iPhone App Development: The Missing Manual

Open the Guide Book

Begin your tour by opening the guidebook: Locate the Flashlight_Pro.xcodeproj project file that you downloaded from the Missing CD page, and double-click its icon to open it with Xcode. Make sure that the main Flashlight Pro group and the Application Delegate subgroup are both open, as shown in Figure 6-1.

Figure 6-1. Throughout this chapter, you use the Groups & Files list in Xcode to find the code discussed on these pages. This figure shows Flashlight_ProAppDelegate.m selected in the list and viewed in the editor. To make the editor fill the right-hand side of the window, use View→Zoom Editor In (⌘-Shift-E). You'll learn more about the first line of code (selected) on below.

As was noted in the list on the previous page, the application delegate is the first place your code is executed, so that's where this tour starts.

Flashlight_ProAppDelegate

There's really only one method that matters in this class's implementation: –applicationDidFinishLaunching:. And even though it has only a few lines of code, a lot is going on here.

UIApplication

In Flashlight_ProAppDelegate.m, you see the UIApplication class for the first time. One instance of this object is always available, and it allows you to query and configure the state of your application within the iPhone OS.

In this instance, the property that allows the screen to dim and turn off is disabled:

[[UIApplication sharedApplication] ...