UICollectionView CompositionalLayout 不调用 UIScrollDelegate

Question

这是我的问题：

1。一旦 UICollectionView 实现了 compositionalLayout，ScrollViewDelegate 就不会被调用。

使用 flowLayout 和 UICollectionViewDataSource 调用 scrollView 委托。一旦我实现了 diffable 数据源和 CompositionalLayout，scrollView 委托就不会再被调用了。

2。 collectionView.decelerationRate = .fast 在实现 CompositionalLayout

时被忽略

我的理解是 UICollectionViewDelegate 应该调用 UIScrollViewDelegate，我看了很远但没有运气。有人可以指出我错过了什么吗？我是不是把 compositionalLayout 整合错了？

这是我的代码：



import UIKit

class ViewController: UIViewController, UICollectionViewDelegate, UIScrollViewDelegate {
    
    enum Section {
        case weekdayHeader
    }
    
    @IBOutlet weak var collectionView: UICollectionView!
    
    let weekdays = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday","Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"]
    
    var weekdaysArr = [Weekdays]()
    
    var dataSource: UICollectionViewDiffableDataSource<Section, Weekdays>! = nil
    
    private let cellReuseIdentifier = "myCell"
    
    
    
    override func viewDidLoad() {
        super.viewDidLoad()
        self.collectionView.delegate = self
        self.collectionView.register(UINib(nibName: "MyCollectionViewCell", bundle: nil), forCellWithReuseIdentifier: cellReuseIdentifier)
        self.collectionView.decelerationRate = .normal
        
        configureCollectionView()
        configureDataSource()
        configureWeekdays()
        updateCollectionView()
        
        // Do any additional setup after loading the view.
    }
    
    func configureCollectionView(){
        self.collectionView.delegate = self
        self.collectionView.collectionViewLayout = generateLayout()
    }
    
    func generateLayout() -> UICollectionViewLayout {
        
        let itemSize = NSCollectionLayoutSize(
            widthDimension: .estimated(10),
            heightDimension: .fractionalHeight(1))
        let weekdayItem = NSCollectionLayoutItem(layoutSize: itemSize)
        //        weekdayItem.contentInsets = NSDirectionalEdgeInsets(top: 5, leading: 50, bottom: 5, trailing: 50)
        
        let groupSize = NSCollectionLayoutSize(
            widthDimension: .fractionalWidth(0.3),
            heightDimension: .fractionalHeight(1.0))
        let group = NSCollectionLayoutGroup.vertical(layoutSize: groupSize, subitems: [weekdayItem])
        
        //        let spacing = CGFloat(10)
        //        group.interItemSpacing = .fixed(spacing)
        
        let section = NSCollectionLayoutSection(group: group)
        section.interGroupSpacing = CGFloat(20)
        section.contentInsets = NSDirectionalEdgeInsets(top: 0, leading: 0, bottom: 0, trailing: 500)
        section.orthogonalScrollingBehavior = .continuousGroupLeadingBoundary
        
        
        
        
        let layout = UICollectionViewCompositionalLayout(section: section)
        
        return layout
        
    }
    
    func configureDataSource() {
        dataSource = UICollectionViewDiffableDataSource
            <Section, Weekdays>(collectionView: collectionView)
            { (collectionView: UICollectionView, indexPath: IndexPath, weekday: Weekdays) -> UICollectionViewCell? in
                guard let cell = collectionView.dequeueReusableCell(withReuseIdentifier: self.cellReuseIdentifier, for: indexPath) as? MyCollectionViewCell else {
                    fatalError("Cannot create a new cell") }
                cell.titleLabel.text = weekday.name
                print("weekday.name = \(weekday.name)")
                return cell
        }
        //      let snapshot = snapshotForCurrentState()
        //      dataSource.apply(snapshot, animatingDifferences: false)
    }
    
    func configureWeekdays(){
        
        weekdaysArr.append(Weekdays(name: "Monday"))
        weekdaysArr.append(Weekdays(name: "Tuesday"))
        weekdaysArr.append(Weekdays(name: "Wednesday"))
        weekdaysArr.append(Weekdays(name: "Thursday"))
        weekdaysArr.append(Weekdays(name: "Friday"))
        weekdaysArr.append(Weekdays(name: "Saturday"))
        weekdaysArr.append(Weekdays(name: "Sunday"))
        
    }
    
    func updateCollectionView(){
        var snapshot = NSDiffableDataSourceSnapshot<Section, Weekdays>()
        snapshot.appendSections([.weekdayHeader])
        snapshot.appendItems(weekdaysArr, toSection: .weekdayHeader)
        dataSource.apply(snapshot, animatingDifferences: false)
    }
    
    
    
    //MARK: Scroll View Delegate
    
    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        print("ScrollView decel rate: \(scrollView.decelerationRate)")
    }
    
    public func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
        print("Begin")
    }
    
    func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
        print("End")
    }
    
    func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) {
        print("END")
    }
    
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
          
          print("Did select a cell here")
          
         }
    
    
}

struct Weekdays: Hashable {
    let identifier: UUID = UUID()
    let name: String
    
    func hash(into hasher: inout Hasher){
        return hasher.combine(identifier)
    }
    
    static func == (lhs: Weekdays, rhs: Weekdays) -> Bool {
        return lhs.identifier == rhs.identifier
    }
}

谢谢

编辑：更新代码 -

编辑：与来自 WWDC 的 Apple 示例代码进行比较，我发现了这种行为。

如果我使用示例代码网格布局

func gridLayout() -> UICollectionViewLayout {
        let itemSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(0.2),
                                             heightDimension: .fractionalHeight(1.0))
        let item = NSCollectionLayoutItem(layoutSize: itemSize)

        let groupSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1.0),
                                              heightDimension: .fractionalWidth(0.2))
        let group = NSCollectionLayoutGroup.horizontal(layoutSize: groupSize,
                                                         subitems: [item])

        let section = NSCollectionLayoutSection(group: group)

        let layout = UICollectionViewCompositionalLayout(section: section)
        return layout
    }

当只有 7 个项目时，Scroll Delegate 方法永远不会被调用。

我仍然可以滚动，预期的行为应该是滚动委托方法确实被调用，因为我有垂直弹跳。

当有大约 40 个项目并且内容明显超出屏幕尺寸时，滚动委托会被调用。

加载我自己的布局时有趣的是：

func generateLayout() -> UICollectionViewLayout {
        
        let itemSize = NSCollectionLayoutSize(
            widthDimension: .estimated(10),
            heightDimension: .fractionalHeight(1))
        let weekdayItem = NSCollectionLayoutItem(layoutSize: itemSize)
        //        weekdayItem.contentInsets = NSDirectionalEdgeInsets(top: 5, leading: 50, bottom: 5, trailing: 50)
        
        let groupSize = NSCollectionLayoutSize(
            widthDimension: .fractionalWidth(0.3),
            heightDimension: .fractionalHeight(1.0))
        let group = NSCollectionLayoutGroup.vertical(layoutSize: groupSize, subitems: [weekdayItem])
        
        //        let spacing = CGFloat(10)
        //        group.interItemSpacing = .fixed(spacing)
        
        let section = NSCollectionLayoutSection(group: group)
        section.interGroupSpacing = CGFloat(20)
        section.contentInsets = NSDirectionalEdgeInsets(top: 0, leading: 0, bottom: 0, trailing: 500)
        section.orthogonalScrollingBehavior = .continuousGroupLeadingBoundary
        
        
        
        
        let layout = UICollectionViewCompositionalLayout(section: section)
        
        return layout
        
    }

Scroll 委托永远不会被调用。即使有 40 多个项目。

关于如何强制 UICollectionView 与其 ScrollViewDelegates 通信的任何想法？

Answer 1

似乎是 UICollectionView 组合布局中水平滚动组的意外行为

以防其他人遇到同样的问题。这似乎是水平滚动组合布局组的问题。

只有垂直滚动组会触发 UIScrollViewDelegates。

不幸的是，这也意味着似乎decelerationrate.fast不能应用于水平滚动。它只会被忽略。

重现问题的步骤和分析

可以通过在此处的 wwdc 示例代码 "Advancements in Collection View Layout" 中实施 UIScrollViewDelegate 方法来重新创建此行为：https://developer.apple.com/videos/play/wwdc2019/215/ 在 class: OrthogonalScrollBehaviorViewController.swift 中，我们找到水平和垂直滚动组。

结论

UIScrollViewDelegate 只与垂直滚动组交互。水平滚动组不与集合视图的滚动委托通信。

如果在水平滚动组中需要滚动委托方法，那么仍然需要使用嵌套 CollectionView 和 FlowLayout/自定义布局的传统方法。

备注

如果有人能向我指出我遗漏了什么，我将非常感激，直到那时这将作为我上述问题的答案。

感谢所有发表评论的人。

Answer 2

答案是在 (NSCollectionLayoutSection) 部分使用 visibleItemsInvalidationHandler 闭包。

只要事件导致动画，此处理程序就会收到更新。它的操作类似于 scrollViewDidScroll 并且在水平滚动组上它将传递所有项目、滚动视图偏移量和 NSCollectionLayoutEnvironment。

https://developer.apple.com/documentation/uikit/nscollectionlayoutsection/3199096-visibleitemsinvalidationhandler

示例：

section.visibleItemsInvalidationHandler = { [weak self] visibleItems, point, environment in self?.currentIndex = visibleItems.last?.indexPath.row }

Answer 3

代码片段：

section.visibleItemsInvalidationHandler = { [weak self] visibleItems, point, environment in
    self?.pager.currentPage = visibleItems.last!.indexPath.row
}

Answer 4

根据您的用例，您还可以使用集合视图委托方法

func collectionView(_ collectionView: UICollectionView, willDisplay cell: UICollectionViewCell, forItemAt indexPath: IndexPath)

func collectionView(_ collectionView: UICollectionView, didEndDisplayingCell cell: UICollectionViewCell, forItemAt indexPath: IndexPath)

在这些委托方法中 - 您可以在特定部分即将显示单元格时做出反应以结束显示单元格

Answer 5

如果您垂直滚动 collectionView，

UICollectionViewDelegate 将调用 scrollDidView。在我的情况下，我试图从水平滚动进行跟踪，我正在使用以下代码来使事情正常进行。

func collectionView(_ collectionView: UICollectionView, didEndDisplayingCell cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
      let visibleRect = CGRect(origin: yourCollectionView.contentOffset, size: photoCollectionView.bounds.size)
      let visiblePoint = CGPoint(x: visibleRect.midX, y: visibleRect.midY)
      let visibleIndexPath = yourCollectionView.indexPathForItem(at: visiblePoint) // Current display cell in collectionView
}

这不是这个问题的答案，但希望这对在 collectionView 组合布局中从水平滚动中搜索跟踪当前显示单元格的人有所帮助

Answer 6

我找到了一种方便的方法来处理这个问题，您可以避免设置正交滚动并使用配置来代替：

let config = UICollectionViewCompositionalLayoutConfiguration()
config.scrollDirection = .horizontal
let layout = UICollectionViewCompositionalLayout(sectionProvider:sectionProvider,configuration: config)

这将调用 collectionview 的所有滚动委托。希望这会对某人有所帮助。

UICollectionView CompositionalLayout 不调用 UIScrollDelegate

UICollectionView CompositionalLayout not calling UIScrollDelegate

uiscrollview

uicollectionview

swift