CODEWITHSUNDEEP
iphoneobjective-cdelegatesoption-type
choise
choise

Reputation: 25244

calling optional delegate methods

i created a delegate for a class

@protocol gameDelegate <NSObject>
@optional
-(void)gameStarted;
@required
@end

now in my game object i called this method:

[self.delegate gameStarted];

so now, if i initiate this object anywhere and set the delegate everything works fine until the gameStated gets called, because its not implemented in the main object where the game object is created (because its optional).

i tried some variations of this

if(![self.delegate respondsToSelector: @selector(gameStarted)]) {
    //[self.delegate gameStarted];
}

but this is not working for me. any ideas how to make this "really" optional?

thanks in advance

Upvotes: 12

Views: 8291

Answers (3)

davetw12
davetw12

Reputation: 1841

To accomplish this in swift, I recommend the following:

@objc protocol MyDelegate {

optional func optionalMethod()

}

class MyClass : MyDelegate {

// optionalMethod() does not have to be declared

}

Then to call the optional on your delegate object, simple use if delegate.optionalMethod?(){}

Upvotes: 1

divergio
divergio

Reputation: 2010

Checking if a delegate implements an optional method and then calling it is such a common pattern that I use a preprocessor macro SAFE_CALL that checks respondToSelector: and then calls the method.

The macro is:

#define SAFE_CALL(obj,method) \
([obj respondsToSelector:@selector(method)] ? [obj method] : nil)

and it is used like this:

SAFE_CALL(sourceDelegate, refresh)
// or 
NSString *response = SAFE_CALL(object, responseValue)

Note this version works only with methods with no parameters.

Originally it was implemented as a C function, but that causes warnings with performSelector leaks when using ARC. As a preprocessor macro it works exactly as expected.

Upvotes: 0

Ole Begemann
Ole Begemann

Reputation: 135548

Omit the negation from your if statement:

if ([self.delegate respondsToSelector:@selector(gameStarted)]) {
    ...
}

Upvotes: 18

Related Questions