应用变换时自动布局崩溃:-[layoutSublayersOfLayer:] 中的断言失败

问题描述

我有一个在右下角显示 UILabel 的自定义视图.视图是在从 initWithCoder: 和 initWithFrame: 调用的方法中设置的，如下所示:

I have a custom view that display a UILabel in the bottom right corner. The view is setup in a method called from both initWithCoder: and initWithFrame: like this:

MCLabel* likesLabel = [[MCLabel alloc] init];
likesLabel.mc_textPadding = UIEdgeInsetsMake(0, 10, 0, 10);
likesLabel.font = [UIFont fontWithName:@"FontAwesome" size:12.f];
[likesLabel setText:@"test"];
likesLabel.numberOfLines = 2;
likesLabel.backgroundColor = [UIColor colorWithWhite:1 alpha:.8];
likesLabel.textColor = UIColor.blackColor;
likesLabel.translatesAutoresizingMaskIntoConstraints = NO;
likesLabel.textAlignment = NSTextAlignmentCenter;
likesLabel.mc_verticalTextAlignment = MCVerticalTextAlignmentTop;

[self addSubview:likesLabel];
self.likesLabel = likesLabel;

NSLayoutConstraint* widthConstraint = [NSLayoutConstraint constraintWithItem:likesLabel attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:self attribute:NSLayoutAttributeWidth multiplier:1 constant:1];
NSLayoutConstraint* heightConstraint = [NSLayoutConstraint constraintWithItem:likesLabel attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:likesLabel attribute:NSLayoutAttributeWidth multiplier:2/5.f constant:1];
NSLayoutConstraint* horizontalPosition  = [NSLayoutConstraint constraintWithItem:likesLabel attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self attribute:NSLayoutAttributeRight multiplier:1 constant:1];
NSLayoutConstraint* verticalPosition  = [NSLayoutConstraint constraintWithItem:likesLabel attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self attribute:NSLayoutAttributeBottom multiplier:1 constant:1];
[likesLabel addConstraints:@[heightConstraint]];
[self addConstraints:@[widthConstraint, horizontalPosition, verticalPosition]];

现在，如果我像这样留下所有内容，我不会有任何问题，但是，只要我对此标签应用变换(这是 UILabel 的子类，如果重要，只需添加垂直对齐和边缘插入)应用程序因控制台中的错误而崩溃:

Now if I leave everything like this I do not have any kind of problem but, as soon as I apply a transform to this label (that is a subclass of UILabel that simply add vertical alignment and edge insets if that matters) the app crashes with the error in console:

*** Assertion failure in -[MCView layoutSublayersOfLayer:], /SourceCache/UIKit/UIKit-2935.138/UIView.m:8794
Auto Layout still required after executing -layoutSubviews

断言提示可能子类在覆盖方法时没有调用 [super layoutSubviews] 但我确实调用了.

The assertion hints that probably the subclass didn't call [super layoutSubviews] when overriding the methods but I did.

由于很明显这里的问题是自动布局设置，我担心我忽略了一些东西，也许布局不明确，因此崩溃.

Since is clear that the problem here is the autolayout setup I'm afraid that I'm overlooking at something and maybe the layout is ambiguous hence the crash.

另一个注意事项:如果我在 - (void)didMoveToSuperview 方法中移动转换，相同的代码不会在 iOS 8 上崩溃.

One more note: the same code does not crash on iOS 8 if I move the transform in the - (void)didMoveToSuperview method.

有谁可以帮忙吗?

推荐答案

我在 iOS7(但不是 iOS8)中遇到了这个问题，原因是在 viewWillLayoutSubviews 中进行了约束调整.将约束调整移动到 viewWillAppear 为我修复了它.

I had this issue in iOS7 (but not iOS8) from putting constraint adjustments in viewWillLayoutSubviews. Moving constraint adjustment to viewWillAppear fixed it for me.

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