How to implement multi-level delegate in Objective-C

Question

I have 4 classes (views):
A, B, C and D

Class A calls B, B calls C, and C Calls D:
A > B > C > D

In class D I have implemented a delegate protocol and I want to catch the delegate event in class A.

How can I achieve this?

Answer 1

There are multiple ways how you could achieve this. What's best in your case depends on the situation. Here are some ideas:

1. You could implement the delegate protocol in all of those classes and simply pass it down the line.
2. You could add an ivar to access class D from A and pass it directly (danger of spaghetti code!)
3. If it's possible you could change your implementation, so that you only implement the delegate in A and handle it right there.
4. A last resort could be using NSNotifications (not to be confused with NSUserNotifications in Mountain Lion). In your class A you post a notification to the default notification center and in class D you register to this notification and handle it as you want. Only use this approach though if nothing else works, because this can result in even worse code.