前言：我们知道，当发生点击事件时，系统通过 - (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event查找第一响应者。找到之后触发该响应者的UIResponder中的touch方法。

• 以下分析系统如何实现的，

• 首先我们观察系统的打印结果，在- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event 中添加如下代码

- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event{    NSLog(@"hit start -- >%ld",self.tag);    UIView *v = [super hitTest:point withEvent:event];    NSLog(@"hit end %ld ->%@",self.tag,v);    return v;}复制代码

• 打印结果如下

hit start -- >100 hit start -- >101 hit end 101 ->(null) hit start -- >102 hit start -- >104 hit end 104 ->
    
     > hit end 102 ->
     
      > hit end 100 ->
      
       > hit start -- >100 hit start -- >101 hit end 101 ->(null) hit start -- >102 hit start -- >104 hit end 104 ->
       
        > hit end 102 ->
        
         > hit end 100 ->
         
          > 104 ->-[TestView touchesBegan:withEvent:]复制代码
         
        
       
      
     
    

• 以下是模仿系统实现的方法

- (UIView *)__adHitTest:(CGPoint)point withEvent:(UIEvent *)event{    if (![self pointInside:point withEvent:event]) {        return nil;    }        if (self.userInteractionEnabled == NO) {        return nil;    }        if (self.alpha < 0.01) {        return nil;    }        if (self.hidden == YES) {        return nil;    }        if (self.subviews.count) {                for (NSUInteger i = self.subviews.count; i > 0; i--) {                    UIView *sub = self.subviews[i-1];                        CGPoint p = [self convertPoint:point toView:sub];                        UIView *t = [sub hitTest:p withEvent:event];                        if (t != nil) {                return t;            }        }    }        return self;}复制代码

• 在- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event换成模仿的实现

- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event{    NSLog(@"hit start -- >%ld",self.tag);    UIView *v = [self __adHitTest:point withEvent:event];    NSLog(@"hit end %ld ->%@",self.tag,v);    return v;}复制代码

• 观察模仿后的打印结果

hit start -- >100  hit start -- >101  hit end 101 ->(null)  hit start -- >102  hit start -- >104  hit end 104 ->
    
     >  hit end 102 ->
     
      >  hit end 100 ->
      
       >  hit start -- >100  hit start -- >101  hit end 101 ->(null)  hit start -- >102  hit start -- >104  hit end 104 ->
       
        >  hit end 102 ->
        
         >  hit end 100 ->
         
          > 104 ->-[TestView touchesBegan:withEvent:]复制代码
         
        
       
      
     
    

###是不是差不多？