swift - UICollectionView CompositionalLayout 不调用 UIScrollDelegate

Question

这是我的问题:
1. ScrollViewDelegate 没有被调用 一旦 UICollectionView 实现了 compositionalLayout。
使用 flowLayout 和 UICollectionViewDataSource 调用 scrollView 委托(delegate)。一旦我实现了 diffable 数据源和 CompositionalLayout，就不会再调用 scrollView 委托(delegate)了。
2. collectionView.decelerationRate = .fast 被忽略 实现 CompositionalLayout 时
我的理解是 UICollectionViewDelegate 应该调用 UIScrollViewDelegate，我已经看得很远但没有运气。有人可以指出我错过了什么吗？我整合compositionalLayout错了吗？
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:更新的代码 -
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，滚动委托(delegate)方法永远不会被调用。
我仍然可以滚动，并且预期的行为应该是滚动委托(delegate)方法确实被调用，因为我有垂直反弹。
当有大约 40 个项目并且内容显然超出屏幕大小时，滚动委托(delegate)确实会被调用。
现在有趣的是，在加载我自己的布局时:

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
        
    }

滚动代表永远不会被调用。即使有 40 多个项目。
关于如何强制 UICollectionView 与其 ScrollViewDelegates 进行通信的任何想法？

Answer 1

答案是使用 visibleItemsInvalidationHandler 关闭 部分(NSCollectionLayoutSection)。
每当事件导致动画时，此处理程序都会接收更新。它的操作类似于 scrollViewDidScroll在水平滚动组上，它将传递所有项目、 ScrollView 偏移量和 NSCollectionLayoutEnvironment。
https://developer.apple.com/documentation/uikit/nscollectionlayoutsection/3199096-visibleitemsinvalidationhandler
例子:

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