问带全页单元格的UICollectionView与带有子视图控制器的UIScrollView

EN

....
var childrenVC: [Int: UIViewController] = [:]
....
// cell for row
let cell: ChildControllerCell = collectionView.dequeueReusableCell(for: indexPath)
if let childController = childrenVC[indexPath.row] {
   cell.contentView.addSubview(childController.view)
   childController.view.frame = cell.contentView.frame
} else {
   let childViewController = ChildViewController()
   addChildViewController(childViewController)
   childViewController.didMove(toParentViewController: self)
   cell.contentView.addSubview(childController.view)
   childController.view.frame = cell.contentView.frame
   childrenVC[indexPath.row] = childViewController
   cell.childVC = childViewController
}
return cell
....
class ChildControllerCell: UICollectionViewCell {
     var childVC: UIViewController?
     override func prepareForReuse() {
        super.prepareForReuse()
        if !contentView.subviews.isEmpty {
            childVC?.willMove(toParentViewController: nil)
            childVC?.view.removeFromSuperview()
            childVC?.removeFromParentViewController()
        }
    }
}