Question

I have two classes that can act as a delegate of a third class, and both implement a formal protocol made entirely of optional methods. One of the classes implements everything while another only implements a couple methods that i care about. However, at runtime when i have the second class act as the delegate to the third class, and the third class ends up calling one of the unimplemented optional methods on that delegate, i get a runtime error essentially saying “Target does not respond to this message selector.” I thought that objective-c handled this case correctly, and that it would just do nothing if that method wasn’t actually defined on the class. Might there be something i’m missing?

Answer 1

When you call an optional method of your delegate, you need to make sure it responds to the selector before calling it:

if ([delegate respondsToSelector:@selector(optionalMethod)])
    [delegate optionalMethod];