Graphics Programs Reference
In-Depth Information
Now let's introduce an exception in
Whereami
. In
WhereamiViewController.m
,
delete the entire implementation of
doSomethingWeird
:
- (void)doSomethingWeird
{
NSLog(@"Line 1");
NSLog(@"Line 2");
NSLog(@"Line 3");
}
But don't delete the line in
initWithNibName:bundle:
that sends the
doSo-
methingWeird
message.
Now
WhereamiViewController
no longer implements
doSomethingWeird
, so
when it sends this message to
self
, an unrecognized selector exception will be thrown.
Build and run the application.
Immediately after launch, the application will blow up. The debugger will show you
where (look for the green execution indicator), and the console will show you why. Notice
that the stack trace is a bit longer this time, and the method that caused the exception is
not at the top of the stack trace. This will sometimes be the case: your code supplies bad
data (like an unrecognized selector) to a method, and then somewhere within that meth-
od's implementation, the application crashes. To find the source of the error, look for the
methods you implemented in the stack trace. The culprit may not be at the top, but it will
certainly be one of yours.
Also notice that the compiler warned you that the method definition was not found for
doSomethingWeird
(
Figure 4.14
).
Figure 4.14 Unimplemented method warning
This warning means that you declared a method in the header file but did not implement
it. Now remove the declaration of
doSomethingWeird
from
WhereamiViewCon-
troller.h
.
@interface WhereamiViewController : UIViewController <CLLocationManagerDelegate>
