CollectionView won't stop complaining about undefined behaviour - ios

Question

I have a set of 4 different elements that can be shown in a small horizontal collectionView. There will only be one row, and the collectionView and the elements will always be the same height as each other - however, it needs to be dynamic, in case people increase their text size (accessibility larger text).
To make this work, I have a "spacer" label next to the CollectionView, and tell the collectionView to be the same height as the label, and I do the same in all the cells. They all have the same font.
When I try to run it, the CollectionView prints out this:
The behavior of the UICollectionViewFlowLayout is not defined because:
the item height must be less than the height of the UICollectionView
minus the section insets top and bottom values,
minus the content insets top and bottom values.
Please check the values returned by the delegate.
The relevant UICollectionViewFlowLayout instance is <...>,
and it is attached to <..; frame = (0 438.5; 414 29.5);
clipsToBounds = YES; autoresize = RM+BM; gestureRecognizers = <..>;
layer = <CALayer:..>; contentOffset: {0, 0}; contentSize: {32, 29.5};
adjustedContentInset: {0, 0, 0, 0}> collection view layout: <...>.
Make a symbolic breakpoint at UICollectionViewFlowLayoutBreakForInvalidSizes
to catch this in the debugger.
But everything I can find returns 29.5 or less.
collectionView.contentInsetAdjustmentBehavior = .never
flowLayout.estimatedItemSize = UICollectionViewFlowLayout.automaticSize
ContentInset is .zero, sectionInset is 0 for top and bottom, lineSpacing and interItem-spacing is 0, scrollDirection = .horizontal..
I have not overridden any sizeForItem or anything like that, because it should happen automatically, and I shouldn't have to create custom height logic.
I have tried this in each cell:
override func preferredLayoutAttributesFitting(_ layoutAttributes: UICollectionViewLayoutAttributes) -> UICollectionViewLayoutAttributes {
setNeedsLayout()
layoutIfNeeded()
layoutAttributes.frame.size = contentView.systemLayoutSizeFitting(UICollectionViewCell.layoutFittingCompressedSize)
print("Height: ", layoutAttributes.size)
return layoutAttributes
}
But it just prints out 29.5, which should be correct.
It does print it out after the warnings though, so something happens before this.
When I print out the height of the cell directly after its initialization like this:
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let item = items[indexPath.row]
if let someItem = item as? SomeCellViewModel, let cell = self.dequeueReusableCell(withReuseIdentifier: "SomeIdentifier", for: indexPath) as? SomeCell{
cell.bind(with: someItem)
print("height: ", cell.bounds.size.height)
return cell
}else{ ...
it prints out "50.0". And as I understand, that's the default "Item Size", but I've changed all that! In Storyboard/IB/Xib, the "Collection View Flow Layout" was 50x50, but I have changed it to different things (0x0, 1x1, 20x20, tested a lot). Still it prints out 50.0. The xibs for the cells aren't even 50 in their file. If I try to use the systemLayoutSize-thing directly here to set its frame.size, it warns me about an autoresizing constraint that wants to be 0. I assume I shouldn't be doing such logic here anyway, so I nevermind this.
Since the warning says items "must be less than the height minus X minus Y" (not less than or equal to), I tried making the CollectionView a point taller than the spacer-logic, making the CollectionView 30.5 and the cells 29.5, but I still get the warning.
I have tried setting the symbolic breakpoint, but there is nothing of value there..
The thing is - it looks and behaves correct - on iOS 12. It does not work on iOS 11. There might be a separat constraint-issue within the elements that makes it wrong on iOS 11, I'm looking into it. Either way;
Why am I receiving this warning?
Edit: if I implement sizeForItemAt:IndexPath and statically tell it to be
width:100, height: 29.5, there is no warning at all. Everything is good. But I don't want to do that. I shouldn't need to calculate the individual height like this. And I don't really want to deal with prototype-cells either.
This should work.