Checking to see if an optional protocol method has been implemented

Question

Does anyone know the best way to check to see if an optional protocol method has been implemented.

I tried this:

if ([self.delegate respondsToSelector:@selector(optionalProtocolMethod:)] )

where delegate is:

id<MyProtocol> delegate;

However, I get an error saying that the function respondsToSelector: is not found in the protocol!

score 101 · Accepted Answer · answered Feb 04 '09 at 18:23

101

respondsToSelector: is part of the NSObject protocol. Including NSObject in MyProtocol should solve your problem:

@protocol MyProtocol <NSObject>

@optional
-(void)optionalProtocolMethod:(id)anObject;

@end

answered Feb 04 '09 at 18:23

Will Harris

3

Except you're not supposed to retain your delegates, so why are you calling [delegate release]? – SilverSideDown Jul 17 '12 at 15:09
1

To be fair to grilix there are situations where a delegate must be retained. – Mike Weller Oct 14 '12 at 18:34
@MikeWeller Curious about use cases for retaining the delegate. Any examples of why you would do this? – memmons Mar 27 '13 at 18:11

score 5 · Answer 2 · answered May 10 '15 at 07:01

5

What I do is applying the following recipe:

if(self.delegate && [self.delegate respondsToSelector:@selector(closed)]){
    [self.delegate closed];
}

Where 'closed' is the method that I wanted to call.

answered May 10 '15 at 07:01

Does that a overkill? If delegate doesn't exist. [self.delegate respondsToSelector:@selector(closed)] will return nil. – Alex Aug 25 '20 at 16:58

2 Answers2