委託Delegate是協議的一種，通過一種@protocol的方式實現，顧名思義，就是委託他人幫自己去做什麼事。也就是當自己做什麼事情不方便的時候，就可以建立一個委託，這樣就可以委託他人幫自己去實現什麼方法。
簡單的總結了一下自己用到的委託的作用有兩個，一個是傳值，一個是傳事件。1.所謂傳值經常用在B類要把自己的一個資料或者對象傳給A類，讓A類去展示或者處理。（這個作用在兩個View視圖之間傳遞參數的時候特別有用）（例子一）2.所謂傳事件就是A類發生了什麼事，把這件事告訴關注自己的人，也就是委託的對象，由委託的對象去考慮發生這個事件後應該做出什麼反映。簡單的說，假如A類發生某個事件，它本身並不出來，而是通過委託delegate的形式，讓它的委派物件B類去處理（當然委派物件B就要實現委託中的方法）。（例子二）----下面都會有例子展示。 實現委託的過程中還要注意一些問題： 1、委託過程中需要定義協議@protocol ，這個協議可以單獨New File成一個單獨的協議檔案，也可以放在委派物件的標頭檔中，一般的習慣是後者。 2、在協議中定義委派物件需要委託別人處理的一些方法，用於傳值或者傳事件。 3、委託類中需要定義一個協議的執行個體對象，注意屬性一般設定為assign而非retain（一般命名為delegate，但是注意假如給類中原本就又這個屬性，就要換一個名字），通過這個協議執行個體對象就可以調用協議中的方法（即委託方法）。 4、被委託類中需要在自身的interface中聲明協議：<XXXDelegate>,表示該類要實現XXXDelegate協議中的方法。 5、注意最後要把委託類對象的delegate設定為被委託類對象，一般的處理有兩種方法： ①委託類對象.delegate = 被委託類對象。 ②在被委託類裡定義一個委託類對象，並設定委託類對象.delegate = self （例子三） 下面通過三個例子demo就可以更生動的體會了。 一、通過委託傳值 下面簡要說明一下這個例子： 委託類是：Customer，其中委託協議中定義了一個方法，該方法表示customer要買一個iphone（會傳遞一個iphone型號參數），customer通過委託delegate調用這個方法表示customer要買iphone。 被委託類是：Businessman，其繼承這個協議，實現了協議中的方法，也即處理了委託類customer要買iphone的需要。 下面貼代碼： Customer.h [cpp] #import <Foundation/Foundation.h> @protocol MyDelegate <NSObject> -(void)buyIphone:(NSString*)iphoneType; @end @interface Customer : NSObject @property(nonatomic,assign)id<MyDelegate> delegate; -(void)willBuy; @end #import <Foundation/Foundation.h> @protocol MyDelegate <NSObject> -(void)buyIphone:(NSString*)iphoneType; @end @interface Customer : NSObject @property(nonatomic,assign)id<MyDelegate> delegate; -(void)willBuy; @endCustomer.m [cpp] #import "Customer.h" @implementation Customer @synthesize delegate; -(void)willBuy { [delegate buyIphone:@"Iphone5"]; } @end #import "Customer.h" @implementation Customer @synthesize delegate; -(void)willBuy { [delegate buyIphone:@"Iphone5"];} @endBusinessman.h [cpp] #import <Foundation/Foundation.h> #import "Customer.h" @interface Businessman : NSObject<MyDelegate> @end #import <Foundation/Foundation.h>#import "Customer.h" @interface Businessman : NSObject<MyDelegate> @endBusinessman.m [cpp] #import "Businessman.h" @implementation Businessman -(void)buyIphone:(NSString *)iphoneType { NSLog(@"There is an Iphone store,we have %@",iphoneType); } @end #import "Businessman.h" @implementation Businessman -(void)buyIphone:(NSString *)iphoneType { NSLog(@"There is an Iphone store,we have %@",iphoneType);} @endmain.m [cpp] #import <Foundation/Foundation.h> #import "Customer.h" #import "Businessman.h" int main(int argc, const char * argv[]) { @autoreleasepool { // insert code here... Customer *customer = [[Customer alloc]init]; Businessman *businessman = [[Businessman alloc]init]; customer.delegate = businessman; [customer willBuy]; } return 0; } #import <Foundation/Foundation.h> #import "Customer.h"#import "Businessman.h" int main(int argc, const char * argv[]){ @autoreleasepool { // insert code here... Customer *customer = [[Customer alloc]init]; Businessman *businessman = [[Businessman alloc]init]; customer.delegate = businessman; [customer willBuy]; } return 0;}二、通過委託傳事件 下面也是簡單說一下這個例子： 委託類：Boss 他要處理起草檔案和接電話的任務，但是他本身並不實現這些事件響應的方法，而是通過委託讓他的被委託類來實現這些回應程式法。 被委託類：Secretary 他受Boss的委託實現起草檔案和接電話任務的方法。 下面貼代碼： Boss.h [cpp] #import <Foundation/Foundation.h> @protocol MissionDelegate <NSObject> -(void)draftDocuments; -(void)tellPhone; @end @interface Boss : NSObject @property(nonatomic, assign)id<MissionDelegate> delegate; -(void)manage; @end #import <Foundation/Foundation.h> @protocol MissionDelegate <NSObject> -(void)draftDocuments; -(void)tellPhone; @end @interface Boss : NSObject @property(nonatomic, assign)id<MissionDelegate> delegate; -(void)manage; @endBoss.m [cpp] #import "Boss.h" @implementation Boss @synthesize delegate = _delegate; -(void)manage { [_delegate draftDocuments]; [_delegate tellPhone]; } @end #import "Boss.h" @implementation Boss @synthesize delegate = _delegate; -(void)manage { [_delegate draftDocuments]; [_delegate tellPhone];}@endSecretary.h [cpp]#import <Foundation/Foundation.h> #import "Boss.h" @interface Secretary : NSObject <MissionDelegate> @end #import <Foundation/Foundation.h>#import "Boss.h"@interface Secretary : NSObject <MissionDelegate> @endSecretary.m [cpp] #import "Secretary.h" @implementation Secretary -(void)draftDocuments { NSLog(@"Secretary draft documents"); } -(void)tellPhone { NSLog(@"Secretary tell phone"); } @end #import "Secretary.h" @implementation Secretary -(void)draftDocuments { NSLog(@"Secretary draft documents");} -(void)tellPhone { NSLog(@"Secretary tell phone");} @endmain.m [cpp] #import <Foundation/Foundation.h> #import "Secretary.h" #import "Boss.h" int main(int argc, const char * argv[]) { @autoreleasepool { // insert code here... Boss *boss = [[Boss alloc] init]; Secretary *secretary = [[Secretary alloc] init]; boss.delegate = secretary; [boss manage]; } return 0; } #import <Foundation/Foundation.h>#import "Secretary.h"#import "Boss.h" int main(int argc, const char * argv[]){ @autoreleasepool { // insert code here... Boss *boss = [[Boss alloc] init]; Secretary *secretary = [[Secretary alloc] init]; boss.delegate = secretary; [boss manage]; } return 0;}三、這個例子兩個view視圖之間傳遞參數 定義一個MyView類，在這個視圖中添加了一個button，button的事件響應他本身不處理，而讓被委託類去處理，所以它就是委託類。 在主視圖中，添加一個MyView類的執行個體對象，設定該執行個體對象的代理為self，所以它就是委託類了。 下面還是貼代碼，應該都是很容易看懂的。 MyView.h [cpp] #import <UIKit/UIKit.h> @protocol MyDelegate <NSObject> -(void)print:(NSString*)viewName; @end @interface MyView : UIView @property(nonatomic,assign)id<MyDelegate> mydelegate; @end #import <UIKit/UIKit.h> @protocol MyDelegate <NSObject> -(void)print:(NSString*)viewName; @end @interface MyView : UIView @property(nonatomic,assign)id<MyDelegate> mydelegate; @endMyView.m [cpp] #import "MyView.h" @implementation MyView @synthesize mydelegate = _mydelegate; - (id)initWithFrame:(CGRect)frame { self = [super initWithFrame:frame]; if (self) { //代碼建立一個button UIButton *button = [UIButton buttonWithType:UIButtonTypeRoundedRect]; [button setTitle:@"Button" forState:UIControlStateNormal]; [button setFrame:CGRectMake(10, 10, 100, 50)]; [button setTintColor:[UIColor blueColor]]; //Target-Action模式 為button指定事件處理對象target為self，事件處理方法為buttonPressed [button addTarget:self action:@selector(buttonPressed) forControlEvents:UIControlEventTouchUpInside]; [self addSubview:button]; } return self; } //事件處理的回應程式法 -(void)buttonPressed{ [_mydelegate print:@"this is a view"]; } @end #import "MyView.h" @implementation MyView @synthesize mydelegate = _mydelegate; - (id)initWithFrame:(CGRect)frame{ self = [super initWithFrame:frame]; if (self) { //代碼建立一個button UIButton *button = [UIButton buttonWithType:UIButtonTypeRoundedRect]; [button setTitle:@"Button" forState:UIControlStateNormal]; [button setFrame:CGRectMake(10, 10, 100, 50)]; [button setTintColor:[UIColor blueColor]]; //Target-Action模式 為button指定事件處理對象target為self，事件處理方法為buttonPressed [button addTarget:self action:@selector(buttonPressed) forControlEvents:UIControlEventTouchUpInside]; [self addSubview:button]; } return self;}//事件處理的回應程式法-(void)buttonPressed{ [_mydelegate print:@"this is a view"];} @endDelegateViewController.h [cpp] #import <UIKit/UIKit.h> #import "MyView.h" @interface DelegateViewController : UIViewController<MyDelegate> @end #import <UIKit/UIKit.h>#import "MyView.h" @interface DelegateViewController : UIViewController<MyDelegate> @endDelegateViewController.m [cpp] #import "DelegateViewController.h" @interface DelegateViewController () @end @implementation DelegateViewController - (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil { self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil]; if (self) { // Custom initialization } return self; } - (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view. MyView *myView = [[MyView alloc]initWithFrame:CGRectMake(50, 100, 200, 100)]; [myView setBackgroundColor:[UIColor yellowColor]]; myView.mydelegate = self; [self.view addSubview:myView]; } -(void)print:(NSString *)viewName { NSLog(@"%@",viewName); } - (void)didReceiveMemoryWarning { [super didReceiveMemoryWarning]; // Dispose of any resources that can be recreated. } @end
