如何在 iOS 13 集合视图组合布局上隐藏标题

Question

我在部署 iOS 13 组合布局时遇到了一个奇点。

我想隐藏集合视图标题并实现referenceSizeForHeaderInSection 方法，但是referenceSizeForHeaderInSection 不能在组合布局上工作

这是我的构图布局：

lazy var collectionViewLayout: UICollectionViewLayout = {
    // item layout deploy
    let cellItemSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1.0), heightDimension: .fractionalHeight(0.2))
    let itemSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(0.33), heightDimension: .fractionalHeight(1.0))
    let cellItem = NSCollectionLayoutItem(layoutSize: cellItemSize)
    let item = NSCollectionLayoutItem(layoutSize: itemSize)
    cellItem.contentInsets = NSDirectionalEdgeInsets(top: 4, leading: 4, bottom: 4, trailing: 4)
    item.contentInsets = NSDirectionalEdgeInsets(top: 4, leading: 4, bottom: 4, trailing: 4)

    // group layout deploy
    let groupSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1.0),  heightDimension: .fractionalHeight(0.2))
    let group = NSCollectionLayoutGroup.horizontal(layoutSize: groupSize, subitem: item, count: 3)
    let containerGroupSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1.0),  heightDimension: .absolute(215))
    let containerGroup = NSCollectionLayoutGroup.vertical(layoutSize: containerGroupSize, subitems: [cellItem, group, group, group, group])

    // section layout deploy
    let section = NSCollectionLayoutSection(group: containerGroup)
    section.contentInsets = NSDirectionalEdgeInsets(top: 4, leading: 0, bottom: 4, trailing: 0)

    // Headers layout deploy
    let headerSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1.0), heightDimension: .absolute(18))
    let header = NSCollectionLayoutBoundarySupplementaryItem(layoutSize: headerSize, elementKind: SupplementaryViewOfKind.Header.rawValue, alignment: .top)
    section.boundarySupplementaryItems = [header]

    let layout = UICollectionViewCompositionalLayout(section: section)

    return layout
}()

实现viewForSupplementaryElementOfKind

func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {
    guard
        kind == SupplementaryViewOfKind.Header.rawValue,
        let header = collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: XXXHeader.identifier, for: indexPath) as? XXXHeader
        else { return UICollectionReusableView() }
    if isFullScreen {
        // customer header with titleLabel property
        header.titleLabel.text = segmentedControl.titleForSegment(at: indexPath.section)
    } else {
        header.titleLabel.text = nil
    }
}

然后我尝试进入referenceSizeForHeaderInSection，但无法工作

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, referenceSizeForHeaderInSection section: Int) -> CGSize {
    if isFullScreen {
        return CGSize(width: collectionView.frame.width, height: 18)
    } else {
        return CGSize.zero
    }
}

有什么想法或新方法可以隐藏合成布局标题。

Answer 1

func configureDiffableDataSource() {
    let dataSource = UICollectionViewDiffableDataSource<TripSection, TripItem>(collectionView: collectionView) {
        (collectionView: UICollectionView, indexPath: IndexPath, item: TripItem) -> UICollectionViewCell? in
      let cell = collectionView.dequeueCell(ofType: SmallTableViewCell.self, for: indexPath)
      cell.fillWithData(tip)
       return cell
        }
    }

//添加 elementKindSectionHeader if isFullScreen return nil

    dataSource.supplementaryViewProvider = { [weak self] (collectionView: UICollectionView, kind: String, indexPath: IndexPath) -> UICollectionReusableView? iln
        guard let itamSequence = self?.dataSource?.itemIdentifier(for: indexPath) else { return nil }
        guard let section = self?.dataSource?.snapshot().sectionIdentifier(containingItem: itamSequence) else { return nil }
       let boardHeader = collectionView.dequeueReusableView(ofType: BoardSupplementaryView.self, forKind: UICollectionView.elementKindSectionHeader, for: indexPath)
         return boardHeader
        }
    }

     self.dataSource = dataSource
     updateSnapshot(animated: false)
}

Answer 2

我做什么：

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, referenceSizeForHeaderInSection section: Int) -> CGSize {
    if needHideHeaderView {
        if let headerView = collectionView.supplementaryView(forElementKind: UICollectionView.elementKindSectionHeader, at: IndexPath(row: 0, section: section)) {
            headerView.isHidden = true
        }
        return CGSize.zero
    } else {
       // other code
    }

Answer 3

在生成布局时，可以传入索引

func generateLayout() -> UICollectionViewLayout {
    let layout = UICollectionViewCompositionalLayout {(sectionIndex: Int, layoutEnvironment: NSCollectionLayoutEnvironment) -> NSCollectionLayoutSection? in
        // do your layout stuff here. With sectionIndex, you can layout differently for each section
    }
    return layout
}

Answer 4

目前，除了创建自己的协议来确定是否应在部分中显示标题之外，似乎没有其他方法可以做到这一点。幸运的是，UICollectionViewCompositionalLayout 构造函数为我们提供了节索引，因此很容易做到。不要为没有它们的部分创建任何补充视图。

protocol CollectionViewLayoutProviderDelegate: class {
    func layoutProvider(_ provider: CollectionViewLayoutProvider, shouldDisplaySupplementaryViewIn section: Int) -> Bool
}

class CollectionViewLayoutProvider {
    weak var delegate: CollectionViewLayoutProviderDelegate?
    init(delegate: CollectionViewLayoutProviderDelegate?) {
        self.delegate = delegate
    }
    
    private func prepareSupplementaryViews(section: Int) -> [NSCollectionLayoutBoundarySupplementaryItem] {
        if let delegate = delegate,
           !delegate.layoutProvider(self, shouldDisplaySupplementaryViewIn: section) {
// Return empty array to avoid displaying headers

            return []
        }
        // Configure header if you need to
    }
    
    private func prepareSection(section: Int, group: NSCollectionLayoutGroup) -> NSCollectionLayoutSection {
        let layoutSection = NSCollectionLayoutSection(group: group)
        layoutSection.boundarySupplementaryItems = prepareSupplementaryViews(section: section)
        
        return layoutSection
    }
}

然后，在您的视图控制器中

private lazy var layoutProvider = CollectionViewLayoutProvider(delegate: self)

extension YouViewController: CollectionViewLayoutProviderDelegate {
    func layoutProvider(_ provider: CollectionViewLayoutProvider, shouldDisplaySupplementaryViewIn section: Int) -> Bool {
        return viewModel.shouldDisplayHeader(for: section) != nil
    }
}