Question

I have this code:

if([annotation respondsToSelector:@selector(tag)]){
    disclosureButton.tag = [annotation tag];
}

and I get the warning:

‘-tag’ not found in protocol

Fair enough, but I’ve created a new object with the protocol that has a synthesized int tag variable.

EDIT: found why the app was crashing – not this line. Now I just get a warning and the app works fine.

Thanks
Tom

Answer 1

The warning is generated because for the static type of annotation, MKAnnotation, there is no method -tag. As you already checked wether the dynamic type responds to the selector you can ignore the warning in this case.

To get rid of the warning:

• If you expect a certain class you can test for it instead:

  if ([annotation isKindOfClass:[TCPlaceMark class]]) {
      disclosureButton.tag = [(TCPlaceMark *)annotation tag];
  }
  

• For a protocol:

  if ([annotation conformsToProtocol:@protocol(PlaceProtocol)]) {
      disclosureButton.tag = [(id<PlaceProtocol>)annotation tag];
  }
  

• Or if both do not apply use a specific protocol to suppress the warning (useful e.g. with rapidly changing Apple APIs):

  @protocol TaggedProtocol
  - (int)tag;
  @end
  
  // ...
  if([annotation respondsToSelector:@selector(tag)]){
      disclosureButton.tag = [(id<TaggedProtocol>)annotation tag];
  }