The Interface Builder document contains four items:

A File’s Owner proxy object. The File’s Owner object is actually the UIApplication instance—File’s Owner are discussed later, in “File’s Owner.”

A First Responder proxy object. The First Responder is not used in this tutorial but you can learn more about it by reading “Event Handling” in iPhone Application Programming Guide.

An instance of HelloWorldAppDelegate set to be the application’s delegate. Delegates are discussed in the next section.

A window. The window has its background set to white and is set to be visible at launch. It’s this window that you see when the application launches.

After the application has finished launching, you can perform additional customization. A common pattern—and the one you’ll follow in the next chapter—is illustrated in this diagram:

When the application object has completed its setup, it sends its delegate an applicationDidFinishLaunching: message. Rather than configuring the user interface itself, the delegate typically creates a view controller object (a special controller responsible for managing a view—this adheres to the model-view-controller design pattern as described in “Model-View-Controller”). The delegate asks the view controller for its view (which the view controller creates on demand) and adds that as a subview of the window.

Recap

In this article you created a new project and learned about how the application launch process works. In the next chapter, you’ll define and create an instance of a view controller.

Adding a View Controller

In this application you’ll need two classes. Xcode’s application template provided an application delegate class and an instance is created in the nib file. You need to implement a view controller class and create an instance of it.

Adding a View Controller Class

View controller objects play a central role in most iPhone OS applications. As the name implies, they’re responsible for managing a view, but on iPhone OS they also help with navigation and memory management. You’re not going to use the latter features here, but it’s important to be aware of them for future development. UIKit provides a special class—UIViewController—that encapsulates most of the default behavior you want from a view controller. You have to create a subclass to customize the behavior for your application.

>> In Xcode, in the project organizer select either the project (HelloWorld at the top of the Groups and Files list) or the Classes group folder—the new files will be added to the current selection.

>> Choose File > New File and in the New File window. Select the Cocoa Touch Classes group, then select UIViewController subclass. In the Options section, choose only With XIB for user interface.

Note: If you don’t see the “With XIB for user interface” option, make sure you have installed version 3.2 of the iPhone OS SDK—Xcode should show version 3.2.2 or later.

Selecting “With XIB for user interface” means that Xcode creates a nib file to accompany the view controller, and adds it to the project. (Nib files are discussed in detail in the next chapter.)

>> Click Next, and in the following screen give the file a new name such as MyViewController (by convention, class names begin with a capital letter). Make sure that both the .m and .h files are created and that the files are added to your project, as shown here:

>> Press Finish and make sure that the files were added to your project.

If you look at the new source files, you’ll see that stub implementations of various methods are already given to you. These are all you need for the moment; the next task is to create an instance of the class.

In next article we will learn about Adding a View Controller Property

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