我的问题是:
1.一旦UICollectionView实作compositionalLayout,就不会呼叫ScrollViewDelegate。
使用flowLayout和UICollectionViewDataSource调用scrollView委托。一旦我实现了可区分的数据源和CompositionalLayout,就不再调用scrollView委托了。
2.集合视图.减速率= .fast被忽略当实现复合布局时
我的理解是UICollectionViewDelegate应该调用UIScrollViewDelegate,我已经找了很远很远的地方,但是没有找到。有人能指出我遗漏了什么吗?我集成了compositionalLayout吗?
下面是我代码:
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
}
}
谢谢你
编辑:更新的代码-
编辑:与WWDC中的Apple示例代码进行比较,我发现了此行为。
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
}
只有7个项目时,永远不会调用Scroll Delegate方法。
我仍然可以滚动,预期的行为应该是滚动代理方法在我有垂直反弹时被调用。
当有大约40个项目,但内容明显超出屏幕大小时,滚动代理确实会被调用。
有趣的是,现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
}
卷轴代理从来没有被调用。即使有40+项目。
关于如何强制UICollectionView与其ScrollViewDelegates进行通信,您有什么想法吗?
7条答案
按热度按时间kknvjkwl1#
答案是在截面(
NSCollectionLayoutSection
)上使用**visibleItemsInvalidationHandler
**闭包。每当事件产生动画时,此处理程序都会接收更新。它的操作类似于
scrollViewDidScroll
,并且在水平滚动组上,它将被传递所有项、滚动视图偏移量和NSCollectionLayoutEnvironment。https://developer.apple.com/documentation/uikit/nscollectionlayoutsection/3199096-visibleitemsinvalidationhandler
示例:
pu82cl6c2#
代码片段:
nwlqm0z13#
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。
只有垂直滚动组才会触发UIScrollViewDelegates。
不幸的是,这也意味着decelerationrate.fast似乎不能应用于水平滚动。它将被忽略。
重现问题和分析的步骤
通过在wwdc示例代码“集合视图布局中的改进”中实现UIScrollViewDelegate方法,可以重新创建此行为,如下所示:https://developer.apple.com/videos/play/wwdc2019/215/在类中:OrthogonalScrollBehaviorViewController.我们迅速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,则仍然需要具有嵌套CollectionViews和FlowLayout / Custom布局的传统方法。
备注
如果有人能指出我错过了什么,我会非常感激,直到那时,这将站在作为我的上述问题的答案。
感谢所有评论的人。
bt1cpqcv4#
如果垂直滚动collectionView,UICollectionViewDelegate将调用scrollDidView。在我的情况下,我试图从水平滚动跟踪,我使用以下代码来使事情工作。
这不是此问题的答案,但希望这对在collectionView组合布局中从水平滚动搜索跟踪当前显示单元格的人有所帮助
koaltpgm5#
我已经找到了一种处理此问题的简便方法,您可以避免设置正交滚动,而使用配置,方法如下:
这将调用
collectionview
的所有滚动代理。希望这对某些人有帮助。xzlaal3s6#
我试过用
但是这个方法在滚动时被多次调用,所以对我来说最好的解决方案是使用时间戳,并检查时间戳的差异,只有当它大于某个值,比如1或2,才调用这个动作。
kqhtkvqz7#
根据您的用例,还可以使用集合视图委托方法
在这些委托方法中,您可以在特定节将要显示单元格时做出React,以结束显示单元格