UICollectionViewFlowLayout estimatedItemSize does not work properly with iOS12 though it works fine with iOS 11.*

Question

For UICollectionView's dynamic height cells we use,

if let layout = self.collectionViewLayout as? UICollectionViewFlowLayout {     layout.estimatedItemSize = UICollectionViewFlowLayoutAutomaticSize } 

with the proper constraint of height and width, it works fine with iOS 11.* versions but it breaks and does not make the cells dynamic for iOS 12.0

Answer 1

In my case, I solved this by explicitly adding the following constraints to the cell's contentView.

class Cell: UICollectionViewCell {     // ...      override func awakeFromNib() {         super.awakeFromNib()          // Addresses a separate issue and prevent auto layout warnings due to the temporary width constraint in the xib.         contentView.translatesAutoresizingMaskIntoConstraints = false          // Code below is needed to make the self-sizing cell work when building for iOS 12 from Xcode 10.0:         let leftConstraint = contentView.leftAnchor.constraint(equalTo: leftAnchor)         let rightConstraint = contentView.rightAnchor.constraint(equalTo: rightAnchor)         let topConstraint = contentView.topAnchor.constraint(equalTo: topAnchor)         let bottomConstraint = contentView.bottomAnchor.constraint(equalTo: bottomAnchor)         NSLayoutConstraint.activate([leftConstraint, rightConstraint, topConstraint, bottomConstraint])     } } 

These constraints are already in place inside the xib of the cell, but somehow they aren't enough for iOS 12.

The other threads that suggested calling collectionView.collectionViewLayout.invalidateLayout() in various places didn't help in my situation.

Sample code here: https://github.com/larrylegend/CollectionViewAutoSizingTest

This applies the workaround to code from a tutorial by https://medium.com/@wasinwiwongsak/uicollectionview-with-autosizing-cell-using-autolayout-in-ios-9-10-84ab5cdf35a2:

Answer 2

Based on ale84's answer and because of the fact I needed that iOS 12 fix in multiple places I created a UICollectionViewCell extension which I named UICollectionViewCell+iOS12:

extension UICollectionViewCell {     /// This is a workaround method for self sizing collection view cells which stopped working for iOS 12     func setupSelfSizingForiOS12(contentView: UIView) {         contentView.translatesAutoresizingMaskIntoConstraints = false         let leftConstraint = contentView.leftAnchor.constraint(equalTo: leftAnchor)         let rightConstraint = contentView.rightAnchor.constraint(equalTo: rightAnchor)         let topConstraint = contentView.topAnchor.constraint(equalTo: topAnchor)         let bottomConstraint = contentView.bottomAnchor.constraint(equalTo: bottomAnchor)         NSLayoutConstraint.activate([leftConstraint, rightConstraint, topConstraint, bottomConstraint])     } } 

And then in your collection view cells we do something like this (if your cell is created in IB):

override func awakeFromNib() {     super.awakeFromNib()     if #available(iOS 12, *) { setupSelfSizingForiOS12(contentView: contentView) } }