如何在swift 4中将集合视图单元格高度缩放到屏幕大小？

Question

我有一个集合视图，当我在更大屏幕上运行应用程序时，单元格的高度不会改变iPhone我使用此代码但是当我运行此代码时，我无法在我的应用程序中看到我的集合视图

请记住我的水平收藏视图包含一行

var cellWidth:CGFloat = 0
var cellHeight:CGFloat = 0
var spacing:CGFloat = 12
var numberOfColumn:CGFloat = 9


//Scale Collection View
override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()

    specialCollectionView.contentInset = UIEdgeInsets(top: spacing, left: spacing, bottom: spacing, right: spacing)

    if let flowLayout = specialCollectionView.collectionViewLayout as? UICollectionViewFlowLayout{
        cellHeight = view.frame.size.height / specialCollectionView.frame.height
        flowLayout.minimumLineSpacing = spacing
        flowLayout.minimumInteritemSpacing = spacing
    }
}

这是扩展代码

extension secondTabViewController:UICollectionViewDelegateFlowLayout{
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
    return CGSize(width: cellWidth, height: cellHeight)
      }
}