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Figure 3 14. Information flow in Hello World
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CHAPTER 3: Interface Builder
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The skeleton for this code is already in place. Here is HelloController.h (the header comments are omitted).
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#import <Cocoa/Cocoa.h> @interface HelloController : NSObject { } @end
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You need to create an outlet as the place where the message is sent (the label) and an action (sayHello) to tell the controller how to send that message. Here are the declarations you need to add (see the bold text in Listing 3 1):
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Listing 3 1. Changes to HelloController.h #import <Cocoa/Cocoa.h> @interface HelloController : NSObject { IBOutlet NSTextField *destinationTextField; } - (IBAction)sayHello:(id)sender; @end
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This code is saying that the controller has an outlet called destinationTextField and an action called sayHello. Now for the implementation: Turn to HelloController.m remember, you can use the little gray counterpart button at the top right of the Editor pane and make it look like this (add the code in bold text in Listing 3 2).
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Listing 3 2. Changes to HelloController.m #import "HelloController.h" @implementation HelloController -(IBAction)sayHello:(id)sender { [destinationTextField setStringValue:@"Hello, World!"]; } @end
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Now, a really important step here is to save both of the files you have modified. Apart from being a good practice to save as you go, if you don t save the files the next part won t work. And the next part is to make the connections between the user interface objects (the view) the model (a piece of text) and the controller (your HelloController class). Go back to Interface Builder. You need to create an object to represent the HelloController. Find NSObject in the Library window and drag it into the Document window. The next few steps are absolutely key to getting your application wired up correctly. First, tell Interface Builder that this new object is, in fact, a HelloController. Make sure that the new object is selected in the Document window, and choose the Object Identity tab in the Inspector (it has a small i icon). Choose the Class dropdown menu and set it to HelloController (Figure 3 15).
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CHAPTER 3: Interface Builder
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Figure 3 15. Setting the controller object type in Interface Builder
Now Interface Builder knows that your new object is an instance of the HelloController class that you described in Xcode; it has even helpfully renamed the object to HelloController. NOTE: If you don t see HelloController as an item in the class list, this probably means that you haven t saved your HelloController.h file. Next, you need to connect the outlet to the controller. Remember from earlier that the controller has a destinationTextField. That is the label in the main user interface window. To connect the two, Control-click or right-click on the HelloController in the Document window. A small head-up display (HUD) panel will appear. Mouse down on the empty circle to the right of the destinationTextField outlet, and drag a line over to the label. Release the mouse button when the label control highlights. You have just told the HelloController that it has an outlet pointing to the label on the main window. You can confirm the connection by selecting the HelloController in the Document window, and checking its outlets settings (either by right-clicking again and seeing the list in the HUD, or by looking in the Connections tab of the Inspector (Figure 3 16 shows both ways of checking).
CHAPTER 3: Interface Builder
Figure 3 16. Checking that the connection is correct
So that is where the Controller is sending a message. But what message, and what causes the message to be sent Clicking the button tells the Controller to send the message by invoking the action method that you created in Xcode (sayHello:). So you need to connect the button to the Controller. Right-click on the button to bring up its HUD, mouse down on the circle next to selector under Sent Actions, then drag a line to the HelloController (remember we are sending a message from the button to the Controller). When the HUD appears, select sayHello: . You can check that the connection has worked in the same way as before, in the HUD for the button or the Connections tab of the Inspector. Save the NIB file and quit Interface Builder. Return to the Xcode Workspace; your application is complete. All that remains is to Build and Run (click the big green button in the toolbar). Assuming all went well, you will see a series of build messages in the status bar and then the running Hello World program (Figure 3 17).
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