objective c - Why use weak pointer for delegation?

Question

I can't understand why it is correct to define a delegate with weak pointer :

@property (nonatomic,weak) id delegate;

I can't realize why isn't necessary to retain a reference to the delegate... i don't want the object that i use as the delegate to be deallocated... thus, i would prefer using a strong reference not a weak!

In many cases the delegate is the same object where the instance of my class will be created, in this case creating a weak reference would be a great solution to avoid retain cycle... but what if I choose a totally different object as the delegate ?

I searched for other questions on stack overflow but I can't find something that can help me to fully understand this situation.

Answer 1

The reason that objects weakly retain their delegates is to avoid retain cycles. Imagine the following scenario: object a creates b and retains it, then sets itself as b's delegate. a is released by its owner, leaving a retain cycle containing a and b. This is actually a very common scenario. Consider a view controller that owns a view and acts as that view's delegate. In this case, the view should not retain the controller—as a mater of proper MVC architecture and to prevent retain cycles.