这就是如何使用UICollectionViewFlowLayout在代码中创建它

let layout = UICollectionViewFlowLayout()
layout.scrollDirection = .vertical
let collectionView = UICollectionView(frame: frame, collectionViewLayout: layout)

或者如果您正在使用现有的集合视图，

if let layout = collectionView.collectionViewLayout as? UICollectionViewFlowLayout {
    layout.scrollDirection = .vertical
}

如果使用UICollectionViewCompositionalLayout
UICollectionViewCompositionalLayoutConfiguration具有scrollDirection属性。更改它将影响整个集合视图。如果需要，您还可以为每个部分设置单独的滚动方向。

let configuration = UICollectionViewCompositionalLayoutConfiguration()
configuration.scrollDirection = .vertical

collectionView.collectionViewLayout = UICollectionViewCompositionalLayout(
    sectionProvider: { section, environment in
        // Return section
    },
    configuration: configuration
)

如果你没有使用故事板，一切都是通过编程完成的。所以当我们这样做时：

lazy var snapCollectionView: UICollectionView = {
        let layout = UICollectionViewFlowLayout()
        let collectionView = UICollectionView(frame: CGRect.zero, 
        collectionViewLayout: layout)
        layout.scrollDirection = .horizontal
        collectionView.delegate = self
        collectionView.dataSource = self
        collectionView.backgroundColor = UIColor(named: "background")
        return collectionView
    }()