ios - 具有估计高度的 CollectionView 组合布局仅显示 _UICollectionViewOrthogonalScrollerEmbeddedScrollView

Question

我有一个复杂的布局，大部分时间它加载得很好。重新加载几次后，虽然一切都消失了（这并不总是发生），我只看到一个空的 collectionView。如果我检查它，我可以看到只有空空间和多个 _UICollectionViewOrthogonalScrollerEmbeddedScrollView （可以看到下面的布局检查器）。

控制台中的唯一警告与项目插图有关，但我不确定它是否甚至相关，因为插图不适用于具有垂直滚动的组合 collectionView，但我认为它不会导致其他问题那。即使 collectionView 显示正常，警告仍然存在。

当问题发生时，collectionView 设置正确，甚至检查它，您可以看到节和行的数量设置正确。如果我在单元格被填充的位置放置一个断点，尽管它没有被调用。

部分布局示例：

func generateSideBySideAdaptiveLayout(isWide: Bool, height: CGFloat, withHeader header: Bool, numberOfItems: Int, withFooter footer: Bool = false, direction: UICollectionViewAdaptiveLayoutSectionDirection = .vertical) -> NSCollectionLayoutSection {

    let itemSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1.0),
                                          heightDimension: .estimated(height))
    let item = NSCollectionLayoutItem(layoutSize: itemSize)

    // Show one item on narrow screens, two items on wider screens
    let groupFractionalWidth = isWide ? 0.5 : 1
    let groupHeight = isWide ? height : height * CGFloat(numberOfItems)
    let groupSize = NSCollectionLayoutSize(
        widthDimension: .fractionalWidth(CGFloat(groupFractionalWidth)),
        heightDimension: .estimated(CGFloat(groupHeight)))
    let group: NSCollectionLayoutGroup
    switch direction {
    case .vertical:
        group = isWide ? NSCollectionLayoutGroup.vertical(layoutSize: groupSize, subitem: item, count: numberOfItems / 2) : NSCollectionLayoutGroup.vertical(layoutSize: groupSize, subitem: item, count: numberOfItems)
    case .horizontal:
        group = isWide ? NSCollectionLayoutGroup.horizontal(layoutSize: groupSize, subitem: item, count: numberOfItems) : NSCollectionLayoutGroup.horizontal(layoutSize: groupSize, subitem: item, count: numberOfItems)
    }

    let section = NSCollectionLayoutSection(group: group)
    
    var supplementary: [NSCollectionLayoutBoundarySupplementaryItem] = []
    
    let headerSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1.0),
                                            heightDimension: .estimated(44))
    if header {
        
        let sectionHeader = NSCollectionLayoutBoundarySupplementaryItem(
            layoutSize: headerSize,
            elementKind: SectionHeader.title.rawValue, alignment: .top)
        supplementary.append(sectionHeader)
    }
    if footer {
        let sectionFooter = NSCollectionLayoutBoundarySupplementaryItem(
            layoutSize: headerSize,
            elementKind: SectionFooter.actionButton.rawValue,
            alignment: .bottom)
        supplementary.append(sectionFooter)
    }
    section.boundarySupplementaryItems = supplementary
    section.orthogonalScrollingBehavior = .groupPaging

    return section
}

数据设置代码示例：

var snapshot = NSDiffableDataSourceSnapshot<FeedCollectionSection, FeedCollectionItem>()
    guard sections.count > 0 else {
        return snapshot
    }
    
    snapshot.appendSections(sections)
    
    for each in sections {
        let items = getItemsForSection(each)
        snapshot.appendItems(items, toSection: each)
    }
    
    return snapshot