Tracing the iOS Application Life Cycle

To help you get a sense for where your “work” in developing an iOS application fits in, it helps to look at the application life cycle. Figure 4.2 shows Apple’s simplified diagram of the life cycle.

Figure 4.2 The life cycle of a typical iOS application.

Let’s try to put some context around what you’re looking at, starting on the left side of the diagram. As you’ve learned, UIKit is a component of the Cocoa Touch that provides much of the foundation of iOS applications: user interface management, event management, and overall application execution management. When you create an application, UIKit handles the setup of the application object via the main and UIApplicationMain functions, neither of which you should need to touch.