ios - 屏蔽 UIView 和自动布局

Question

我有一个 UIView，我想用另一个 UIView 遮盖，在它的中心打一个洞。这是我的 viewDidLoad:

- (void)viewDidLoad {
[super viewDidLoad];
[self.view addSubview:self.viewToMask];
[self.view addSubview:self.theMask];

[self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.viewToMask attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterX multiplier:1.0 constant:0.0]];
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.viewToMask attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterY multiplier:1.0 constant:0.0]];
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"[cyan(200)]" options:0 metrics:nil views:@{@"cyan": self.viewToMask}]];
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:[cyan(200)]" options:0 metrics:nil views:@{@"cyan": self.viewToMask}]];
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.theMask attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self.viewToMask attribute:NSLayoutAttributeCenterX multiplier:1.0 constant:0.0]];
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.theMask attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.viewToMask attribute:NSLayoutAttributeCenterY multiplier:1.0 constant:0.0]];
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"[mask(100)]" options:0 metrics:nil views:@{@"mask": self.theMask}]];
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:[mask(100)]" options:0 metrics:nil views:@{@"mask": self.theMask}]];
}

它给了我我正在寻找的东西，减去掩蔽:

如果我再添加一行:

[self.viewToMask setMaskView:self.theMask];

两个 View 都消失了 --- 小 View (self.theMask) 遮住了整个大 View (self.viewToMask)，即使它只有一半大小。有谁知道这里发生了什么？您不能将 UIView.maskView 与自动布局一起使用吗？

Answer 1

正如 Zev 所解释的，掩码 View 存在于普通 View 层次结构之外，因此不能与自动布局一起使用。我通过将它手动放置在我的 View Controller 的 viewDidLayoutSubviews 中来解决这个问题:

-(void)viewDidLayoutSubviews{
    [super viewDidLayoutSubviews];
    CGRect viewToMaskRect = self.viewToMask.bounds;
    CGRect maskRect = CGRectMake(viewToMaskRect.origin.x + 50.0, viewToMaskRect.origin.y + 50.0, 100.0, 100.0);
    [self.theMask setFrame:maskRect];
    [self.viewToMask setMaskView:self.theMask];
}