Keeping the contentOffset in a UICollectionView while rotating Interface Orientation

Question

I\'m trying to handle interface orientation changes in a UICollectionViewController. What I\'m trying to achieve is, that I want to have the same contentOffset afte

Answer 1

Swift 4.2 subclass:

class RotatableCollectionViewFlowLayout: UICollectionViewFlowLayout {

    private var focusedIndexPath: IndexPath?

    override func prepare(forAnimatedBoundsChange oldBounds: CGRect) {
        super.prepare(forAnimatedBoundsChange: oldBounds)
        focusedIndexPath = collectionView?.indexPathsForVisibleItems.first
    }

    override func targetContentOffset(forProposedContentOffset proposedContentOffset: CGPoint) -> CGPoint {
        guard let indexPath = focusedIndexPath
            , let attributes = layoutAttributesForItem(at: indexPath)
            , let collectionView = collectionView else {
                return super.targetContentOffset(forProposedContentOffset: proposedContentOffset)
        }
        return CGPoint(x: attributes.frame.origin.x - collectionView.contentInset.left,
                       y: attributes.frame.origin.y - collectionView.contentInset.top)
    }

    override func finalizeAnimatedBoundsChange() {
        super.finalizeAnimatedBoundsChange()
        focusedIndexPath = nil
    }
}