Proxy and Protocol (delegate) in ios)

Proxy and Protocol (delegate) in ios)

 

 

1. Understand protocols and Proxies

 

Protocol

 

Protocol format: @ protocol Keyword: protocol Declaration

 

For example

@protocol CustomAlertViewDelegate 
 

Protocol Method

 

@ Optional

// The method declared under this keyword is an optional method.

 

@ Required

// The method declared by this keyword is a required method. If this method is not implemented, a warning will be reported during compilation and the program running will crash.

 

// If no method is specified, it is optional or required. The default value is @ required.

 

@ End

Proxy 2

 

Proxy is an abstract concept. If I want to do something, but I don't want to do it myself, I can ask someone to help me, then others will be my proxy.

 

For example, if I want to rent a house, I am relatively lazy, so I think that the intermediary can help me find the house by adding 50 yuan of service fees, so I called the intermediary, entrust an intermediary to find a house. At this time, the intermediary is my proxy. I entrust him to help me find a house.

In this example, the intermediary is the proxy, and the handling fee of 50 RMB is the agreement.

 

 

 

1. Declare the Protocol first: Create a Protocol File

// Protocol statement

 

       @protocol ChangeColorDelegate 
 

 

// Method

 

     -(void)changeColor;

 

 

 

(2) then (A) specifies who (principal) is allowed to execute the protocol.

In A. h, declare A property B * delegate, which represents the principal (proxy) who is the object of Class B ).

Id <protocol> delegate; the principal can be any object that implements the Protocol class.

// Statement

 

@protocol ChangeColorDelegate;

 

 

// Specify the proxy object ,,

 

 @property(nonatomic,assign)id
 
  delegate;
 

 

(3) The principal B (agent) must abide by the agreement and complete the provisions in accordance with the Agreement.

1. B First implements the Protocol: in B. h, the Protocol is implemented through the <protocol name>.

// Implement the Protocol. Do not forget to import the header file.

 

@interface ZYFirstViewController : UIViewController
 

 

2. You need to set proxy in B. m: a. delegate = self. (self refers to the object of Class B)

// Specify the proxy

 

second.delegate=self;

 

 

3. implement the Protocol.

// Implementation 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 the circumstances under which the proxy executes the Protocol method.

 

 

// Specify the conditions for execution

 

 

    [_delegate changeColor];

 

 

 

 

 

 

 

 

The basic idea of the Three-agent design mode: two objects work together to solve the problem and implement communication between objects through proxies.

Essence: Call methods by passing objects.

 

 

Note: The Protocol itself is not a class. There is no parent class and instance variables cannot be defined. It only declares the method and does not implement the method;

The protocol is used to specifically declare methods implemented by other classes, and the method functions are more flexible.