How to catch unrecognized selector sent to instance exception?

Question

I am getting after some time unrecognized selector sent to instance exception. When i get this i want just skip it and my app should work.

However i don't know how to catch. As this don't catch:

@property(nonatomic,retain) UIButton *button;
    @try{

       if(button.currentBackgroundImage == nil){//rises exception 
    }
    }@catch(NSException *e){
}

How i could handle this ?

Thanks.

Answer 1

The technique I use and see often is: instead of catching the exception, check if the object responds to the selector:

if(![button respondsToSelector:@selector(currentBackgroundImage)] || button.currentBackgroundImage == nil) {
  // do your thing here...
}

Answer 2

If you are getting this exception, it means there is a design flaw, a bug in your code. Patching it by ignoring the exception is not the right thing to do. Try to pin down why you are sending the wrong message to the wrong object instead. Your code will become more robust and maintainable.

Also, sometimes you get this exception when the object originally was of the right type, but is halfway in the process of being deallocated. Watch out!

If you still want to bypass the exception, read Apple's docs where it explains the multi-step process by which messages are bound to method implementations at run time. There is at least two places where you can catch it by overriding NSObject's default behavior.