UICollectionViewCell not shown properly - swift

Question

I have the following code. For some strange reason, the cell is not registering properly and the cell is not rendered.
I expect there to be 5 purple cells but instead there is only red background.
class RateController: UICollectionViewController {
var user: User?
let cellId = "cellId"
override func viewDidLoad() {
super.viewDidLoad()
collectionView?.backgroundColor = .red
collectionView?.register(UICollectionViewCell.self, forCellWithReuseIdentifier: cellId)
}
override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return 5
}
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellId, for: indexPath)
cell.backgroundColor = .purple
return cell
}
}

Answer 1

There's nothing wrong with your code. I pasted it right into a fresh project, defined the User class, made the necessary adjustments in the storyboard, and ran it:
So if there's a problem, it's somewhere else — not in that code!
I've been thinking about where else the problem could be; the problem you are describing would happen if you disabled the Flow layout in the storyboard and replaced it with an empty Custom layout, like this:
If you did that, set the Layout back to Flow.