UICollectionViewCompositionalLayout 部分中的两组

Question

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我使用 UICollectionViewCompositionalLayout 创建 UICollectionView，我希望第一个 Item 占据宽度的一半，其他 Item 占据宽度的 1/4，项目向下增长，如下所示：

https://i.sstatic.net/uO5R9.png

但我无法实现两个组的共存部分，这是我的代码：

    let compositionalLayout: UICollectionViewCompositionalLayout = {
        let inset: CGFloat = 1

        // Items
        let largeItemSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(0.5), heightDimension: .fractionalHeight(1))
        let largeItem = NSCollectionLayoutItem(layoutSize: largeItemSize)
        largeItem.contentInsets = NSDirectionalEdgeInsets(top: inset, leading: inset, bottom: inset, trailing: inset)

        let smallItemSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(0.5), heightDimension: .fractionalHeight(1))
        let smallItem = NSCollectionLayoutItem(layoutSize: smallItemSize)
        smallItem.contentInsets = NSDirectionalEdgeInsets(top: inset, leading: inset, bottom: inset, trailing: inset)

        let smallItemGroupSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .fractionalHeight(0.5))
        let smallItemGroup = NSCollectionLayoutGroup.horizontal(layoutSize: smallItemGroupSize, subitems: [smallItem])

        // Nested Group
        let nestedGroupSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(0.5), heightDimension: .fractionalHeight(1))
        let nestedGroup = NSCollectionLayoutGroup.vertical(layoutSize: nestedGroupSize, subitems: [smallItemGroup])

        // Outer Group
        let outerGroupSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .fractionalWidth(0.5))
        let outerGroup = NSCollectionLayoutGroup.horizontal(layoutSize: outerGroupSize, subitems: [largeItem, nestedGroup])

        // Section
        let section = NSCollectionLayoutSection(group: outerGroup)
        section.contentInsets = NSDirectionalEdgeInsets(top: inset, leading: inset, bottom: inset, trailing: inset)

        // Supplementary Item
        let headerItemSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .absolute(40))
        let headerItem = NSCollectionLayoutBoundarySupplementaryItem(layoutSize: headerItemSize, elementKind:  UICollectionView.elementKindSectionHeader, alignment: .top)
        section.boundarySupplementaryItems = [headerItem]

        let layout = UICollectionViewCompositionalLayout(section: section)

        return layout
    }()

https://i.sstatic.net/i88Q2.png

我应该如何使用UICollectionViewCompositionalLayout来达到图1的效果。