iOS_Apprentice_2_Checklists学习总结（4）

Delegates in five easy steps
In review, these are the steps for setting up the delegate pattern between two
objects, where object A is the delegate for object B, and object B will send out
the messages:
1. Define a delegate
protocol for object B.
2. Give object B an optional
delegate variable. This variable should be
weak.
3. Make object B send messages to its delegate when something interesting
happens, such as the user pressing the Cancel or Done buttons, or when it
needs a piece of information.
4. Make object A conform to the delegate protocol. It should put the name of
the protocol in its
class line and implement the methods from the protocol.
5. Tell object B that object A is now its delegate.