delegate是iOS编程中的一种设计模式，它适用与让一个对象去检测自定义控件的各种状态。

 我们可以用这个设计模式来让单继承的objective-c类表现出它父类之外类的特征.

代码如下： 一个类CustomView继承于NSObject，它加载在MainViewController上。这段代码的主要用途就是几种触摸事件

首先，先定义CustomView，在其头文件中定义代理CustomViewDelegate

 同时声明3个方法

@protocol CustomViewDelegate <NSObject>

 @optional    //可选择性

//开始有关的状态：customView开始被触摸

-(void)customViewBeganTouch:(CustomView *)customView;

// customView 被move

-(void)customViewMoveTouch:(CustomView *)customView;

//customView 触摸结束

-(void)customViewEndedTouch:(CustomView *)customView;

@end

@interface CustomView : UIView

@property (nonatomic, assign) id<CustomViewDelegate> delegate;

@end

然后在CustomView.m中通知delegate执行的某个协议方法

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event

{

     //通知delegate执行的某个协议方法

    if ([_delegate respondsToSelector:@selector(customViewBeganTouch:)]) {

           [_delegatecustomViewBeganTouch:self];

    }

}

-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event

{

     if ([_delegaterespondsToSelector:@selector(customViewMoveTouch:)]) {

        [_delegatecustomViewMoveTouch:self];

    }

}

-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event

{

    if ([_delegaterespondsToSelector:@selector(customViewEndedTouch:)]) {

        [_delegatecustomViewEndedTouch:self];

    }

}

在这个时候，CustomView的事情做完了，可以简单的理解为封装完了，接下来就该处理MainViewController中的问题了

MainViewController只要在定义CustomView的时候指定其代理为自身，就可以执行了

这时候先要在MainViewController.h中导入CustomView的头文件

#import <UIKit/UIKit.h>

#import "CustomView.h"

 @interface MainViewController : UIViewController<CustomViewDelegate>

 @end

剩下的事情就在MainViewController.m中处理了

要先创建customView的对象，设置delegate

- (void)viewDidLoad

{

    [superviewDidLoad];

  //创建customView的对象，设置delegate

    CustomView *customView = [[CustomView alloc]initWithFrame:CGRectMake(50, 50, 50, 50)];

    customView.backgroundColor = [UIColorredColor];

    [self.view addSubview:customView];

    [customView release];

    customView.delegate = self;    // 设置代理（delegate）

}

最后实现功能

-(void)customViewBeganTouch:(CustomView *)customView

{

    self.view.backgroundColor = [UIColorcolorWithRed:arc4random()%256/255.0green:arc4random()%256/255.0blue:arc4random()%256/255.0alpha:1.0];

}

-(void)customViewEndedTouch:(CustomView *)customView

{

    customView.center = CGPointMake(arc4random()%321, arc4random()%481);

}

以上就是简单的代理模式了。