- (void)someMethod { if ( [delegate respondsToSelector:@selector(operationShouldProceed)] ) { if ( [delegate operationShouldProceed] ) { // do something appropriate } } }
The documentation says:
The precaution is necessary only for optional methods in a formal protocol or methods of an informal protocol
What does it mean? If I use a formal protocol I can just use [delegate myMethod]
?
Returns a Boolean value that indicates whether the receiver implements or inherits a method that can respond to a specified message.
The root class of most Objective-C class hierarchies, from which subclasses inherit a basic interface to the runtime system and the ability to behave as Objective-C objects.
You use it pretty much just when you think you need to: to check to see if an object implements the method you are about to call. Usually this is done when you have an optional methods or an informal protocol.
I've only ever used respondsToSelector
when I'm writing code that must communicate with a delegate object.
if ([self.delegate respondsToSelector:@selector(engineDidStartRunning:)]) { [self.delegate engineDidStartRunning:self]; }
You sometimes would want to use respondsToSelector
on any method that returns and id
or generic NSObject
where you aren't sure what the class of the returned object is.
Just to add to what @kubi said, another time I use it is when a method was added to a pre-existing class in a newer version of the frameworks, but I still need to be backwards-compatible. For example:
if ([myObject respondsToSelector:@selector(doAwesomeNewThing)]) { [myObject doAwesomeNewThing]; } else { [self doOldWorkaroundHackWithObject:myObject]; }
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With