UICollectionViewCompositionalLayout + Carousel

UICollectionViewCompositionalLayoutGenerator.swift

struct LayoutGenerator {
    static func generate(handler: @escaping (Int) -> NSCollectionLayoutSection?) -> UICollectionViewCompositionalLayout {
        return .init { section, environment in
            handler(section)
        }
    }
}

struct SectionLayoutGenerator {
    static func carousel(width: CGFloat, height: CGFloat, spacing: CGFloat = 8) -> NSCollectionLayoutSection {
        let item = NSCollectionLayoutItem(
            layoutSize: .init(
                widthDimension: .fractionalWidth(1),
                heightDimension: .fractionalHeight(1)
            )
        )
        let group = NSCollectionLayoutGroup.horizontal(
            layoutSize: .init(
                widthDimension: .absolute(width),
                heightDimension: .absolute(height)
            ),
            subitems: [item]
        )
        let section = NSCollectionLayoutSection(group: group)
        section.orthogonalScrollingBehavior = .continuous
        section.interGroupSpacing = spacing
        section.contentInsets = .init(top: 0, leading: 20, bottom: 0, trailing: 20)
        return section
    }
}

Usage.swift

private func createLayout() -> UICollectionViewLayout {
    LayoutGenerator.generate { section in
        // section: Intなので場合分けができる
        return SectionLayoutGenerator.carousel(width: 100, height: 100)
    }
}

override func viewDidLoad() {
    super.viewDidLoad()
    collectionView.collectionViewLayout = createLayout()
}