Delegation is the Template Method design pattern

[bytor99999]

OK, this is more a statement than a question.

Delegation had been giving me a little problem when trying to create one myself, rather than the common implementing the TableView delegate methods.

So, after reading and examining, this is the Template Method design pattern. So why did they change the name to delegation. Just to confuse those who already know design patterns? Just to be different?

The one thing that is a bit different is in the Template Method pattern your parent class is abstract and you extend it in your subclass, whereas in Apple's delegate world there is no inheritance here. so one class has a reference to another and delegates to it, which takes from the Gang of Four Delegation pattern. But it resembles the Template Method pattern more. The Hollywood Principle, "don't call us, we'll call you"

Mark

[bytor99999]

And the formal version of the delegate pattern here in Apple has you create a protocol which is like an interface/abstract class, then you are basically subclassing.

Mark

[Duncan C]

Originally Posted by bytor99999

OK, this is more a statement than a question.

Delegation had been giving me a little problem when trying to create one myself, rather than the common implementing the TableView delegate methods.

So, after reading and examining, this is the Template Method design pattern. So why did they change the name to delegation. Just to confuse those who already know design patterns? Just to be different?

Sorry, I disagree. delegation is a different design pattern than the Template Method design pattern. In Template Method, you create methods that you then override in your subclasses to fine-tune the behavior of the classes.

Delegation is different. Delegation allows one object (the delegate) to modify the behavior of another object. It is possible to assign different delegates to different instances of an object at runtime, which can cause identical objects with different delegate objects to behave differently.

Delegates are also very useful for things like async operations. You create an object to handle an async process, and assign a delegate that gets notified at key points in the async process.

An object is only aquatinted with it's delegate, but in the template method, the abstract object and its subclass are aggregated.

Apple's delegation design pattern IS the gang of 4 delegation pattern. Why do you say it's closer to the template method pattern?

[bytor99999]

True, I said in my post that it isn't 100% the Gang of Four Template Method patter. But I was reading documentation on Delegation and they said that the formal version has a protocol, which is like an interface or abstract class that your class that implements it is like a subclass.

I have definitely found that objective-c is very different in its OO principle usage. Calling the .h file @interface, when a protocol is actually like an interface.

Anyway, it just seems to me more towards Template Method than Delegate design pattern. I do agree that it isn't exactly the Template Method with true subclasses implementing the difference, and that any class can be a delegate of another. But like subclassing, you can only have one. meaning I can only assign one object as the delegate to another object.

Mark