Swift: Collection View changing layout after rotation - ios

Question

I have a collection view with 6 items and want to display them in a 2 cells per row and 3 rows format. The following code achieves this (as taken from this question: Swift: Collection View not adjusting correctly to change in size) in iPhone format nicely.
However on the any iPad the views layout is correct initially but if the screen is rotated to landscape and then back to portrait then the layout does not fully fit within the view and requires horizontal scrolling to see the second cell (cells width has somehow increased meaning the second cell in each row is partially cut off).
override func viewDidLoad() {
super.viewDidLoad()
collectionView.dataSource = self
collectionView.delegate = self
flowLayout.scrollDirection = .horizontal
flowLayout.minimumLineSpacing = 5
flowLayout.minimumInteritemSpacing = 5
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return 6
}
override func willRotate(to toInterfaceOrientation: UIInterfaceOrientation, duration: TimeInterval) {
self.collectionView.collectionViewLayout.invalidateLayout()
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
if UIDevice.current.orientation.isLandscape {
let totalWidth = collectionView.frame.width
let totalHeight = collectionView.frame.height
let heightOfCell = totalHeight / 2
let numberOfCellsPerRow = 1
let widthOfCell = CGFloat(Int(totalWidth) / numberOfCellsPerRow)
return CGSize(width: widthOfCell , height: heightOfCell)
} else {
let totalWidth = collectionView.frame.width
let totalHeight = collectionView.frame.height
let heightOfCell = (totalHeight / 3)
let numberOfCellsPerRow = 2
let widthOfCell = CGFloat(Int(totalWidth) / numberOfCellsPerRow)
return CGSize(width: widthOfCell , height: heightOfCell)
}
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAt section: Int) -> UIEdgeInsets {
return UIEdgeInsetsMake(0, 5, 0, 5)
}

Answer 1

The problem here appears to be that, frame of the view is not updated when 'willRotate' is invoked. Instead try 'didrotate' or add the observer 'NSNotification.Name.UIDeviceOrientationDidChange' and invalidateLayout of collection inside the selector method. Don't forget to remove the observer on deinit().