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代理的一般使用场合为：
1.对象B的内部发生一些事，想通知A,比如B通知A改颜色；
2.对象A想监听对象B内部发生了什么事情；
3.对象B想在自己的方法内部调用对象A的某个方法，并且对象B不能对对象A有耦合依赖；（A遵守协议，执行代理方法）
4.对象B想传递数据给对象A;
……………………
以上情况，结果都一样：对象A是对象B的代理（delegete），即B.delegate = A，对象B让对象A作为它的代理，帮它去做事；
一个最简单的列子来说明delegate的简单使用：界面A push 界面B,然后界面B pop 界面A的时候改变界面A的颜色，即界面B返回传值给界面A;
界面A为 AViewController,界面B为 BViewController
AViewController.h
1 #import <UIKit/UIKit.h> 2 #import "BViewController.h" 3 4 @interface AViewController : UIViewController<ChangeColorDelegate> 5 { 6 BViewController *B; 7 } 8 @end
AViewController.m
1 - (void)viewDidLoad 2 { 3 UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom]; 4 button.frame = CGRectMake(140, 100, 60, 30); 5 button.backgroundColor = [UIColor whiteColor]; 6 [button setTitleColor:[UIColor blackColor] forState:UIControlStateNormal]; 7 button.layer.cornerRadius = 8.0; 8 [button setTitle:@"推出B" forState:UIControlStateNormal]; 9 [button addTarget:self 10 action:@selector(buttonClick:) 11 forControlEvents:UIControlEventTouchUpInside]; 12 [self.view addSubview:button]; 13 14 B = [[BViewController alloc] init]; 15 B.delegate = self;//遵守协议 16 } 17 18 - (void)buttonClick:(id)sender 19 { 20 [self.navigationController pushViewController:B animated:YES]; 21 } 22 //协议方法 23 - (void)changeViewBackGroundColor:(UIColor *)color 24 { 25 self.view.backgroundColor = color; 26 }
BViewController.h
1 #import <UIKit/UIKit.h>
2 @protocol ChangeColorDelegate <NSObject> 3 - (void)changeViewBackGroundColor:(UIColor *)color;//协议方法 4 @end
5 @interface BViewController : UIViewController 6 @property (nonatomic,retain)id<ChangeColorDelegate>delegate; 7 @end
BViewController.m
1 - (void)viewDidLoad 2 { 3 [super viewDidLoad]; 4 self.view.backgroundColor = [UIColor redColor]; 5 UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom]; 6 button.frame = CGRectMake(140, 100, 60, 30); 7 button.backgroundColor = [UIColor whiteColor]; 8 button.layer.cornerRadius = 8.0; 9 [button setTitle:@"变色" forState:UIControlStateNormal]; 10 [button setTitleColor:[UIColor blackColor] forState:UIControlStateNormal]; 11 [button addTarget:self action:@selector(buttonClick:) forControlEvents:UIControlEventTouchUpInside]; 12 [self.view addSubview:button]; 13 } 14 - (void)buttonClick:(id)sender 15 { 16 // if ([self.delegate respondsToSelector:@selector(changeViewBackGroundColor:)]) { 17 // [self.delegate changeViewBackGroundColor:[UIColor colorWithRed:arc4random()%255/255.0f green:arc4random()%255/255.0f blue:arc4random()%255/255.0f alpha:1]]; 18 // } 19 //这样写和上面的是一个意思，不需要加判断更直接，但有时候还是需要加判断的 20 [self.delegate changeViewBackGroundColor:[UIColor colorWithRed:arc4random()%255/255.0f green:arc4random()%255/255.0f blue:arc4random()%255/255.0f alpha:1]]; 21 [self.navigationController popViewControllerAnimated:YES]; 22 }
这样就实现了简单的代理传值
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原文地址：http://www.cnblogs.com/yanshiyu25/p/4211540.html
