Cast an instance of a class to a @protocol in Objective-C

Ford_74530 0
Viewed 37024

I have an object (a UIViewController) which may or may not conform to a protocol I've defined.

I know I can determine if the object conforms to the protocol, then safely call the method:

if([self.myViewController conformsToProtocol:@protocol(MyProtocol)]) {
    [self.myViewController protocolMethod]; // <-- warning here
}

However, XCode shows a warning:

warning 'UIViewController' may not respond to '-protocolMethod'

What's the right way to prevent this warning? I can't seem to cast self.myViewController as a MyProtocol class.

objective-c protocols
2 Answers

You can cast it like this:

if([self.myViewController conformsToProtocol:@protocol(MyProtocol)])
{
    id<MyProtocol> p = (id<MyProtocol>)self.myViewController;
    [p protocolMethod];
}

This threw me for a bit, too. In Objective-C, the protocol isn't the type itself, so you need to specify id (or some other type, such as NSObject) along with the protocol that you want.

user_38570
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