Objective C delegates and class methods vs instance methods

Question

There is a similar question to mine on the following link but it doesn't quite answer my query.

I am setting a helper class for Facebook (follows the delegation pattern) . An example of one of the class methods would be:

+ (void)openSession:(id)delegate;

This method calls a the Facebook openActiveSessionWithReadPermissions method which expects a completionHandler block. Would it make sense to call the delegate method, say sessionStateChanged in the block as follows?

[delegate sessionStateChanged];

Or is it better to use instance methods for the Facebook helper class and call the delegate using [self.delegate sessionStateChanged] in the completionHandler block.

Answer 1

I tried both methods i.e. using class and instance methods. Any of them will do, though to follow the proper delegation pattern I believe using instance methods is more appropriate.

Answer 2

You would be better off with a block parameter rather than a delegate as a parameter if it is just for a single callback.

+ (void)openSession:(void (^)(void))sessionStateChangedBlock

That way you don't have to worry about defining a delegate protocol.

If you want to use a delegate, you will have to define a delegate variable at the class level. You can't use [self.delegate sessionStateChanged] because you are saving the delegate as a class variable. self is only available in an instance of the class.