How do I get rid of the warning <Class> may not respond to <Selector>?

Question

The below code behaves as expected however the compiler keeps telling me this: warning: 'StatusViewController' may not respond to '-beginLoadingThreadData'

How do I get rid of that warning and most important why xcode believes that is the case?

here is my code:

[self beginLoadingThreadData]; // called in the loadDidView block

- (void)beginLoadingThreadData
{
    [NSThread detachNewThreadSelector:@selector(loadThreadData) toTarget:self withObject:nil];
}

- (void)loadThreadData
{
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    [NSThread sleepForTimeInterval:2];
    [self performSelectorOnMainThread:@selector(finishedLoadingThreadData) withObject:nil waitUntilDone:NO];
    [pool release];
}

- (void)finishedLoadingThreadData
{
    [[BusinessLogic instance] startTracking:self];
}

Answer 1

You have to either move the definition of loadingThreadData before the definition of viewDidLoad, or define it in the header file for StatusViewController, for example by inserting -(void)beginLoadingThreadData; before the @end in the header file (probably StatusViewController.h).

The reason is that if you don't do this, when the compiler reached your viewDidLoad method, and sees the call to beginLoadingThreadData, it has not yet seen the definition of beginLoadingThreadData, and hasn't been assured (by seeing a declaration with the method signature in the header file) that such a definition exists. Therefore it warns you that the method you're trying to call might not exist.

Answer 2

Declare that method before you use it. I'm assuming it's a private method, in which case you would add a class extension at the top of the implementation file:

@interface MyClass ()
- (void) beginLoadingThreadData;
@end

If it's a public method, make sure you've declared the method in your header and #imported the header at the top of the implementation file.