ios - Autolayout crash when applying transform: Assertion failure in -[layoutSublayersOfLayer:]

Question

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]];

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

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

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.

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

Anyone that can helps here?

Answer 1

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