IOS学习之Delegate设计模式

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 a property for that delegate protocol.

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 @interface line and implement the methods from the protocol.

5. Tell object B that object A is now its delegate. 

tips:

1.if screen A(object A) launches screen B(object B) then you don’t want screen B to know too much about the screen that invoked it (A).

2.Using a delegate helps to abstract the dependency from screen B on screen A. 

3.Anytime you want one part of your app to notify another part about something, usually in order to update the screen, you want to use delegates. 

4.if screen A opens screen B, then A can give B the data it needs. You simply make a property for this data on screen B and then screen A puts something into this property right before it makes screen B visible.To pass data back from B to A you would use a delegate.