How to calculate iOS 11 size in different orientation?

Question

I calculate itemSize dependent on safe area for UICollectionView with horizontal scroll and custom layout.

Answer 1

Use UICollectionViewDelegateFlowLayout's collectionView(_:layout:sizeForItemAt:). Works like a charm. Setting the size in the completion block of coordinator.animate(alongsideTransition:completion:) in viewWillTransition(to:with:) didn't work for me because the size animation occurs after the orientation animation ends, which looks weird.