委托Delegate是協議的一種，通過一種@protocol的方式實現，顧名思義，就是委托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，就可以建立一個委托，這樣就可以委托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托的作用有兩個，一個是傳值，一個是傳事件。
1.所謂傳值經常用在B類要把自己的一個數據或者對象傳給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，也就是委托的對象，由委托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，而是通過委托delegate的形式，讓它的委托對象B類去處理（當然委托對象B就要實現委托中的方法）。（例子二）
----下面都會有例子展示。
實現委托的過程中還要注意一些問題：
1、委托過程中需要定義協議@protocol ，這個協議可以單獨New
File成一個單獨的協議文件，也可以放在委托對象的頭文件中，一般的習慣是後者。
2、在協議中定義委托對象需要委托別人處理的一些方法，用於傳值或者傳事件。
3、委托類中需要定義一個協議的實例對象，注意屬性一般設置為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），通過這個協議實例對象就可以調用協議中的方法（即委托方法）。
4、被委托類中需要在自身的interface中聲明協議：<XXXDelegate>,表示該類要實現XXXDelegate協議中的方法。
5、注意最後要把委托類對象的delegate設置為被委托類對象，一般的處理有兩種方法：
①委托類對象.delegate
= 被委托類對象。
②在被委托類裡定義一個委托類對象，並設置委托類對象.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、通過委托傳值
下面簡要說明一下這個例子：
委托類是：Customer，其中委托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通過委托delegate調用這個方法表示customer要買iphone。
被委托類是：Businessman，其繼承這個協議，實現了協議中的方法，也即處理了委托類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;
@end
Customer.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"];
}
@end
Businessman.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>
@end
Businessman.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);
}
@end
main.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、通過委托傳事件
下面也是簡單說一下這個例子：
委托類：Boss
他要處理起草文件和接電話的任務，但是他本身並不實現這些事件響應的方法，而是通過委托讓他的被委托類來實現這些響應方法。
被委托類：Secretary
他受Boss的委托實現起草文件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;
@end
Boss.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];
}
@end
Secretary.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>
@end
Secretary.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");
}
@end
main.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，而讓被委托類去處理，所以它就是委托類。
在主視圖中，添加一個MyView類的實例對象，設置該實例對象的代理為self，所以它就是委托類了。
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;
@end
MyView.m
[cpp]
#import "MyView.h"
@implementation MyView
@synthesize mydelegate = _mydelegate;
- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
//代碼創建一個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;
}
//事件處理的響應方法
-(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) {
//代碼創建一個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;
}
//事件處理的響應方法
-(void)buttonPressed{
[_mydelegate print:@"this is a view"];
}
@end
DelegateViewController.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>
@end
DelegateViewController.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
