I'm not sure it is trickery, but it is useful. When a controller becomes a delegate for a view it sure makes things easy and hold together for the MVC pattern.

@interface CategoriesViewController : UIViewController

So, I declare my view controller and add in a few protocols and I'm in business. Well, have access to the "business" anyway. I don't know how this is done in the OO runtime world, where it came from, (Smalltalk?) but I sure do like it.