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需求是這樣的：一個半透明的背景圖，上面添加不透明的子視圖，在這個子視圖上面再添加一個半透明的試圖。而往往，設(shè)置背景圖的alpha值之后，子視圖也會變得透明。這就需要特殊處理一下。
類似下圖的效果：
實現(xiàn)這種效果，就不能直接通過setAlpha來設(shè)置alpha值。而是要通過colorWithAlphaComponent，如：[[UIColor blackColor] colorWithAlphaComponent:0.5];
效果圖實現(xiàn)的代碼：
- <span style="font-family:KaiTi_GB2312;font-size:18px;"> UIView *view = [[UIView alloc] initWithFrame:CGRectMake(10, 200, 300, 300)];
- view.backgroundColor = [[UIColor redColor] colorWithAlphaComponent:0.5];
- [self.view addSubview:view];
-
- UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(30, 30, 240, 240)];
- imageView.image = [UIImage imageNamed:@"11.jpg"];
- [view addSubview:imageView];
-
- UIView *subView = [[UIView alloc] initWithFrame:CGRectMake(30, 30, 180, 180)];
- subView.backgroundColor = [[UIColor blackColor] colorWithAlphaComponent:0.5];
- [imageView addSubview:subView];</span>
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