当单元格即将离屏时，UICollectionView Cell的阴影突然消失

Question

I have a collection view with rounded and shadow-dropped cells. The shadow of the cell suddenly disappears, instead of smoothly moving out of the view, when the cell is about to be covered by the navigation bar. Below is the code:

    contentView.layer.cornerRadius = 20
    contentView.layer.masksToBounds = true

    layer.shadowColor = UIColor.black.cgColor
    layer.shadowOpacity = 0.1
    layer.shadowOffset = CGSize(width: 0, height: 5.0)
    layer.shadowRadius = 5.0
    layer.shadowPath = UIBezierPath(roundedRect: bounds, cornerRadius: contentView.layer.cornerRadius - 3).cgPath
    layer.shouldRasterize = true
    layer.rasterizationScale = UIScreen.main.scale

Here is the gif showing the problem. Focus on the shadow at the bottom of the cell. The navigation bar is white. Any help would be appreciated. Thank you!

Answer 1

I believe it's simply because the cell does really get removed from the view, thus it's shadow goes with it. At that point the frame of the cell is out of the view, while shadow is still visible (shadow is around the frame) - but when the frame goes out of view, the collectionView removes the cell. And so the shadow disappears abruptly.

What I would do about it is very simple. I would refactor the code to wrap the current cell contents into a new UIView - lets call it wrapper , that will drop the shadow. Then put this wrapper into the cell's contentView so that the wrapper along with its shadow will fit inside of the contentView . Then the shadow will become a part of the contentView frame, which means that the shadow will disappear from the screen only when the whole cell is hidden.

Of course, you will have to modify the collectionView 's size for cell, because now the cells will be bigger to contain also the shadow.

Answer 2

Instead of setting shadow of contentView embed all your content in a UIView and set shadow of that view instead. Then you have to increase the height of your cell about 20 points or as much your shadow height. That should work I guess.