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[操作系统]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

1   UIView *redView = [[UIView alloc]initWithFrame:CGRectMake(0, 0, CGRectGetWidth(self.window.frame), CGRectGetHeight(self.window.frame)/2)];2   redView.backgroundColor = [UIColor redColor];3   redView.tag = 1000;4 [self.window addSubview:redView];5 6 UIView *getView = [self.window viewWithTag:1000];

tag用法

下面来看下几种需要注意的错误示例

一,view下有tag值相同的两个subview

 1   UIView *redView = [[UIView alloc]initWithFrame:CGRectMake(0, 0, CGRectGetWidth(self.window.frame), CGRectGetHeight(self.window.frame)/2)]; 2   redView.backgroundColor = [UIColor redColor]; 3   redView.tag = 1000; 4    5   UIView *yellowView = [[UIView alloc]initWithFrame:CGRectMake(0, CGRectGetHeight(self.window.frame)/2, CGRectGetWidth(self.window.frame), CGRectGetHeight(self.window.frame)/2)]; 6   yellowView.backgroundColor = [UIColor yellowColor]; 7   yellowView.tag = 1000; 8  9   [self.window addSubview:yellowView];10   [self.window addSubview:redView];11   12   UIView *getView = [self.window viewWithTag:1000];13   [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。

 1   UIView *redView = [[UIView alloc]initWithFrame:CGRectMake(0, 0, CGRectGetWidth(self.window.frame), CGRectGetHeight(self.window.frame)/2)]; 2   redView.backgroundColor = [UIColor redColor]; 3   redView.tag = 1000; 4    5   UIView *yellowView = [[UIView alloc]initWithFrame:CGRectMake(0, CGRectGetHeight(self.window.frame)/2, CGRectGetWidth(self.window.frame), CGRectGetHeight(self.window.frame)/2)]; 6   yellowView.backgroundColor = [UIColor yellowColor]; 7   yellowView.tag = 1001; 8    9   UIView *blueView = [[UIView alloc]initWithFrame:CGRectMake(0, 0, 100, 100)];10   blueView.backgroundColor = [UIColor blueColor];11   blueView.tag = 1002;12   13   UIView *greenView = [[UIView alloc]initWithFrame:CGRectMake(0, 0, 100, 100)];14   greenView.backgroundColor = [UIColor greenColor];15   greenView.tag = 1003;16   17   [redView addSubview:blueView];18   [yellowView addSubview:greenView];19   20   21   [self.window addSubview:yellowView];22   [self.window addSubview:redView];23   24   UIView *getView = [self.window viewWithTag:1003];25   [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:1003];

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

 1   UIView *redView = [[UIView alloc]initWithFrame:CGRectMake(0, 0, CGRectGetWidth(self.window.frame), CGRectGetHeight(self.window.frame)/2)]; 2   redView.backgroundColor = [UIColor redColor]; 3   redView.tag = 1000; 4    5   UIView *yellowView = [[UIView alloc]initWithFrame:CGRectMake(0, CGRectGetHeight(self.window.frame)/2, CGRectGetWidth(self.window.frame), CGRectGetHeight(self.window.frame)/2)]; 6   yellowView.backgroundColor = [UIColor yellowColor]; 7   yellowView.tag = 1001; 8    9   UIView *blueView = [[UIView alloc]initWithFrame:CGRectMake(0, 0, 100, 100)];10   blueView.backgroundColor = [UIColor blueColor];11   blueView.tag = 1002;12   13   UIView *greenView = [[UIView alloc]initWithFrame:CGRectMake(0, 0, 100, 100)];14   greenView.backgroundColor = [UIColor greenColor];15   greenView.tag = 1002;16   17   [redView addSubview:blueView];18   [yellowView addSubview:greenView];19   20   21   [self.window addSubview:yellowView];22   [self.window addSubview:redView];23   24   UIView *getView = [redView viewWithTag:1002];25   [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

 1   UIView *redView = [[UIView alloc]initWithFrame:CGRectMake(0, 0, CGRectGetWidth(self.window.frame), CGRectGetHeight(self.window.frame)/2)]; 2   redView.backgroundColor = [UIColor redColor]; 3   redView.tag = 1000; 4    5   UIView *yellowView = [[UIView alloc]initWithFrame:CGRectMake(0, CGRectGetHeight(self.window.frame)/2, CGRectGetWidth(self.window.frame), CGRectGetHeight(self.window.frame)/2)]; 6   yellowView.backgroundColor = [UIColor yellowColor]; 7   yellowView.tag = 1001; 8    9   UIView *blueView = [[UIView alloc]initWithFrame:CGRectMake(0, 0, 100, 100)];10   blueView.backgroundColor = [UIColor blueColor];11   blueView.tag = 1002;12   13   UIView *greenView = [[UIView alloc]initWithFrame:CGRectMake(0, 0, 100, 100)];14   greenView.backgroundColor = [UIColor greenColor];15   greenView.tag = 1000;16   17   [redView addSubview:blueView];18   [yellowView addSubview:greenView];19   20   21   [self.window addSubview:yellowView];22   [self.window addSubview:redView];23   24   UIView *getView = [self.window viewWithTag:1000];25   [getView setBackgroundColor:[UIColor whiteColor]];

错误示例4

结果是greenView的背景色被改变了

 

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

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