根据选择的UITextField滚动UICollectionViewCell Swift 3

var selectedTextField: UITextField?

func textFieldDidBeginEditing(_ textField: UITextField) {
    selectedTextField = textField
}

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    guard let selectedTextField = selectedTextField else {
        return
    }
    
    let visibleRect = CGRect(origin: collectionView.contentOffset, size: collectionView.bounds.size)
    let visibleCells = collectionView.visibleCells
    
    for cell in visibleCells {
        if let textField = cell.contentView.subviews.first(where: { $0 is UITextField }) as? UITextField {
            if textField == selectedTextField {
                let cellRect = collectionView.convert(cell.frame, to: collectionView.superview)
                let textFieldRect = textField.convert(textField.bounds, to: collectionView.superview)
                
                if !visibleRect.contains(cellRect) || !visibleRect.contains(textFieldRect) {
                    collectionView.scrollRectToVisible(cellRect, animated: true)
                }
                
                break
            }
        }
    }
}