Lập trình Wrox Professional Xcode 3 cho Mac OS part 35 pps

When you release the mouse button, a menu appears with every outlet and action connection that ’ s possible between those two objects. Select the outlet or action and the connection is complete. FIGURE 13-38 There ’ s a limitation when making quick connections from Cocoa Touch objects. When you create an action connection, the action is always connected to the Touch Up Inside event. In other words, you can ’ t use a quick connection to select both the event to connect to and the action message to send. Use the pop - up connections panel if you need to connect an action to some event other than Touch Up Inside. The real power of connections and actions emerges when you defi ne your own outlets and action messages. This is explained in the next section. CUSTOM CLASSES Interface Builder would only be mildly useful if all it could do was create, confi gure, and connect instances of the predefi ned framework objects found in the library palette. The power of Interface Builder explodes when you can defi ne your own classes, outlets, and actions, and then use Interface Builder to create instances of your custom objects, confi gure them, and then connect them just like any other nib document object. Using Interface Builder you can: Add instances of your custom classes to a nib document. Defi ne outlets in your custom classes that will be recognized by Interface Builder. Defi ne action methods in your custom classes that will be recognized by Interface Builder. Interface Builder recognizes when a nib document belongs to an open Xcode project. It then interfaces with Xcode to extract information about your class defi nitions and incorporate that into the document. It does this quickly, quietly, and transparently in the background. All you have to do is defi ne your class. By the time you ’ ve saved your class fi les and switched to Interface Builder, your class defi nitions will have been assimilated and are ready to instantiate, confi gure, and connect. ➤ ➤ ➤ Custom Classes ❘ 269 c13.indd 269c13.indd 269 1/21/10 3:37:53 PM1/21/10 3:37:53 PM Download at getcoolebook.com 270 ❘ CHAPTER 13 INTERFACE BUILDER Save your source fi les! Interface Builder only considers class defi nition fi les that have been saved to disk. Get into the habit of saving all fi les (Option+Command+S) before switching from Xcode to Interface Builder. This ensures that Interface Builder has the most current knowledge about your project’s class defi nitions. If a class or property doesn’t appear in Interface Builder, make sure your source fi les don’t have any syntax errors. Also make sure the Synchronize With Xcode option is checked in the Interface Builder preferences. Creating an Instance of a Custom Class You can add an instance of practically any class you ’ ve defi ned in your project to a nib document. To create an instance of a class, follow these steps: 1. Defi ne the class in Xcode. 2. Save the interface fi le(s) that defi ne the class. 3. In Interface Builder, fi nd the generic superclass object for your class in the library palette and create an instance of it. 4. Select the new object. 5. In the identity inspector, change the class of the object from its generic class (for example, NSObject) to your specifi c class (such as MyObject). Figure 13 - 39 shows the class of a generic NSObject being changed to MyAppDelegate, a custom class defi ned in the active Xcode project. At run time, an instance of your class is created instead of the generic object that was in the library palette. The library palette object you choose will depend on the superclass of your custom object. In general, follow this rule: choose the most specifi c class in the library palette that your custom class inherits from. For example, if your class is a custom subclass of NSTokenField, then create an NSTokenField object before changing its class to yours. Interface Builder understands that your object is a subclass of NSTokenField and will present all of the attributes, connections, and actions defi ned by its superclasses (NSTokenField, NSTextField, NSControl, and NSView), in addition to any outlets and action methods that your subclass defi nes. FIGURE 13-39 c13.indd 270c13.indd 270 1/21/10 3:37:55 PM1/21/10 3:37:55 PM Download at getcoolebook.com The library palette provides a short list of truly generic classes that — as themselves — don ’ t do much of anything useful. They are included in the library palette solely so you can create custom subclasses of them: GENERIC LIBRARY OBJECT CLASS Object or External Object NSObject View Controller NSViewController or UIViewController Custom View NSView View UIView Create an (External) Object when you subclass NSObject directly, or subclass any class that isn ’ t represented in the library palette. Anything means anything. Interface Builder will let you change the class of a generic NSObject instance to any class that exists, even ones defi ned in the frameworks. There’s no NSMutableArray object in the library palette, but there’s nothing stopping you from creating a generic Object instance, changing its class to NSMutableArray, and connecting it to an outlet. At run time, the nib document will gladly create and connect an instance of NSMutableArray. The most obvious applications of custom objects in a nib document are to: Create a controller object and connect it to all of its view objects. Create a custom delegate object and connect it to the delegate outlet of whatever objects (application, windows, tables, and so on) it should augment. Create custom subclasses of NSView or UIView and position them in superviews. I ’ m sure you can think of a million other uses. The basic principle is this: If you need to create an object that will connect to, or be connected from, other objects in a nib document, consider creating the object in the nib document. Now that you know how to create instances of your own classes, or replace instances of library objects with your own custom subclasses, you ’ ll want to start creating custom connections. To do that, you need to defi ne outlets and actions in your class. Adding Custom Outlets to Your Class Adding outlets to your own class is simple: 1. Declare a settable property (or instance variable) that stores an object pointer. 2. Include the IBOutlet modifi er in the property ’ s type. ➤ ➤ ➤ ➤ Custom Classes ❘ 271 c13.indd 271c13.indd 271 1/21/10 3:38:00 PM1/21/10 3:38:00 PM Download at getcoolebook.com 272 ❘ CHAPTER 13 INTERFACE BUILDER All IBOutlet marked properties will appear as outlets in the object ’ s connections inspector. In Figure 13 - 40, the class MyAppController declares an aboutWindow property that refers to an NSWindow object. FIGURE 13-40 If you ’ re using Objective - C 2.0, the preferred place to declare a property as an IBOutlet is in the @property directive, as was shown in Figure 13 - 40. You can still use the IBOutlet type modifi er in the instance variable declaration if you ’ re not using Objective 2.0 or do not include a @property directive. Interface Builder will recognize either. I should note that the IBOutlet type really isn ’ t a type; it ’ s just tag for Interface Builder. As of this writing, IBOutlet is a preprocessor macro that ’ s replaced with nothing at compile time. Renaming a property by editing its declaration can confuse Interface Builder. For example, if you renamed aboutWindow to creditsWindow after having connected aboutWindow to the NSWindow object in your nib document, the nib document will now contain a connection to a non-existent property. (In Interface Builder this will appear as a connection with a warning symbol next to it.) Rename outlet properties and action methods using the Refactoring tool (see Chapter 10), which can fi nd and rename any nib document references as well. Adding Custom Actions to Your Class Creating actions is about as simple as creating outlets: 1. Defi ne a method that conforms to the prototype — (void) anyMethod :(id) sender . a. The method must have a void return type. b. The method should expect a single object reference as its only parameter. c13.indd 272c13.indd 272 1/21/10 3:38:06 PM1/21/10 3:38:06 PM Download at getcoolebook.com 2. Replace the return type in the declaration with IBAction , as in - (IBAction) myAction :(id) sender . In Figure 13 - 41, an action method has been added to MyAppDelegate. The action appears in the connections inspector, where it can be connected to view objects. In this case, the button ’ s action is confi gured to send MyAppDelegate a - closeAboutWindow: message when the user clicked the button. FIGURE 13-41 When your object receives an action, the sender parameter refers to the object that sent the message, providing it some context. In the case shown in Figure 13 - 41, sender refers to the “ OK ” NSButton object the user clicked. Note that this is a convention of the Cocoa framework, it ’ s not a strict requirement. If you send action messages yourself, you can pass some other object, or even nil , as you see fi t. Many action methods simply ignore the sender parameter. Initializing Custom Objects at Run Time For the most part, nib fi les contain archived (serialized) versions of Cocoa objects, but the nib fi le loading mechanism makes some concessions, and relaxes a few of the normal rules of object archiving in order to make the nib fi le content as fl exible and convenient as possible. Specifi cally: Custom objects in a nib fi le are not required to conform to NSCoding protocol. Most custom objects are initialized using a simple — init method, rather than the formal — initWithCoder: used to decode archived objects. This means that your custom objects don ’ t have to conform to NSCoding in order to be instantiated from a nib fi le. It also means that any object that can be validly constructed with [[ Class alloc] init] can be added to a nib fi le. ➤ ➤ Custom Classes ❘ 273 c13.indd 273c13.indd 273 1/21/10 3:38:17 PM1/21/10 3:38:17 PM Download at getcoolebook.com 274 ❘ CHAPTER 13 INTERFACE BUILDER The following table describes exactly how objects in a nib document are constructed at run time: OBJECT TYPE DESCRIPTION INITIALIZER Custom View Objects A custom subclass of NSView . - initWithFrame: Non - View Custom Objects A custom subclass of NSObject that is not a subclass of NSView. - init Interface Builder Classes Any class that appears in the library palette, or a custom subclass of an object that appears in the library palette. - initWithCoder: Constructing custom view objects with - initWithFrame: makes them compatible with the normal programmatic initialization of NSView objects ( - initWithFrame: is NSView ’ s designated initializer). All non - view custom objects are constructed with the standard - init message. This means that you don ’ t have to make your class conform to NSCoding in order to include it in a nib fi le. The objects defi ned in the Interface Builder palette all conform to NSCoding and are initialized using the standard decoding method - initWithCoder: . The attribute values that you set in the inspector panels are decoded from the archive data stream. If you create a custom subclass of an Interface Builder object that ’ s constructed with - initWithCoder: , your class will initialize itself with - initWithCoder: too. That ’ s the only way that attributes set for its superclasses can be read at run time. Custom NSObject subclasses can be initialized with - init because there are no editable properties for custom classes — only outlets and actions. Nothing needs to be read from the archive stream during initialization. After the objects in the nib fi le are constructed, two more things happen: 1. All of the connections are set. 2. Every object receives an - awakeFromNib message. If your object needs to perform any additional initialization, especially any initialization that depends on connections, it should implement a - (void)awakeFromNib method. PLACEHOLDER OBJECTS A subject I ’ ve been avoiding is what those other, mysterious, objects in your nib document — like File ’ s Owner and First Responder — are. These are special placeholder objects . They represent objects that will exist before the nib document is loaded. Now that you understand connections and custom objects, explaining the role of placeholder objects is simple. Placeholder objects allow you to create connections between the objects in your nib document and objects that already exist in your application. This allows you to create connections to objects outside the set of objects in the nib document. c13.indd 274c13.indd 274 1/21/10 3:38:19 PM1/21/10 3:38:19 PM Download at getcoolebook.com . to a nib fi le. ➤ ➤ Custom Classes ❘ 2 73 c 13. indd 273c 13. indd 2 73 1/21/10 3: 38:17 PM1/21/10 3: 38:17 PM Download at getcoolebook.com 274 ❘ CHAPTER 13 INTERFACE BUILDER The following table describes. and connect. ➤ ➤ ➤ Custom Classes ❘ 269 c 13. indd 269c 13. indd 269 1/21/10 3: 37: 53 PM1/21/10 3: 37: 53 PM Download at getcoolebook.com 270 ❘ CHAPTER 13 INTERFACE BUILDER Save your source fi les!. any outlets and action methods that your subclass defi nes. FIGURE 13- 39 c 13. indd 270c 13. indd 270 1/21/10 3: 37:55 PM1/21/10 3: 37:55 PM Download at getcoolebook.com The library palette provides