UICollectionViewCell doesn't fill the screen - ios

Question

I have a UIViewController containing a UICollectionView for vertical paging. The UICollectionView (blue area in the picture) is pinned to the top of the superview, but UICollectionViewCell (yellow) is not. I tried to explicitly pin the top constraint of the UICollectionViewCell to the top of UICollectionView but the program crashes.
class HomeViewController: UIViewController, UICollectionViewDelegateFlowLayout {
override func viewDidLoad() {
super.viewDidLoad()
let collectionView = UICollectionView(frame: CGRect.zero, collectionViewLayout: UICollectionViewFlowLayout())
collectionView.register(FeedCell.self, forCellWithReuseIdentifier: reuseIdentifier)
collectionView.backgroundColor = .blue
collectionView.showsVerticalScrollIndicator = false
collectionView.isPagingEnabled = true
view.addSubview(collectionView)
collectionView.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate([
collectionView.topAnchor.constraint(equalTo: view.topAnchor),
collectionView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
view.bottomAnchor.constraint(equalTo: collectionView.bottomAnchor),
view.trailingAnchor.constraint(equalTo: collectionView.trailingAnchor)
])
collectionView.dataSource = self
collectionView.delegate = self
}
override var preferredStatusBarStyle: UIStatusBarStyle {
.lightContent
}
// MARK: UICollectionViewDelegateFlowLayout
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
return CGSize(width: view.frame.width, height: collectionView.bounds.height)
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumInteritemSpacingForSectionAt section: Int) -> CGFloat {
return 0
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAt section: Int) -> CGFloat {
return 0
}
}
extension HomeViewController: UICollectionViewDataSource {
func numberOfSections(in collectionView: UICollectionView) -> Int {
1
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
4
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath)
cell.backgroundColor = indexPath.item % 2 == 0 ? .yellow : .orange
return cell
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAt section: Int) -> UIEdgeInsets {
return UIEdgeInsets(top: 0, left: 0, bottom: 0, right: 0)
}
}

Answer 1

Just pin your collection view to the top of View, not to the safeArea
collectionView.topAnchor.constraint(equalTo: view.topAnchor).isActive = true;
And use to just your collection view to safe area insets:
collectionView.contentInsetAdjustmentBehavior = .never;

Answer 2

Instead of pinning to all safe area edges using pinEdgesToSafeArea(to:) you should pin the top constraint of the collection view to the top constraint of view. I don't know where pinEdgesToSafeArea(to:) comes from so can't comment on a replacement for that but you can use this to pin your collection view to the top of the screen:
collectionView.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
Edit:
based on the clarifications you've posted, try setting automaticallyAdjustsScrollIndicatorInsets to false:
collectionView.automaticallyAdjustsScrollIndicatorInsets = false
docs for more info