IOS之UIView的tag學習，iosuiviewtag

IOS之UIView的tag學習，iosuiviewtag

tag是UIView的一個屬性，而且要求tag值唯一。父視圖可以通過tag來找到一個子視圖

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

下面來看下幾種需要注意的錯誤樣本

由於範例程式碼有點多，怕麻煩的童鞋可以跳到最後的結論部分(最好把錯誤樣本4的代碼看一下)

一，view下有tag值相同的兩個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]];錯誤樣本1

結果是yellowView的背景被改變了，說明這種情況下會取得父視圖載入的第一個tag是1000的子視圖。

 

二，父視圖取得子視圖的子視圖。

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]];樣本2

結果是greenView背景被改變了，說明這個是可行的。

 

三，取存在但不是自己子視圖的視圖

將樣本2中的倒數第二句代碼改為   

UIView *getView = [redView viewWithTag:1003];

結果是greenView的背景沒有被改變，說明這是行不通的。

 

四，別的視圖中的子視圖和本視圖的子視圖有相同的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]];錯誤樣本3

結果來看還可以

 

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]];錯誤樣本4

結果是greenView的背景色被改變了。

 

最後說一下結論

由以上的代碼可以推出，父視圖通過tag取得子視圖的順序是深度優先，也就是先查看自己的第一個子視圖，然後查看第一個子視圖的所有子視圖的

tag值，直到第一個子視圖下的所有子視圖搜尋完，再搜尋自己第二個子視圖，直到找到為止。找不到就返回nil。

 

當然，最穩妥的方法還是確保tag值的唯一。