timing elements, so you’re not constrained to blocks of text that fly around the screen as a unit. Whether you’re combining prebuilt elements or generating all the pieces yourself, you can create wholly original, eye-catching compositions with surprisingly little effort.Preface An Introduction to LiveType 9 Workflow for Creating Titles Video production is typically approached in layers from back to front, starting with shooting and editing the footage, then building in effects, then applying titles and sound. Likewise, your approach to title creation should be loosely approached from back to front. Of course, because the design process is fluid, there is no hard-and-fast prescription, but the following steps give you a sense of what’s involved for a typical project. Step 1: Configure the working environment  Set the output resolution, frame rate, and other project properties.  Set up the grid, guides, and rulers in the Canvas, according to your working preferences. Step 2: Apply a background, if any Step 3: Create elements (text or objects) in the Canvas, one by one  Position and shape a track for the element.  Add an element to the track.  Select a font.  Adjust attributes and apply styles to the element. Step 4: Animate the elements  Define the movie duration.  Apply effects and adjust the timing.  Customize the animation with keyframe adjustments. Step 5: Preview and fine-tune the movie Step 6: Render the final movie for compositing into your video Step 7: Export the movie to an alternative format, if needed You may be able to save considerable time by taking advantage of LiveType templates—project files provided with the software that offer many examples of titling formats. One might suit your needs with few changes, or you may find that certain elements within a template are useful, which you can copy into your own project. More about templates can be found in Chapter 2, “Setting Up a Project,” on page 31.10 Preface An Introduction to LiveType About This Manual Because LiveType is a creative tool, documentation can only go so far in describing its potential. This manual provides a detailed description of the LiveType interface, features, and functionality, and introduces you to the built-in resources and templates to give you a sense of the versatility of this product. In the end, you are limited only by your own creative vision, and the way to push the limits of LiveType is to jump in and start creating. This manual begins with a description of the interface, followed by a series of chapters that explain the tasks you’ll need to perform, as well as advanced techniques. Note: This user manual is written for people with a rudimentary understanding of film or video production. Experienced users will be quite familiar with all such terminology herein. Others will find that most terms are defined in context, and the glossary at the end of this manual may be helpful as well. LiveType Onscreen User Manual The LiveType onscreen user manual allows you to access information directly onscreen while you’re working in LiveType. To view the onscreen user manual, choose Help > LiveType User Manual. The onscreen user manual is a fully hyperlinked version of the user manual, enhanced with many features that make locating information quick and easy.  The home page provides quick access to various features, including Late-Breaking News, the index, and the LiveType website.  A comprehensive bookmark list allows you to quickly choose what you want to see and takes you there as soon as you click the link. In addition to these navigational tools, the onscreen user manual gives you other means to locate information quickly:  All cross-references in the text are linked. You can click any cross-reference and jump immediately to that location. Then, you can use the navigation bar’s Back button to return to where you were before you clicked the cross-reference.  The table of contents and index are also linked. If you click an entry in either of these sections, you jump directly to that section of the user manual.  You can also use the Find dialog to search the text for specific words or a phrase. LiveType Help also contains information about issues with third-party software and known bugs. This information is found in the Late-Breaking News section of LiveType Help.Preface An Introduction to LiveType 11 To access Late-Breaking News: m Choose Help > Late-Breaking News. Note: You must be connected to the Internet to download the Late-Breaking News file. Additionally, LiveType Help contains a link to the Creating LiveFonts PDF file. This document details the process of creating custom LiveFonts for use with LiveType. To access the Creating LiveFonts PDF file: m Choose Help > Creating LiveFonts. Apple Websites There are a variety of discussion boards, forums, and educational resources related to LiveType on the web. LiveType Website For general information and updates, as well as the latest news on LiveType, go to:  http://www.apple.com/finalcutpro/livetype.html Apple Service and Support Website For software updates and answers to the most frequently asked questions for all Apple products, including LiveType, go to:  http://www.apple.com/support You’ll also have access to product specifications, reference documentation, and Apple and third-party product technical articles. For LiveType support information, go to:  http://www.apple.com/support/livetype/index.html Other Apple Websites Start at the Apple homepage to find the latest and greatest information about Apple products:  http://www.apple.com QuickTime is industry-standard technology for handling video, sound, animation, graphics, text, music, and 360-degree virtual reality (VR) scenes. QuickTime provides a high level of performance, compatibility, and quality for delivering digital video. Go to the QuickTime website for information on the types of media supported, a tour of the QuickTime interface, specifications, and more:  http://www.apple.com/quicktime12 Preface An Introduction to LiveType FireWire is one of the fastest peripheral standards ever developed, which makes it great for use with multimedia peripherals, such as video camcorders and the latest highspeed hard disk drives. Visit this website for information about FireWire technology and available third-party FireWire products:  http://www.apple.com/firewire For information about seminars, events, and third-party tools used in web publishing, design and print, music and audio, desktop movies, digital imaging, and the media arts, go to:  http://www.apple.com/pro For resources, stories, and information about projects developed by users in education using Apple software, including LiveType, go to:  http://www.apple.com/education Go to the Apple Store to buy software, hardware, and accessories direct from Apple and to find special promotions and deals that include third-party hardware and software products:  http://www.apple.com/store1 13 1 The LiveType Interface The LiveType interface consists of four primary windows—the Canvas, the Inspector, the Media Browser, and the Timeline.  Canvas: This is where projects take shape. You use it to position text and objects, create motion paths, and view the results as you design.  Inspector: A toolbox of settings and parameters, including virtually every option for building and customizing your titling creations.  Media Browser: This area provides access to all the fonts, textures, objects, and effects you’ll use to create your titles.  Timeline: This is where you manage the frame-by-frame action of your titling projects. Animation keyframes are created and adjusted in the Timeline, allowing you to orchestrate the movement of your titling elements. Canvas Inspector Media Browser Timeline14 Chapter 1 The LiveType Interface The four windows float freely, and can be moved and resized to suit your working preferences. To restore the default layout of LiveType: m Choose Window > Apply Default Layout. Canvas The Canvas is your creative working environment, reflecting the output dimensions you configure in the Project Properties dialog. (See “Setting Project Properties” on page 34.) Whether you are working in HDTV, NTSC, PAL, or any other format, the Canvas is designed to help you lay out and view your titling project easily. About the Canvas Interface There are various interface elements and controls in the Canvas, outlined below. Background When you first open LiveType, the default checkerboard pattern in the Canvas represents a transparent background, allowing alpha channel titles to overlay video footage when composited in a nonlinear editor (NLE) such as Final Cut Pro. You can set the background as any combination of the following:  Transparent  Solid color  Animated texture or object  Still image  Movie Background (transparent) Action safe guidelines Track, showing multiple lines of text on one track Zoom pop-up menu Title safe guidelines Transport controlsChapter 1 The LiveType Interface 15 Backgrounds often cover the entire Canvas. However, when used with the matte feature in the Attributes tab of the Inspector, an element can appear to “punch through” an underlying element to reveal the background color, image, or movie. See “Creating a Matte” on page 72 for more about creating mattes. Tracks The dark blue horizontal line that appears in the default Canvas is a track. Tracks are the foundation of any LiveType composition. Every element of a project resides on a track. Tracks define:  The position of text and objects in the Canvas  The layering of elements  In some cases, the path taken by moving elements Tracks have two endpoints, and can have any number of “control points,” which are nodes that create angles and curves in the track. When more than one track is in the Canvas, only the endpoints of the selected, or active, track are visible. This identification is helpful when you’re applying attributes to a track. Action Safe and Title Safe Guidelines The green hairline boxes in the Canvas represent the “action safe” and “title safe” areas. The action safe area, defined by the outer line, is the extent of the screen where the image is readily visible, given the curvature of the cathode-ray tube (CRT). The title safe area, represented by the inner line, is the boundary beyond which text is not easily read. To turn the action safe and title safe guidelines off or on: m Choose View > Title Safe.16 Chapter 1 The LiveType Interface Canvas Zoom Pop-up Menu At the bottom of the Canvas is a pop-up menu for changing the magnification of the Canvas. To change the Canvas zoom, do one of the following: m Open the Canvas zoom pop-up menu at the bottom of the Canvas and choose one of the magnification options. m Choose Fit to Window from the Canvas Zoom pop-up menu, then resize the Canvas window to a new magnification. m Choose View > Zoom In or Zoom Out. m With the Canvas active, use the Command-Z keyboard shortcut for Fit to Window. m With the Canvas active, use the Command-+ or Command-– keyboard shortcut to zoom in or out. Transport Controls The transport controls allow you to generate a RAM preview of your project so you can preview your titling movie right in the Canvas. When you click the Play button, LiveType renders each frame into RAM memory. This feature is referred to as a RAM preview. Canvas Zoom pop-up menu Previous frame Play Next Frame LoopChapter 1 The LiveType Interface 17 To render a RAM preview of your project in the Canvas: 1 Click the Play button (or press the Space bar when the Canvas or Timeline is active). The preview renders each frame, then runs through the preview in real time. 2 Stop the preview by clicking anywhere in the Canvas. The Play icon turns into a Pause icon when the RAM preview is playing. The Loop button is a toggle that gives you the choice of a single run-through or repeating the preview in a continuous loop. See Chapter 8, “Previewing and Fully Rendering Your Titling Movie,” on page 109 for more about previewing your work. Customizing the Canvas Most Canvas settings can be customized from the View menu, allowing you to configure guidelines and magnification, and choose which elements appear in the Canvas. The grid, rulers, and guides are helpful for precisely aligning and positioning elements in the Canvas. To show the rulers or the grid: m Choose View > Rulers. m Choose View > Grid. You can set the number of pixels between each grid line in the Project Properties dialog. Grid Ruler for vertical guides Ruler for horizontal guides18 Chapter 1 The LiveType Interface To customize the grid: 1 Choose Edit > Project Properties. 2 In the Ruler and Grid Settings area at the bottom, enter a new value in the Grid Width field. To add a guide to the Canvas: m Click inside one of the rulers to insert a guide marked by its horizontal or vertical pixel position. To add crosshairs to the Canvas: m Click inside one of the rulers and drag the pointer onto the Canvas. To remove guides from the Canvas, do one of the following: m Drag guide markers off either end of the ruler. m Choose View > Clear Guides, which removes all guides. You can isolate a single track and display all other elements as bounding boxes— rectangles that roughly show the size, position, and orientation of an element. This option is useful for cleaning up the Canvas as you work on a single track, and it saves preview-rendering time, because only one item of your composition is being rendered. Guide marker showing pixel position Crosshair guideChapter 1 The LiveType Interface 19 To isolate a single track in the Canvas: m Select the track you want to continue working on, then choose View > Selected Only. Revert to the normal view by choosing View > Selected Only again. The Proxy Frame Only option in the View menu–which applies only when you’re using installed LiveType media—renders LiveFonts, textures, and objects as proxy frames in the Canvas, essentially freezing their inherent animation. Particularly when the animated element has highly variable content from frame to frame (such as Particles objects, which contain few if any pixels in the beginning and ending frames), the proxy frame is easier to work with, because it shows a more representative shape of the object regardless of the playhead position. Bounding boxes show the size and position of deselected elements. Choose View > Selected Only to view only the contents of the selected track.20 Chapter 1 The LiveType Interface Inspector The Inspector is your toolbox for transforming elements—text, objects, or images. There are unlimited combinations of parameters and attributes you can use to make your titles dynamic and original. The Inspector consists of a text-entry box and Live Wireframe Preview at the top of the window, and five tabs of parameters. Inspector settings always apply to the track, character, or effect that is currently selected in the Canvas or Timeline. Text-Entry Boxes There are two areas in the Inspector where you can add text to a track. One of these is in the upper-left corner of the Inspector. Because this text-entry box is visible no matter which Inspector tab is selected, it is a convenient way to identify the active track, as well as to add or change the text on a track, as you can type directly into it. The textentry box at the bottom of the Text tab is larger, making it easier to insert and edit larger amounts of text. The text-entry boxes also allow you to select individual letters or words on a track. When you highlight text in the text-entry box, those characters are selected in the Canvas. This is particularly useful when the text you want to modify is obscured in the Canvas by other elements. Text-entry box Live Wireframe Preview Inspector tabs Text-entry box (in the Text tab only)Chapter 1 The LiveType Interface 21 Live Wireframe Preview In the upper-right corner of the Inspector, the Live Wireframe Preview continually plays your titling movie, with small bounding boxes indicating the movement of each character or object. This feature gives you a quick indication of how your adjustments have changed the overall animation, without rendering a full preview with every change you make. To freeze or unfreeze the Live Wireframe Preview: m Click inside the preview area. Inspector Tabs There are five tabs in the Inspector.  Text tab: This is where you enter text and adjust the size, alignment, and spacing of text on the active track. Preview playhead Small bounding boxes depict the movement of the Canvas elements. Click to turn the preview on or off. Text tab settings22 Chapter 1 The LiveType Interface  Style tab: This tab provides options for the Shadow, Glow, Outline, and Extrude treatments, which can be applied to text or objects. These are often used to add depth and highlight the text or object, although a wide variety of graphical outcomes are possible.  Effects tab: This tab lists the effects that have been applied to the active track, and is used to view and change effect parameters at any point in your titling movie. Effects are combinations of movement and transformation that can be applied to any track. The On column of the Effects tab allows you to turn an effect off or on for individual characters on the track. Style tab settings Effects tabChapter 1 The LiveType Interface 23  Timing tab: Timing parameters for tracks and effects are controlled in this tab. While the Timeline provides a frame-by-frame diagram of tracks and effects with their associated keyframes, the Timing tab is a single pane that allows you to adjust the overall timing and modify the parameters of your animation. Some timing adjustments are made more easily by moving elements in the Timeline, rather than entering values in the Timing tab. However, the Timing tab gives you access to the full range of timing variables, as well as effect parameters that let you fine-tune your animation, creating exactly the look you want. Timing tab24 Chapter 1 The LiveType Interface  Attributes: This is where you assign a variety of attributes—opacity, blur, scale, offset, rotation, and color—to elements in the Canvas. Attributes can be applied to entire tracks or individual characters on a track. The Attributes tab also contains options for creating a matte effect, in which an element appears as a cut-out window that reveals the element below it. A simple line of text, for example, can be matted to a movie clip, which essentially “fills” the text. The Matte to Texture option lets you fill track contents—even individual characters—with an animated texture, without having to add the texture to your project as a separate element. Matte settings are variables for creating cutouts and textured fills. Glyph settings include attributes such as the shape, color, and position of text and objects. Attributes tab in the Matte pane Attributes tab in the Glyph paneChapter 1 The LiveType Interface 25 Media Browser Most of the installed resources available for your titling projects are available through the Media Browser—except for LiveType templates and images and movies you import from other sources. There are various tabs representing different elements installed on your computer: LiveFonts, system fonts, textures, objects, and effects. Using the Media Browser, you can scroll through and view representations of all these elements before you apply them to your project. The Media Browser preview is the only way to see how LiveType media—LiveFonts, textures, and objects—move and transform until you install the full data file onto your computer. When you first apply one of these elements to the Canvas, a single representative frame is displayed, not the entire animated sequence. Installing the data component allows you to see a true representation of the LiveFont in each frame of your movie. See “LiveType Media Files” on page 28 for more about LiveType file management. Browser preview Tabs of media and effects26 Chapter 1 The LiveType Interface Timeline The Timeline depicts the frame-by-frame orchestration of your titling project, and provides many tools for designing the movement and timing of your titles. The Timeline allows you to do the following:  Set the timing and duration of tracks and effects  Manage the track order, or layers  Group tracks to maintain their relative position  Enable and disable tracks and effects  Work with keyframes to customize your animation  Select specific frames to view or adjust  Set markers to render only a portion of your movie for previews or final output About the Timeline Interface The following are the interface elements and controls in the Timeline. Project Tabs Tabs at the upper-left corner of the Timeline indicate which projects are currently open, and which one is active. Playhead, Timecode, and Frame Ruler The playhead and timecode on the frame ruler indicate which frame is showing in the Canvas. The playhead moves along the frame ruler when you play your project, and it can be dragged to any given frame. To view a specific frame, do one of the following: m Drag the playhead to the desired frame. m Click a frame in the frame ruler. The Canvas always reflects the frame under the playhead. Playhead Timeline zoom slider Project tab Grouping buttons Keyframe Background bar Timecode Enable/Disable buttons Track Effect Frame ruler Render Selection Out pointChapter 1 The LiveType Interface 27 Render Selection Markers The In Point and Out Point markers in the frame ruler allow you to determine the portion of your movie you want to render. Using these markers, you can:  Save time rendering previews when you don’t need to see the entire movie  Choose the precise number of frames you want to include in your final output To change the render selection, do one of the following: m Drag the In Point and Out Point markers in the frame ruler. m Position the playhead and press the I key on your keyboard to set the Render Selection In Point, or the O key to set the Render Selection Out Point. The Timeline must be active for these hot keys to work. As you constrain the range of frames to be rendered, the information box in the upperleft corner of the Timeline reflects the modified duration and number of frames. Note: To quickly locate the Out Point marker when it is beyond the end of the visible Timeline, move the Timeline zoom slider all the way to the right. Tracks and Effects Tracks are numbered according to their layer position in the left column of the Timeline, and Track 1 is always the top layer. Effects are depicted as separate bars underneath the track they apply to. An effect may extend for the entire duration of the track, or only a portion of it. One track may have several effects applied to it, in sequence or overlapping. Background Bar Any item that falls below the background bar is a background element. You can drag the background bar up or down to any position between tracks in the Timeline. For more information, see “About the Background Bar” on page 43. Keyframes The basis of most digital animation, keyframes contain the parameters that elements in the Canvas reflect at a specific point in time. When a movie is rendered, LiveType interpolates the movement of the elements in between keyframes for smooth, continuous motion. When an effect is increased in duration, or stretched, the keyframes spread out with it, and the effect takes longer to complete. See Chapter 7, “Working With Effects and Keyframe Animation,” on page 87 to learn more about keyframes. Grouping Buttons Grouping buttons let you group tracks together in the Canvas, locking their relative position while allowing you to move the group as a unit.28 Chapter 1 The LiveType Interface Enable/Disable Buttons The Enable/Disable buttons turn tracks and effects off or on. When a track is disabled, its contents are removed from the Canvas, although the blue track line remains. Disabled tracks are not rendered in previews or movies. Similarly, effects can be disabled. Timeline Zoom Controls Typically you use the zoom controls to adjust the amount of time represented in the Timeline window. This is helpful to do while working with timing a long or complex composition. The main zoom control is the Timeline zoom slider, which zooms in and out around the playhead as you drag. You can also use the Command-+ or Command-– keyboard shortcut to zoom in or zoom out on the playhead when the Timeline is active. Another helpful command is Shift-Z, which adjusts the Timeline to show the entire project at once. LiveType Media Files LiveType includes hundreds of media and effects files, which are the resources available to you within the Media and Template Browsers. Animated files include LiveFonts, objects and textures. Preset effects and templates, as well as various other LiveType resources, are also included with the application. These files are collectively known as LiveType media files. LiveType now uses a single file format for media such as LiveFonts, textures, and objects, but media using the earlier “pair format” is still supported. Shortcuts and Hot Keys The LiveType interface includes numerous menu items and shortcuts to help you use the application easily and efficiently. It’s important to note that the function of these options depends on which LiveType window is active. For example, when the Canvas is active, the arrow keys nudge the active track in small increments. However, when the Timeline is active, the right and left arrow keys advance the playhead or move it back one frame.Chapter 1 The LiveType Interface 29 Locating LiveType Media Files When you install LiveType, a folder hierarchy is placed in the following location: Library Application Support/LiveType/. This is where LiveType looks first for media files such as LiveFonts, objects, textures, effects, images, movies and templates. LiveType media files can also be installed on other hard disks including a network server. You can assign any location for media files from the Preferences dialog. About Installing LiveType Media Files The LiveType installation process allows you to install LiveType media files in any location. For more details concerning installing LiveType and the LiveType media files, see the Installing Your Software document that is enclosed with the installation discs. Managing LiveType Media Files Any element in the LiveFonts, Textures, Objects, and Effects tabs of the Media Browser has a corresponding media file, which contains the components needed to work with LiveType. Once these media files are installed in the /Library/Application Support/ LiveType folder, you can move them to a different disk. To use LiveType media that is located outside the application support folder: m Assign the location of the media files from within LiveType using the Preferences dialog. Choose LiveType > Preferences. Note: To use LiveType media that is located outside the application support folder, assign its location from within LiveType using the Preferences dialog. If you have media installed from a previous version of LiveType, the Media Browser reads “Yes” or “No” in the Installed column for that media which indicates whether or not the media files are installed. This convention only applies to earlier “file pair” formats. New content comes in the form of media files that appear in the Media Browser with a double dash in the Installed column indicating they are installed. The Install and Uninstall buttons in the lower-left corner of the Media Browser do not apply to the newer content, only to LiveType media files from previous versions of the application. Media file types Media filenames Media file contents Effects LTFX Contains effects files and sample movies for each effect. LiveFonts LTLF Animated font characters Objects .LTOB Pre-rendered animations with an alpha channel Templates LTTM LiveType projects Textures LTTX Full screen animated backgrounds. These animations can also be matted to any font character or element on the LiveType Canvas.30 Chapter 1 The LiveType Interface Creating Custom Categories for LiveType Media files You can create custom categories for LiveType Media by simply creating a new folder within the Media folder, such as LiveFont/My folder/My font. LiveType only recognizes one folder level after the original media category. You can move “file pair” media files from previous versions of LiveType to another disk, but they must be in the same folder hierarchy that they were previously located in. Using Imported Files When you use graphics or movies from other sources in your project, LiveType needs to refer to the source files for these external elements. Therefore, once you’ve placed an image or movie, it’s best not to move or rename the source file. The Images folder in the LiveType folder hierarchy is a convenient place to store images associated with your projects.2 31 2 Setting Up a Project The most important step as you begin any LiveType project is to configure the project properties. As tempting as it may be to jump right in and start designing, you should define your output parameters and save the project to disk at the outset, to be sure your titles are generated at the size and resolution you need. If you go ahead and generate a titling movie without initially configuring the project, you’re bound to run into trouble. Although these settings can be changed at any time, a titling composition created for standard broadcast, for example, will fill only a portion of the screen if it’s changed to high definition format after the fact. First, you need to open a new project. You have two options:  Start with a LiveType template.  Start with an existing LiveType project you’ve already created. Templates LiveType includes dozens of templates, which are LiveType project files organized by category. You can use templates in several ways:  As the starting point for your own creations  As repositories of preconfigured elements you can paste into your own projects  As a resource for sparking ideas and seeing what’s possible with LiveType The templates comprise many types of prebuilt projects, all of which you can revise for your own purposes.32 Chapter 2 Setting Up a Project To open a template: 1 Choose F