IOS之UIView的tag学习

tag是UIView的一个属性，而且要求tag值唯一。父视图可以通过tag来找到一个子视图

     UIView *redView = [[UIView alloc]initWithFrame:CGRectMake(, , CGRectGetWidth(self.window.frame), CGRectGetHeight(self.window.frame)/)];
     redView.backgroundColor = [UIColor redColor];
     redView.tag = ;
 [self.window addSubview:redView];

 UIView *getView = [self.window viewWithTag:];

tag用法

下面来看下几种需要注意的错误示例

由于示例代码有点多，怕麻烦的童鞋可以跳到最后的结论部分(最好把错误示例4的代码看一下)

一，view下有tag值相同的两个subview

     UIView *redView = [[UIView alloc]initWithFrame:CGRectMake(, , CGRectGetWidth(self.window.frame), CGRectGetHeight(self.window.frame)/)];
     redView.backgroundColor = [UIColor redColor];
     redView.tag = ;

     UIView *yellowView = [[UIView alloc]initWithFrame:CGRectMake(, CGRectGetHeight(self.window.frame)/, CGRectGetWidth(self.window.frame), CGRectGetHeight(self.window.frame)/)];
     yellowView.backgroundColor = [UIColor yellowColor];
     yellowView.tag = ;

     [self.window addSubview:yellowView];
     [self.window addSubview:redView];

     UIView *getView = [self.window viewWithTag:];
     [getView setBackgroundColor:[UIColor whiteColor]];

错误示例1

结果是yellowView的背景被改变了，说明这种情况下会取得父视图加载的第一个tag是1000的子视图。

二，父视图取得子视图的子视图。

     UIView *redView = [[UIView alloc]initWithFrame:CGRectMake(, , CGRectGetWidth(self.window.frame), CGRectGetHeight(self.window.frame)/)];
     redView.backgroundColor = [UIColor redColor];
     redView.tag = ;

     UIView *yellowView = [[UIView alloc]initWithFrame:CGRectMake(, CGRectGetHeight(self.window.frame)/, CGRectGetWidth(self.window.frame), CGRectGetHeight(self.window.frame)/)];
     yellowView.backgroundColor = [UIColor yellowColor];
     yellowView.tag = ;

     UIView *blueView = [[UIView alloc]initWithFrame:CGRectMake(, , , )];
     blueView.backgroundColor = [UIColor blueColor];
     blueView.tag = ;

     UIView *greenView = [[UIView alloc]initWithFrame:CGRectMake(, , , )];
     greenView.backgroundColor = [UIColor greenColor];
     greenView.tag = ;

     [redView addSubview:blueView];
     [yellowView addSubview:greenView];

     [self.window addSubview:yellowView];
     [self.window addSubview:redView];

     UIView *getView = [self.window viewWithTag:];
     [getView setBackgroundColor:[UIColor whiteColor]];

示例2

结果是greenView背景被改变了，说明这个是可行的。

三，取存在但不是自己子视图的视图

将示例2中的倒数第二句代码改为

UIView *getView = [redView viewWithTag:];

结果是greenView的背景没有被改变，说明这是行不通的。

四，别的视图中的子视图和本视图的子视图有相同的tag值

     UIView *redView = [[UIView alloc]initWithFrame:CGRectMake(, , CGRectGetWidth(self.window.frame), CGRectGetHeight(self.window.frame)/)];
     redView.backgroundColor = [UIColor redColor];
     redView.tag = ;

     UIView *yellowView = [[UIView alloc]initWithFrame:CGRectMake(, CGRectGetHeight(self.window.frame)/, CGRectGetWidth(self.window.frame), CGRectGetHeight(self.window.frame)/)];
     yellowView.backgroundColor = [UIColor yellowColor];
     yellowView.tag = ;

     UIView *blueView = [[UIView alloc]initWithFrame:CGRectMake(, , , )];
     blueView.backgroundColor = [UIColor blueColor];
     blueView.tag = ;

     UIView *greenView = [[UIView alloc]initWithFrame:CGRectMake(, , , )];
     greenView.backgroundColor = [UIColor greenColor];
     greenView.tag = ;

     [redView addSubview:blueView];
     [yellowView addSubview:greenView];

     [self.window addSubview:yellowView];
     [self.window addSubview:redView];

     UIView *getView = [redView viewWithTag:];
     [getView setBackgroundColor:[UIColor whiteColor]];

错误示例3

结果来看还可以

五，greenView和redView的tag值相同

     UIView *redView = [[UIView alloc]initWithFrame:CGRectMake(, , CGRectGetWidth(self.window.frame), CGRectGetHeight(self.window.frame)/)];
     redView.backgroundColor = [UIColor redColor];
     redView.tag = ;

     UIView *yellowView = [[UIView alloc]initWithFrame:CGRectMake(, CGRectGetHeight(self.window.frame)/, CGRectGetWidth(self.window.frame), CGRectGetHeight(self.window.frame)/)];
     yellowView.backgroundColor = [UIColor yellowColor];
     yellowView.tag = ;

     UIView *blueView = [[UIView alloc]initWithFrame:CGRectMake(, , , )];
     blueView.backgroundColor = [UIColor blueColor];
     blueView.tag = ;

     UIView *greenView = [[UIView alloc]initWithFrame:CGRectMake(, , , )];
     greenView.backgroundColor = [UIColor greenColor];
     greenView.tag = ;

     [redView addSubview:blueView];
     [yellowView addSubview:greenView];

     [self.window addSubview:yellowView];
     [self.window addSubview:redView];

     UIView *getView = [self.window viewWithTag:];
     [getView setBackgroundColor:[UIColor whiteColor]];

错误示例4

结果是greenView的背景色被改变了。

最后说一下结论

由以上的代码可以推出，父视图通过tag取得子视图的顺序是深度优先，也就是先查看自己的第一个子视图，然后查看第一个子视图的所有子视图的

tag值，直到第一个子视图下的所有子视图搜索完，再搜索自己第二个子视图，直到找到为止。找不到就返回nil。

当然，最稳妥的方法还是确保tag值的唯一。