Exception Handling

What if something goes wrong? The code in the call method that starts the dialer is wrapped in a try/catch block. The catch statement contains a line of code that logs an error if the startActivity method throws an exception of the type ActivityNot FoundException. If a method can throw an exception that indicates an error, the call to that method should be in a try/catch block that catches that type of exception. In this case, we use Android's logging facility to record the error.

We do not catch all exceptions, because unexpected exceptions indicate failures a program cannot, in general, recover from.

Let's make an exception happen. We can do this by removing part of the data needed to have the startActivity method call work correctly. Comment out line 22 of the code, as shown:

// callIntent.setData(Uri.parse("tel:978555l212"));

Now make some changes to breakpoints. Clear the breakpoint on line 21, and set a breakpoint on line 25, where, in the catch clause, the method of the Log class is called to log the caught exception. Use the Run —• Debug command again to start the program.

This time you will see execution stop at the new breakpoint you set. You will also see that an exception has been thrown. The Debug view in Eclipse shows a stack backtrace, a list of all the methods called when the exception was thrown. The Variables view shows that activityException now refers to the exception that was thrown. Look at the members of the exception to see the information this exception provides.

If you examine the exception that was thrown (you can do this by hovering your mouse over activityException) you will see that the explanation for the exception reads "No activity found to handle intent." That is, in the case of an Intent object created with Intent.ACTION_CALL as the argument to the constructor, it also needs the data of the Intent to be set correctly in order to find an activity to process that Intent.

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