Question

In cocoa-touch development…

1. Use AppDelegate for delegate classes
2. Create separate delegate class and locate in new .h/.m for each class need to use delegate
3. Use view controller classes(whenever such exist) to do that job for all
   classes managed by this controller

What would you recommend?

Answer 1

Well it depends. The entire concept for delegate protocols exist so that you can have a lot of flexibility. Sometimes you take the simply default route but sometimes you need to be able to have a lot of different delegate classes.

(1) App delegate — the app delegate should only be used for UIApplicationDelegateProtocol methods or delegates for actual properties of the delegate instance itself. In other words, if the app delegate doesn’t directly deal with an instance e.g. the application object, then the app delegate should serve as the instance’s delegate. Piling up extranous methods in the app delegate will muddle the app and make it snarlingly interconnected and difficult to debug and maintain.

(2) Wholly separate delegate classes are usually used when you have (A) a large number of delegate protocols to implement or (B) you have the same protocol to implement for multiple instances but require a different behavior for each object’s delegate. E.g. you have several UITextFields each of which behave differently. You create as separate delegate class for each so that each text field has it’s own custom implementation of the delegate protocol’s methods.

(3) Using the controller for delegates is the easiest, most logical and most modular way to go in the majority of cases. In many cases such as UI elements the delegate methods need an awareness of other UI elements which the controller can provide.

In sum, never do (1) as a general parking place for any random delegate methods and default to (3) in the majority of cases.