What is the purpose of an iOS delegate?

Question

I understand what a delegate does in iOS, and I\'ve looked at sample code, but I\'m just wondering about the advantages of this type of encapsulation (as opposed to includin

Answer 1

The main advantage of delegation over simply implementing methods in the "primary object" (by which I assume you mean the object doing the delegating) is that delegation takes advantage of dynamic binding. At compile time, the class of the delegate object does not need to be known. For example, you might have a class that delegates the windowDidMove: method. In this class, you'd probably see some bit of code like

if([[self delegate] respondsToSelector:@selector(windowDidMove:)]) {
    [[self delegate] windowDidMove:notification];
}

Here, the delegating class is checking at runtime whether its delegate responds to the given method selector. This illustrates a powerful concept: the delegating class doesn't need to know anything about the delegate other than whether it responds to certain methods. This is a powerful form of encapsulation, and it is arguably more flexible than the superclass-subclass relationship, since the delegator and the delegate are so loosely coupled. It is also preferable to simply implementing methods in the "primary object" (delegating object), since it allows runtime alteration of the method's implementation. It's also arguable that this dynamic runtime makes code inherently more dangerous.