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I've defined my flow layout as follows

internal lazy var layout: UICollectionViewFlowLayout = {
    let layout = UICollectionViewFlowLayout()
    layout.minimumLineSpacing = 16
    layout.sectionInset = UIEdgeInsets(top: layout.minimumLineSpacing, left: layout.minimumLineSpacing , bottom: layout.minimumLineSpacing , right: layout.minimumLineSpacing )
    layout.estimatedItemSize = CGSize(width: UIScreen.main.bounds.size.width - (layout.sectionInset.left + layout.sectionInset.right), height: 10)
    return layout
}()

In the cell then I set the height for the expected content

override open func preferredLayoutAttributesFitting(_ layoutAttributes: UICollectionViewLayoutAttributes) -> UICollectionViewLayoutAttributes {
    setNeedsLayout()
    layoutIfNeeded()
    let size = contentView.systemLayoutSizeFitting(layoutAttributes.size)
    var newFrame = layoutAttributes.frame
    newFrame.size.height = ceil(size.height)
    layoutAttributes.frame = newFrame
    return layoutAttributes
}

And it works. I get the cells in the height that I expect them to be, but there is a nasty warning in the console coming up for each cell

[LayoutConstraints] Unable to simultaneously satisfy constraints.
    Probably at least one of the constraints in the following list is one you don't want. 
    Try this: 
        (1) look at each constraint and try to figure out which you don't expect; 
        (2) find the code that added the unwanted constraint or constraints and fix it. 
(
    "<NSLayoutConstraint:0x600003c1e490 V:|-(0)-[UIView:0x7fdc8bead5d0]   (active, names: '|':VLCContentCollectionViewCell:0x7fdc8becf8e0 )>",
    "<NSLayoutConstraint:0x600003c1ec60 V:[UIView:0x7fdc8bead5d0]-(0)-|   (active, names: '|':VLCContentCollectionViewCell:0x7fdc8becf8e0 )>",
    "<NSLayoutConstraint:0x600003c4bb60 V:|-(0)-[VLAsyncImageView:0x7fdc8bea20a0]   (active, names: '|':UIView:0x7fdc8bead5d0 )>",
    "<NSLayoutConstraint:0x600003c43070 V:[VLAsyncImageView:0x7fdc8bea20a0]-(0)-|   (active, names: '|':UIView:0x7fdc8bead5d0 )>",
    "<NSLayoutConstraint:0x600003c5f340 VLAsyncImageView:0x7fdc8bea20a0.height == 100   (active)>",
    "<NSLayoutConstraint:0x600003f8cb90 'UIView-Encapsulated-Layout-Height' VLCContentCollectionViewCell:0x7fdc8becf8e0.height == 10   (active)>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x600003c5f340 VLAsyncImageView:0x7fdc8bea20a0.height == 100   (active)>

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKitCore/UIView.h> may also be helpful.

Im pretty sure that it is because of this constraint 'UIView-Encapsulated-Layout-Height' which holds the value for the expected item size of the flow layout, because if I set that to 100 the log message doesn't show up. However, I'm looking for dynamic cell height, so even if I set it to 100 it will fail at other places.

So my question is if I'm doing something wrong in defining my dynamic cells? Or is there maybe a way to reduce the priority of the estimated cell height, so that it will brake that constraint in case?

Hons
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  • [Does this help for your problem ? It seems that someone has the same problem before.](https://stackoverflow.com/q/28161839/419348) – AechoLiu Dec 14 '18 at 08:29
  • 1
    A tech is to lower the priority for some constraints. When conflict happened, autolayout will remove constraint with the lower priority. Is `VLAsyncImageView`'s height fixed with 100 ? How about lower it's height constraint priority ? – AechoLiu Dec 14 '18 at 08:32
  • Or, set `VLAsyncImageView:0x7fdc8bea20a0.height >= 100` ? Let it's min height be 100. – AechoLiu Dec 14 '18 at 08:37

0 Answers0