ios - Swift: How to mask a UICollectionView's background to only be seen behind visible cells?

Question

Introduction

Hello,

I have added a background view with a CAGradientLayer, and my UICollectionViewCells have a hole in them to see the background. So far, it all looks great:

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The Problem

However, when I scroll to the very top (and also the very bottom) of the UICollectionView, you can see the gradient background past the top of the first cell:

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Question

What is something I can do to "mask" or "constrain" the gradient background to only being visible behind the cells, and not outside of the cell's frame/bounds?

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Edit

This solves the top part, but I'm still not sure about the overflow on the bottom:

        let header = UIView()
        header.backgroundColor = UIColor.systemBackground
        collectionView.addSubview(header)
        
        header.snp.makeConstraints { (make) in
            make.top.equalTo(self.view)
            make.left.right.equalTo(self.view)
            make.bottom.equalTo(self.collectionView.snp.top)
        }

Answer 1

等待大神答复