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  • 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

    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

     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

    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

    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

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  • 原文地址:https://www.cnblogs.com/ieso-ios/p/5114416.html
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