protocol的简单写法

 //
 //  TouchView.h
 //  LessonUIControlAndSubClass

 #import <UIKit/UIKit.h>

 @class TouchView;
 //1.制定协议，协议名字格式：类名+Delegate
 @protocol TouchViewDelegate <NSObject>

 @optional
 - (void)touchBegan:(TouchView *)touchView;
 - (void)touchMoved:(TouchView *)touchView;
 - (void)touchEnded:(TouchView *)touchView;
 - (void)touchCancelled:(TouchView *)touchView;

 @end

 @interface TouchView : UIView

 //2.写属性，属性名delegate，类型是id,并且要遵守协议<类名Delegate>
 @property (assign, nonatomic) id<TouchViewDelegate> delegate;

 @end

---

 //
 //  TouchView.m
 //  LessonUIControlAndSubClass
 //

 #import "TouchView.h"

 @implementation TouchView

 //3.一旦找到代理，让代理执行事情
 - (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
     //判断delegate是否实现了某方法
     if ([_delegate respondsToSelector:@selector(touchBegan:)]) {
         [_delegate touchBegan:self];
     }
 }

 - (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
     if ([_delegate respondsToSelector:@selector(touchMoved:)]) {
         [_delegate touchMoved:self];
     }
 }

 - (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
     if ([_delegate respondsToSelector:@selector(touchEnded:)]) {
         [_delegate touchEnded:self];
     }
 }

 - (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event {
     if ([_delegate respondsToSelector:@selector(touchCancelled:)]) {
         [_delegate touchCancelled:self];
     }
 }

 @end