Exploring the Phone Code Through the Debugger

We will use the Eclipse debugger, set breakpoints, and inspect class members in the running application to observe what is going on inside this example. The use of the debugger with Android is described in Chapter 5. If you have not used a debugger before, don't worry: we will use a limited set of debugging capabilities here to observe a program that works correctly. Just follow the steps in this section and let the debugger show you what is happening.

First, we will set a breakpoint where we want to start observing what is happening inside the application. To set a breakpoint, double-click on the left margin of the view that shows the program code in Eclipse. A blue dot will appear. If you change your

Satelite Phone
Figure 14-2. Dialer starts

mind and decide not to insert a breakpoint, double-click again on the blue dot, and it will disappear.

All we want is to stop execution of the program at the point where we want to start inspecting what happens to the members of this instance of the dialing class. To do this, set a breakpoint on line 21 of the program. You can tell which line you are on by clicking a line in the program. In the status bar at the bottom of the Eclipse window, you will see two numbers separated by a colon. The first number is the line number where you just clicked, and the second number is the character position on that line where the insertion point is right now.

Start the application with the debugger by selecting Run ^ Debug, and when the "Debug as" dialog appears, select Android Application.

The program will stop at the breakpoint, after the Android emulator appears on your screen but before the appearance of the dialer shown in Figure 14-2. Eclipse will switch to a debug perspective: a set of views configured for debugging a program instead of editing it. Eclipse will ask if you want to switch perspectives the first time you run the

Figure 14-3. Eclipse debugger stopped in call method

debugger; you can save your answer if you want Eclipse to do the same thing each time you start debugging.

In the debug perspective, the view displaying the program code will show a small arrow overlapping the blue dot in the left margin. This line of code will be highlighted. The program has stopped before executing the Java bytecodes corresponding to the Java source code on this line of the program.

Figure 14-3 shows the Eclipse window in debug perspective with contents similar to those that should appear on your screen. The main information to look for is that the program stopped executing on the line where you set the breakpoint.

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