如何使 UICollectionView 透明？

Question

I have tried virtually (literally?) everything to make a horizontal collection view transparent which is overlaid on a map view.

This is my collection view:

fileprivate let restaurantCollection : UICollectionView = {
        let layout = UICollectionViewFlowLayout()
        layout.scrollDirection = .horizontal
        layout.minimumInteritemSpacing = 0
        layout.minimumLineSpacing = 0
        let restaurant = UICollectionView(frame: .zero, collectionViewLayout: layout)
        restaurant.decelerationRate = .fast
        restaurant.backgroundView = nil
        restaurant.layer.backgroundColor = UIColor.clear.cgColor
        restaurant.backgroundColor = .clear
        restaurant.translatesAutoresizingMaskIntoConstraints = false
        restaurant.register(MapCell.self, forCellWithReuseIdentifier: "Cell")
        return restaurant
    }()

As you can see it has a clear background, clear layer and the background view is nil.

And the cell is transparent as well:

func setupView() {
    contentView.backgroundColor = UIColor.clear.withAlphaComponent(0)

    contentView.addSubview(cellBackground)
    cellBackground.translatesAutoresizingMaskIntoConstraints = false
    cellBackground.topAnchor.constraint(equalTo: contentView.topAnchor).isActive = true
    cellBackground.leadingAnchor.constraint(equalTo: contentView.leadingAnchor).isActive = true
    cellBackground.trailingAnchor.constraint(equalTo: contentView.trailingAnchor).isActive = true
    cellBackground.bottomAnchor.constraint(equalTo: contentView.bottomAnchor).isActive = true
    }

I also added a view to the cell "backgroundView" that's pinned with constant 0 to all sides. And this too is clear.

lazy var cellBackground : UIView = {
    let view = UIView(frame: CGRect(x: 10, y: 6, width: self.frame.width, height: 220))
    view.clipsToBounds = true
    view.backgroundColor = .clear
    view.layer.backgroundColor = UIColor.clear.cgColor
    return view
}()

And after all that effort, the collection view still has a white background

View hierarchy: Here is the view that is still white

Answer 1

You need to make sure that you are setting backgroundColor to clear

    self.collectionView.backgroundColor = UIColor.clear
    self.collectionView.backgroundView = UIView.init(frame: CGRect.zero)

Answer 2

For Modern List Layout CollectionViews:

UICollectionLayoutListConfiguration.backgroundColor = .clear
UICollectionViewListCell.backgroundConfiguration = .clear()