【发布时间】：2020-01-10 01:50:58
【问题描述】：
这是我的问题：
1.一旦 UICollectionView 实现了 compositionalLayout，就不会调用 ScrollViewDelegate。
使用 flowLayout 和 UICollectionViewDataSource 调用 scrollView 委托。一旦我实现了 diffable 数据源和 CompositionalLayout，就不会再调用 scrollView 委托了。
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，滚动委托方法永远不会被调用。
虽然我仍然可以滚动，但预期的行为应该是滚动委托方法确实被调用，因为我有垂直反弹。
当有大约 40 个项目并且内容明显超出屏幕大小时，滚动代理会被调用。
现在加载我自己的布局时很有趣：
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 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？
【问题讨论】：
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如果你不让类委托访问 UIScrollView，那么拥有 UIScrollView 委托方法有什么意义？
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-
搜索讨论 UIScrollView 的主题。
-
为什么当我删除组合布局时它仍然有效？不确定我的问题是否描述得不够清楚，但我认为搜索讨论 UIScrollView 的主题不会解决这个问题。我怀疑这是 CompositionalLayout 的实现。
-
你在哪里设置
self.collectionView.delegate？
标签： swift uicollectionview uiscrollview