Collection view cell scrollToItem cast fails [Swift]

Question

In my swift app I've a collection view with a lot of items, I want to scroll to an item and then set a propriety of the collectionview cell custom class, but the cast fails, why? Here's my code, I've omitted some obviously steps, but the result is printing of "Cast fails":

class ViewController: UIViewController {

lazy var collectionView: UICollectionView = {
    let cv = UICollectionView(frame: self.view.bounds, collectionViewLayout: UICollectionViewFlowLayout())
    cv.backgroundColor = .gray
    cv.register(Cell.self, forCellWithReuseIdentifier: Cell.id)
    cv.delegate = self
    cv.dataSource = self
    return cv
}()

}

extension ViewController: UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: Cell.id, for: indexPath) as! Cell
    cell.backgroundColor = .purple
    cell.label.text = "\(indexPath)"
    return cell
}

func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
    if indexPath.item == 14 {
        collectionView.scrollToItem(at: IndexPath(item: 1, section: 0), at: .top, animated: true)
        guard let cell = collectionView.cellForItem(at: IndexPath(item: 1, section: 0)) as? Cell else {
            print("Cast fails")
            return
        }
        cell.label.text = "Something"
    }
}

}

Here's the solution I found:

extension UICollectionView {
    func scrollToItem(at indexPath: IndexPath, at position: UICollectionView.ScrollPosition, completion: @escaping () -> ()) {
        scrollToItem(at: indexPath, at: .top, animated: true)
        DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) {
            completion()
        }
    }
}

Answer 1

The cast fails as the cell ( of that specific index ) is not visible at the moment you query for it

guard let cell = collectionView.cellForItem(at: IndexPath(item: 1, section: 0)) as? Cell else {
  print("Cast fails")
  return
} 

instead you can try to set , at: .top, animated: false) or wrap the above code snippet inside a Dispatch after block

Btw you should better change the dataSource array and reload that index and that way you don't need a wait

// change source array at that index
// scroll to that row with/without animation
// make sure you set value for the cell label in cellForRowAt table's datasource method