How to determine when a custom UICollectionViewCell is 100% on the screen

Question

From the diagram above I have UICollectionView with 4 custom cells. At any time 2 or three cells can be on the screen. How can I tell when \"cell 1\"

Answer 1

Here's an extension for it, based don DonMag's answer:

extension UICollectionView {
    var fullyVisibleCells : [UICollectionViewCell] {
        return self.visibleCells.filter { cell in
            let cellRect = self.convert(cell.frame, to: self.superview)
            return self.frame.contains(cellRect) }
    }
}