Layout constraints are breaking when aspect ratio on UIImageView is set

[iBolom]

Describe the bug Well i have collection view cell which contains UIImageView which needs to have 16:9 aspect ratio and two labels below UIImageView. UIImageView needs to be 16:9 and labels below could have dynamic height. If i set aspect ratio on UIImageView 16:9 then i get in debug console this warning: Will attempt to recover by breaking constraint <NSLayoutConstraint:0x60000274edf0 UIImageView:0x12a6287c0.height == 50 (active)>

Besides that when i fast scroll collection view to the bottom layout being totally messed up. I tried also to put low priority for this aspect ratio but then i don't get properly layout(i don't see 2 labels below UIImageView) and when i scroll collection view then cells get bigger(too much).

To Reproduce Steps to reproduce the behaviour:

1. Create UICollectionViewCell which inherits MagazineLayoutCollectionViewCell.
2. Create UIImageView and two labels below UIImageView.
3. Set 16:9 aspect ratio on UIImageView.
4. Setup constraints between 2x UILabel and UIImageView vertically.

Expected behavior Don't get breaking layout constraints when set aspect ratio 16:9 on UIImageView and fast scrolling should not mess up layout.

Smartphone (please complete the following information):

• Device/Simulator: Apple TV 4K
• OS: tvOS

[bryankeller]

Since the collection view temporarily needs to set the cell to an estimated height (before it self-sizes), your contained view needs to be able to layout at a different height without constraints breaking.

At Airbnb, we do this by setting the priority of our bottom-most constraint to .defaultLow. For example:

let bottomConstraint = label.bottomAnchor.constraint(equalTo: bottomAnchor)
bottomConstraint.priority = .defaultLow

NSLayoutConstraint.activate([
  // imageView constraints

  label.topAnchor.constraint(equalTo: imageView.bottomAnchor),
  label.leadingAnchor.constraint(equalTo: leadingAnchor),
  label.trailingAnchor.constraint(equalTo: trailingAnchor),

  bottomConstraint,
])