Protocol (PROTOCOL) and principal agent (Delegate)

Protocol (Protocol) 's role:

1. Specification interface, used to define a common set of interfaces;

2. Constrain or filter the object.

Agent (Delegate):

It is in itself a design pattern that delegates an object < follows the protocol > does something to reduce the coupling between objects, or to reverse the value.

I. Define a common set of interfaces

1 /** Agreement*/2@protocol Executeprotocol <NSObject>3 4 @required5 /**6 * @brief A method that must be implemented7  */8-(Nsuinteger) qualified;9 Ten  One @optional A /** - * @brief Optional method -  */ the- (void) dosomething; -  -@end

Protocol only. h files, no. m files. Because Protocol only defines a common set of interfaces, it does not provide a concrete implementation method. (A specific implementation requires a class that adheres to the protocol, and then the class can do things as a filtered object, which is discussed later)

If the controller needs to use the protocol, then the import protocol:

1 #import "ExecuteProtocol.h"

and implement the required method of the Protocol (otherwise the compiler will warning)

The code for Viewcontroller is as follows:

1 #import "ViewController.h"2 #import "ExecuteProtocol.h"3 #import "Object.h"4 5 @interfaceViewcontroller ()6@property (nonatomic, strong) UILabel *label;7 @end8 9 @implementationViewcontrollerTen  One #pragmaMark-view lifeCycle A- (void) Viewdidload { - [Super Viewdidload]; - [Self.view AddSubview:self.label]; the [self Gethouse:[[object alloc] init]]; - } -  -- (void) Gethouse: (ID<ExecuteProtocol>) obj { +Self.label.text = [NSString stringWithFormat:@"%lu", [obj qualified]]; - } +  A #pragmaMark-getter Methods at-(UILabel *) Label { -     if(!_label) { -_label = [[UILabel alloc] Initwithframe:cgrectmake ( -, -, -, -)]; -_label.textalignment =Nstextalignmentcenter; -_label.backgroundcolor =[Uicolor Redcolor]; -     } in     return_label; - } to @end

To add a method to the controller, the parameter of this method must be an object that adheres to the protocol, so the object is created:

1 #import <Foundation/Foundation.h>2#import"ExecuteProtocol.h " 3 4 /*  */5@interface object:nsobject <ExecuteProtocol>6 7 @end

and implement the Protocol method:

1 #import " Object.h " 2 3 @implementation Object 4 5 - (Nsuinteger) qualified {6     return; 7 }89@end

Simple small Demo.

Second, the agent value (Secondaryviewcontroller value to Viewcontroller)

1. In the Viewcontroller

1 // Viewcontroller need to comply with the agent 2 @interface Viewcontroller () <SecondaryViewControllerDelegate>34  Secondaryviewcontroller *SECVC = [[Secondaryviewcontroller alloc] init]; 5  // Specify proxy 6  SECVC. delegate = self ; 7  [Self.navigationcontroller PUSHVIEWCONTROLLER:SECVC Animated:yes];

1 // implement required Proxy method, realize the value of the transfer, print the result 2 #pragma mark-secondaryviewcontrollerdelegate Methods3 -(void) Controller: ( Secondaryviewcontroller *) Controller text: (NSString *) text {4     NSLog (@ "%@%@  ", Controller, text); 5 }

2. In the Secondaryviewcontroller

1) First, declare the agent

1 #import<UIKit/UIKit.h>2 @classSecondaryviewcontroller;3 4 /**5 * @brief Protocol method (class name +delegate)6  */7 @protocolSecondaryviewcontrollerdelegate <NSObject>8 @required9 /**Ten * @brief Pass value One  * A * @param controllers Current Controller - * @param text value -  */ the- (voidController: (Secondaryviewcontroller *) controller text: (NSString *) text; - @end -  - @interfaceSecondaryviewcontroller:uiviewcontroller + /** - * @brief Agent modified with weak (to prevent memory leaks) +  */ A@property (nonatomic, weak)ID<SecondaryViewControllerDelegate>Delegate; at @end

2) Determine if the agent exists or not and whether the method responds

1 /** 2 * Secondaryviewcontroller3  */4- (void) Touchesbegan: (Nsset<uitouch *> *) touches withevent: (Uievent *)Event {5     /**6 * @brief Determine if the agent is set and the agent responds to the proxy method7      */8     if(self.)Delegate&& [Self.Delegaterespondstoselector: @selector (controller:text:)]) {9[Self.DelegateController:self text:@"Pass Value"];Ten     } One [Self.navigationcontroller Popviewcontrolleranimated:yes]; A}

respecting the author's labor achievements, reprint please specify: "Kingdev"

Protocol (PROTOCOL) and principal agent (Delegate)