Agents and protocols in iOS (delegate)

Source Address: http://download.csdn.net/download/swanzhu/9016861

I. Understanding of agreements and agents

Agreement

Format of the protocol:@protocol Keyword: statement of the agreement

For example

@protocol customalertviewdelegate <NSObject>

methods of <methods> protocols

@optional

The method declared under this keyword is an optional implementation.

@required

// This keyword declares a method that must implement the method, if not implemented, the compilation will report a warning and the program runs crashing.

// If the method is not specified as optional or must be implemented, the default is @required.

@end

Two agents

Agent is an abstract concept, if I want to do one thing, and I do not want to do, can let others help me to do, then others is my agent.

For example, I want to rent a house, I am more lazy, so I think the intermediary plus 50 dollars of fees can help me to find the house, I then to the intermediary call, commissioned intermediary to find a house, at this time intermediary is my agent, I commissioned him to help me find room.

In this case, the intermediary is the agent, the 50-dollar fee is the agreement.

1. first declare the protocol: Create the Protocol file

// Agreement statement

       @protocol changecolordelegate <NSObject>

Method

     -(void) ChangeColor;

(2) then (A) It is necessary to appoint who (principal) to execute the agreement.

Declare an attribute b*delegate in A.h ; Represents who the delegate (agent) is ( the object of Class B ).

id< Agreement > delegate; The principal can be any object that implements the Protocol class

// Statement

@protocol changecolordelegate;

Specifies the proxy object ,

@property (nonatomic,assign) id<changecolordelegate>delegate;

(3) Principal B(agent) is required to comply with the agreement and to complete the prescribed content in accordance with the agreement.

1.B First to implement the Protocol: in the B.h through the < Protocol name > Implementation protocol.

// implement the protocol, don't forget to import the header file at this time

@interface zyfirstviewcontroller:uiviewcontroller<changecolordelegate>

2. the agent needs to be set in B.M : a.delegate = self. (self refers to the object of class B)

Specify proxy

second.delegate=self;

3. Implement the Protocol method.

// Implement protocol method

-(void) changecolor{    self.view.backgroundcolor=[uicolor colorwithred:arc4random ()%256/255.0 green:arc4random ( )%256/255.0 blue:arc4random ()%256/255.0 alpha:1.0];        [Self.navigationcontroller Popviewcontrolleranimated:yes];}

4. Specify under what circumstances the agent executes the protocol method.

// Specify under what conditions to execute

    [_delegate ChangeColor];

The basic idea of three-agent design mode: Two objects work together to solve the problem, through the agent to achieve the communication between object and object.

Essence: Invokes the method by passing the object.

Note: The protocol itself is not a class, there is no parent class and cannot define an instance variable, only the declaration of the method, not the implementation of the method;

Protocols are used to specifically declare methods implemented by other classes, and the methods are more flexible.

Copyright NOTICE: This article for Bo Master original article, without Bo Master permission not reproduced.

Agents and protocols in iOS (delegate)