按单元格分页 UICollectionView，而不是屏幕

Question

我有水平滚动的UICollectionView ，并且每个屏幕总是并排有 2 个单元格。 我需要滚动停止在单元格的开头。 启用分页后，集合视图会滚动整个页面，即一次 2 个单元格，然后停止。

我需要启用单个单元格滚动，或者在单元格边缘停止滚动多个单元格。

我试图UICollectionViewFlowLayout并实现方法targetContentOffsetForProposedContentOffset ，但到目前为止我只能打破我的集合视图并且它停止滚动。 有没有更简单的方法来实现这一点以及如何实现，或者我真的需要实现UICollectionViewFlowLayout子类的所有方法吗？ 谢谢。

Answer 1

好的，所以我在这里找到了解决方案： targetContentOffsetForProposedContentOffset:withScrollingVelocity 没有子类化 UICollectionViewFlowLayout

我应该在开始时搜索targetContentOffsetForProposedContentOffset 。

Answer 2

只需覆盖该方法：

- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset {
    *targetContentOffset = scrollView.contentOffset; // set acceleration to 0.0
    float pageWidth = (float)self.articlesCollectionView.bounds.size.width;
    int minSpace = 10;

    int cellToSwipe = (scrollView.contentOffset.x)/(pageWidth + minSpace) + 0.5; // cell width + min spacing for lines
    if (cellToSwipe < 0) {
        cellToSwipe = 0;
    } else if (cellToSwipe >= self.articles.count) {
        cellToSwipe = self.articles.count - 1;
    }
    [self.articlesCollectionView scrollToItemAtIndexPath:[NSIndexPath indexPathForRow:cellToSwipe inSection:0] atScrollPosition:UICollectionViewScrollPositionLeft animated:YES];
}

Answer 3

具有自定义页面宽度的水平分页（Swift 4 和 5）

这里介绍的许多解决方案会导致一些奇怪的行为，感觉不像是正确实现的分页。

---

但是， 本教程中提供的解决方案似乎没有任何问题。 感觉就像一个完美的分页算法。 您可以通过 5 个简单的步骤来实现它：

1. 将以下属性添加到您的类型： private var indexOfCellBeforeDragging = 0
2. 像这样设置collectionView delegate ： collectionView.delegate = self
3. 通过扩展添加对UICollectionViewDelegate一致性： extension YourType: UICollectionViewDelegate { }

4. 将以下方法添加到实现UICollectionViewDelegate一致性的扩展中，并为pageWidth设置一个值：

    func scrollViewWillBeginDragging(_ scrollView: UIScrollView) { let pageWidth = // The width your page should have (plus a possible margin) let proportionalOffset = collectionView.contentOffset.x / pageWidth indexOfCellBeforeDragging = Int(round(proportionalOffset)) }

5. 将以下方法添加到实现UICollectionViewDelegate一致性的扩展中，为pageWidth设置相同的值（您也可以将此值存储在中心位置）并为collectionViewItemCount设置一个值：

    func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) { // Stop scrolling targetContentOffset.pointee = scrollView.contentOffset // Calculate conditions let pageWidth = // The width your page should have (plus a possible margin) let collectionViewItemCount = // The number of items in this section let proportionalOffset = collectionView.contentOffset.x / pageWidth let indexOfMajorCell = Int(round(proportionalOffset)) let swipeVelocityThreshold: CGFloat = 0.5 let hasEnoughVelocityToSlideToTheNextCell = indexOfCellBeforeDragging + 1 < collectionViewItemCount && velocity.x > swipeVelocityThreshold let hasEnoughVelocityToSlideToThePreviousCell = indexOfCellBeforeDragging - 1 >= 0 && velocity.x < -swipeVelocityThreshold let majorCellIsTheCellBeforeDragging = indexOfMajorCell == indexOfCellBeforeDragging let didUseSwipeToSkipCell = majorCellIsTheCellBeforeDragging && (hasEnoughVelocityToSlideToTheNextCell || hasEnoughVelocityToSlideToThePreviousCell) if didUseSwipeToSkipCell { // Animate so that swipe is just continued let snapToIndex = indexOfCellBeforeDragging + (hasEnoughVelocityToSlideToTheNextCell ? 1 : -1) let toValue = pageWidth * CGFloat(snapToIndex) UIView.animate( withDuration: 0.3, delay: 0, usingSpringWithDamping: 1, initialSpringVelocity: velocity.x, options: .allowUserInteraction, animations: { scrollView.contentOffset = CGPoint(x: toValue, y: 0) scrollView.layoutIfNeeded() }, completion: nil ) } else { // Pop back (against velocity) let indexPath = IndexPath(row: indexOfMajorCell, section: 0) collectionView.scrollToItem(at: indexPath, at: .left, animated: true) } }

Answer 4

这是我在Swift 5 中实现的基于单元格的垂直分页：

override func targetContentOffset(forProposedContentOffset proposedContentOffset: CGPoint, withScrollingVelocity velocity: CGPoint) -> CGPoint {

    guard let collectionView = self.collectionView else {
        let latestOffset = super.targetContentOffset(forProposedContentOffset: proposedContentOffset, withScrollingVelocity: velocity)
        return latestOffset
    }

    // Page height used for estimating and calculating paging.
    let pageHeight = self.itemSize.height + self.minimumLineSpacing

    // Make an estimation of the current page position.
    let approximatePage = collectionView.contentOffset.y/pageHeight

    // Determine the current page based on velocity.
    let currentPage = velocity.y == 0 ? round(approximatePage) : (velocity.y < 0.0 ? floor(approximatePage) : ceil(approximatePage))

    // Create custom flickVelocity.
    let flickVelocity = velocity.y * 0.3

    // Check how many pages the user flicked, if <= 1 then flickedPages should return 0.
    let flickedPages = (abs(round(flickVelocity)) <= 1) ? 0 : round(flickVelocity)

    let newVerticalOffset = ((currentPage + flickedPages) * pageHeight) - collectionView.contentInset.top

    return CGPoint(x: proposedContentOffset.x, y: newVerticalOffset)
}

一些注意事项：

• 不会出现故障
• 将分页设置为假！ （否则这将不起作用）
• 允许您轻松设置自己的轻弹速度。
• 如果尝试此操作后仍然无法正常工作，请检查您的itemSize是否与项目的大小实际匹配，因为这通常是一个问题，尤其是在使用collectionView(_:layout:sizeForItemAt:) ，请改用带有 itemSize 的自定义变量。
• 这在您设置self.collectionView.decelerationRate = UIScrollView.DecelerationRate.fast时效果最佳。

这是一个横向版本（尚未彻底测试，因此请原谅任何错误）：

override func targetContentOffset(forProposedContentOffset proposedContentOffset: CGPoint, withScrollingVelocity velocity: CGPoint) -> CGPoint {

    guard let collectionView = self.collectionView else {
        let latestOffset = super.targetContentOffset(forProposedContentOffset: proposedContentOffset, withScrollingVelocity: velocity)
        return latestOffset
    }

    // Page width used for estimating and calculating paging.
    let pageWidth = self.itemSize.width + self.minimumInteritemSpacing

    // Make an estimation of the current page position.
    let approximatePage = collectionView.contentOffset.x/pageWidth

    // Determine the current page based on velocity.
    let currentPage = velocity.x == 0 ? round(approximatePage) : (velocity.x < 0.0 ? floor(approximatePage) : ceil(approximatePage))

    // Create custom flickVelocity.
    let flickVelocity = velocity.x * 0.3

    // Check how many pages the user flicked, if <= 1 then flickedPages should return 0.
    let flickedPages = (abs(round(flickVelocity)) <= 1) ? 0 : round(flickVelocity)

    // Calculate newHorizontalOffset.
    let newHorizontalOffset = ((currentPage + flickedPages) * pageWidth) - collectionView.contentInset.left

    return CGPoint(x: newHorizontalOffset, y: proposedContentOffset.y)
}

此代码基于我在个人项目中使用的代码，您可以在此处下载并运行 Example 目标来查看它。

Answer 5

这是我在Swift 4.2 中发现的用于水平滚动的最简单方法：

我在visibleCells上使用第一个单元格并滚动到然后，如果第一个可见单元格显示的宽度小于它的一半，我将滚动到下一个。

如果您的收藏垂直滚动，只需将x更改为y并将width更改为height

func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
    targetContentOffset.pointee = scrollView.contentOffset
    var indexes = self.collectionView.indexPathsForVisibleItems
    indexes.sort()
    var index = indexes.first!
    let cell = self.collectionView.cellForItem(at: index)!
    let position = self.collectionView.contentOffset.x - cell.frame.origin.x
    if position > cell.frame.size.width/2{
       index.row = index.row+1
    }
    self.collectionView.scrollToItem(at: index, at: .left, animated: true )
}

Answer 6

Evya 答案的 Swift 3 版本：

func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
  targetContentOffset.pointee = scrollView.contentOffset
    let pageWidth:Float = Float(self.view.bounds.width)
    let minSpace:Float = 10.0
    var cellToSwipe:Double = Double(Float((scrollView.contentOffset.x))/Float((pageWidth+minSpace))) + Double(0.5)
    if cellToSwipe < 0 {
        cellToSwipe = 0
    } else if cellToSwipe >= Double(self.articles.count) {
        cellToSwipe = Double(self.articles.count) - Double(1)
    }
    let indexPath:IndexPath = IndexPath(row: Int(cellToSwipe), section:0)
    self.collectionView.scrollToItem(at:indexPath, at: UICollectionViewScrollPosition.left, animated: true)


}

Answer 7

部分基于 StevenOjo 的回答。 我已经使用水平滚动和没有 Bounce UICollectionView 对此进行了测试。 cellSize 是 CollectionViewCell 大小。 您可以调整因子来修改滚动灵敏度。

override func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
    targetContentOffset.pointee = scrollView.contentOffset
    var factor: CGFloat = 0.5
    if velocity.x < 0 {
        factor = -factor
    }
    let indexPath = IndexPath(row: (scrollView.contentOffset.x/cellSize.width + factor).int, section: 0)
    collectionView?.scrollToItem(at: indexPath, at: .left, animated: true)
}

Answer 8

方法 1：集合视图

flowLayout是UICollectionViewFlowLayout属性

override func scrollViewWillEndDragging(scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {

    if let collectionView = collectionView {

        targetContentOffset.memory = scrollView.contentOffset
        let pageWidth = CGRectGetWidth(scrollView.frame) + flowLayout.minimumInteritemSpacing

        var assistanceOffset : CGFloat = pageWidth / 3.0

        if velocity.x < 0 {
            assistanceOffset = -assistanceOffset
        }

        let assistedScrollPosition = (scrollView.contentOffset.x + assistanceOffset) / pageWidth

        var targetIndex = Int(round(assistedScrollPosition))


        if targetIndex < 0 {
            targetIndex = 0
        }
        else if targetIndex >= collectionView.numberOfItemsInSection(0) {
            targetIndex = collectionView.numberOfItemsInSection(0) - 1
        }

        print("targetIndex = \(targetIndex)")

        let indexPath = NSIndexPath(forItem: targetIndex, inSection: 0)

        collectionView.scrollToItemAtIndexPath(indexPath, atScrollPosition: .Left, animated: true)
    }
}

方法 2：页面视图控制器

如果UIPageViewController满足您的要求，您可以使用它，每个页面都有一个单独的视图控制器。

Answer 9

这是执行此操作的直接方法。

案例很简单，但最终很常见（典型的缩略图滚动条具有固定的单元格大小和固定的单元格之间的间隙）

var itemCellSize: CGSize = <your cell size>
var itemCellsGap: CGFloat = <gap in between>

override func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
    let pageWidth = (itemCellSize.width + itemCellsGap)
    let itemIndex = (targetContentOffset.pointee.x) / pageWidth
    targetContentOffset.pointee.x = round(itemIndex) * pageWidth - (itemCellsGap / 2)
}

// CollectionViewFlowLayoutDelegate

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
    return itemCellSize
}

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAt section: Int) -> CGFloat {
    return itemCellsGap
}

请注意，没有理由调用 scrollToOffset 或深入布局。 本机滚动行为已经完成了一切。

干杯 :)

Answer 10

修改 Romulo BM answer 以进行速度聆听

func scrollViewWillEndDragging(
    _ scrollView: UIScrollView,
    withVelocity velocity: CGPoint,
    targetContentOffset: UnsafeMutablePointer<CGPoint>
) {
    targetContentOffset.pointee = scrollView.contentOffset
    var indexes = collection.indexPathsForVisibleItems
    indexes.sort()
    var index = indexes.first!
    if velocity.x > 0 {
       index.row += 1
    } else if velocity.x == 0 {
        let cell = self.collection.cellForItem(at: index)!
        let position = self.collection.contentOffset.x - cell.frame.origin.x
        if position > cell.frame.size.width / 2 {
           index.row += 1
        }
    }

    self.collection.scrollToItem(at: index, at: .centeredHorizontally, animated: true )
}

Answer 11

有点像 evya 的回答，但更流畅一点，因为它没有将 targetContentOffset 设置为零。

- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset {
    if ([scrollView isKindOfClass:[UICollectionView class]]) {
        UICollectionView* collectionView = (UICollectionView*)scrollView;
        if ([collectionView.collectionViewLayout isKindOfClass:[UICollectionViewFlowLayout class]]) {
            UICollectionViewFlowLayout* layout = (UICollectionViewFlowLayout*)collectionView.collectionViewLayout;

            CGFloat pageWidth = layout.itemSize.width + layout.minimumInteritemSpacing;
            CGFloat usualSideOverhang = (scrollView.bounds.size.width - pageWidth)/2.0;
            // k*pageWidth - usualSideOverhang = contentOffset for page at index k if k >= 1, 0 if k = 0
            // -> (contentOffset + usualSideOverhang)/pageWidth = k at page stops

            NSInteger targetPage = 0;
            CGFloat currentOffsetInPages = (scrollView.contentOffset.x + usualSideOverhang)/pageWidth;
            targetPage = velocity.x < 0 ? floor(currentOffsetInPages) : ceil(currentOffsetInPages);
            targetPage = MAX(0,MIN(self.projects.count - 1,targetPage));

            *targetContentOffset = CGPointMake(MAX(targetPage*pageWidth - usualSideOverhang,0), 0);
        }
    }
}

Answer 12

这是 Swift5 中的优化解决方案，包括处理错误的 indexPath。 - Michael Lin Liu

• 第1步。 获取当前单元格的 indexPath。
• 第2步。 检测滚动时的速度。
• 第三步。 当速度增加时增加 indexPath 的行。
• 第四步。 告诉集合视图滚动到下一个项目

    func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
        
        targetContentOffset.pointee = scrollView.contentOffset
        
        //M: Get the first visiable item's indexPath from visibaleItems.
        var indexPaths = *YOURCOLLECTIONVIEW*.indexPathsForVisibleItems
        indexPaths.sort()
        var indexPath = indexPaths.first!

        //M: Use the velocity to detect the paging control movement.
        //M: If the movement is forward, then increase the indexPath.
        if velocity.x > 0{
            indexPath.row += 1
            
            //M: If the movement is in the next section, which means the indexPath's row is out range. We set the indexPath to the first row of the next section.
            if indexPath.row == *YOURCOLLECTIONVIEW*.numberOfItems(inSection: indexPath.section){
                indexPath.row = 0
                indexPath.section += 1
            }
        }
        else{
            //M: If the movement is backward, the indexPath will be automatically changed to the first visiable item which is indexPath.row - 1. So there is no need to write the logic.
        }
        
        //M: Tell the collection view to scroll to the next item.
        *YOURCOLLECTIONVIEW*.scrollToItem(at: indexPath, at: .left, animated: true )
 }

Answer 13

这是我在 Swift 3 中的版本。计算滚动结束后的偏移量并使用动画调整偏移量。

collectionLayout是一个UICollectionViewFlowLayout()

func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
    let index = scrollView.contentOffset.x / collectionLayout.itemSize.width
    let fracPart = index.truncatingRemainder(dividingBy: 1)
    let item= Int(fracPart >= 0.5 ? ceil(index) : floor(index))

    let indexPath = IndexPath(item: item, section: 0)
    collectionView.scrollToItem(at: indexPath, at: .left, animated: true)
}

Answer 14

斯威夫特 5

我找到了一种无需继承 UICollectionView 的方法，只需计算水平的 contentOffset。 显然没有 isPagingEnabled 设置为真。 这是代码：

var offsetScroll1 : CGFloat = 0
var offsetScroll2 : CGFloat = 0
let flowLayout = UICollectionViewFlowLayout()
let screenSize : CGSize = UIScreen.main.bounds.size
var items = ["1", "2", "3", "4", "5"]

override func viewDidLoad() {
    super.viewDidLoad()
    flowLayout.scrollDirection = .horizontal
    flowLayout.minimumLineSpacing = 7
    let collectionView = UICollectionView(frame: CGRect(x: 0, y: 590, width: screenSize.width, height: 200), collectionViewLayout: flowLayout)
    collectionView.register(collectionViewCell1.self, forCellWithReuseIdentifier: cellReuseIdentifier)
    collectionView.delegate = self
    collectionView.dataSource = self
    collectionView.backgroundColor = UIColor.clear
    collectionView.showsHorizontalScrollIndicator = false
    self.view.addSubview(collectionView)
}

func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
    offsetScroll1 = offsetScroll2
}

func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) {
    offsetScroll1 = offsetScroll2
}

func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>){
    let indexOfMajorCell = self.desiredIndex()
    let indexPath = IndexPath(row: indexOfMajorCell, section: 0)
    flowLayout.collectionView!.scrollToItem(at: indexPath, at: .centeredHorizontally, animated: true)
    targetContentOffset.pointee = scrollView.contentOffset
}

private func desiredIndex() -> Int {
    var integerIndex = 0
    print(flowLayout.collectionView!.contentOffset.x)
    offsetScroll2 = flowLayout.collectionView!.contentOffset.x
    if offsetScroll2 > offsetScroll1 {
        integerIndex += 1
        let offset = flowLayout.collectionView!.contentOffset.x / screenSize.width
        integerIndex = Int(round(offset))
        if integerIndex < (items.count - 1) {
            integerIndex += 1
        }
    }
    if offsetScroll2 < offsetScroll1 {
        let offset = flowLayout.collectionView!.contentOffset.x / screenSize.width
        integerIndex = Int(offset.rounded(.towardZero))
    }
    let targetIndex = integerIndex
    return targetIndex
}

Answer 15

您也可以创建假滚动视图来处理滚动。

水平或垂直

// === Defaults ===
let bannerSize = CGSize(width: 280, height: 170)
let pageWidth: CGFloat = 290 // ^ + paging
let insetLeft: CGFloat = 20
let insetRight: CGFloat = 20
// ================

var pageScrollView: UIScrollView!

override func viewDidLoad() {
    super.viewDidLoad()

    // Create fake scrollview to properly handle paging
    pageScrollView = UIScrollView(frame: CGRect(origin: .zero, size: CGSize(width: pageWidth, height: 100)))
    pageScrollView.isPagingEnabled = true
    pageScrollView.alwaysBounceHorizontal = true
    pageScrollView.showsVerticalScrollIndicator = false
    pageScrollView.showsHorizontalScrollIndicator = false
    pageScrollView.delegate = self
    pageScrollView.isHidden = true
    view.insertSubview(pageScrollView, belowSubview: collectionView)

    // Set desired gesture recognizers to the collection view
    for gr in pageScrollView.gestureRecognizers! {
        collectionView.addGestureRecognizer(gr)
    }
}

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    if scrollView == pageScrollView {
        // Return scrolling back to the collection view
        collectionView.contentOffset.x = pageScrollView.contentOffset.x
    }
}

func refreshData() {
    ...

    refreshScroll()
}

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()

    refreshScroll()
}

/// Refresh fake scrolling view content size if content changes
func refreshScroll() {
    let w = collectionView.width - bannerSize.width - insetLeft - insetRight
    pageScrollView.contentSize = CGSize(width: pageWidth * CGFloat(banners.count) - w, height: 100)
}

Answer 16

这是我的解决方案，在 Swift 4.2 中，希望对您有所帮助。

class SomeViewController: UIViewController {

  private lazy var flowLayout: UICollectionViewFlowLayout = {
    let layout = UICollectionViewFlowLayout()
    layout.itemSize = CGSize(width: /* width */, height: /* height */)
    layout.minimumLineSpacing = // margin
    layout.minimumInteritemSpacing = 0.0
    layout.sectionInset = UIEdgeInsets(top: 0.0, left: /* margin */, bottom: 0.0, right: /* margin */)
    layout.scrollDirection = .horizontal
    return layout
  }()

  private lazy var collectionView: UICollectionView = {
    let collectionView = UICollectionView(frame: .zero, collectionViewLayout: flowLayout)
    collectionView.showsHorizontalScrollIndicator = false
    collectionView.dataSource = self
    collectionView.delegate = self
    // collectionView.register(SomeCell.self)
    return collectionView
  }()

  private var currentIndex: Int = 0
}

// MARK: - UIScrollViewDelegate

extension SomeViewController {
  func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
    guard scrollView == collectionView else { return }

    let pageWidth = flowLayout.itemSize.width + flowLayout.minimumLineSpacing
    currentIndex = Int(scrollView.contentOffset.x / pageWidth)
  }

  func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
    guard scrollView == collectionView else { return }

    let pageWidth = flowLayout.itemSize.width + flowLayout.minimumLineSpacing
    var targetIndex = Int(roundf(Float(targetContentOffset.pointee.x / pageWidth)))
    if targetIndex > currentIndex {
      targetIndex = currentIndex + 1
    } else if targetIndex < currentIndex {
      targetIndex = currentIndex - 1
    }
    let count = collectionView.numberOfItems(inSection: 0)
    targetIndex = max(min(targetIndex, count - 1), 0)
    print("targetIndex: \(targetIndex)")

    targetContentOffset.pointee = scrollView.contentOffset
    var offsetX: CGFloat = 0.0
    if targetIndex < count - 1 {
      offsetX = pageWidth * CGFloat(targetIndex)
    } else {
      offsetX = scrollView.contentSize.width - scrollView.width
    }
    collectionView.setContentOffset(CGPoint(x: offsetX, y: 0.0), animated: true)
  }
}

Answer 17

好的，所以建议的答案对我不起作用，因为我想按部分滚动，因此具有可变宽度的页面大小

我这样做了（仅限垂直）：

   var pagesSizes = [CGSize]()
   func scrollViewDidScroll(_ scrollView: UIScrollView) {
        defer {
            lastOffsetY = scrollView.contentOffset.y
        }
        if collectionView.isDecelerating {
            var currentPage = 0
            var currentPageBottom = CGFloat(0)
            for pagesSize in pagesSizes {
                currentPageBottom += pagesSize.height
                if currentPageBottom > collectionView!.contentOffset.y {
                    break
                }
                currentPage += 1
            }
            if collectionView.contentOffset.y > currentPageBottom - pagesSizes[currentPage].height, collectionView.contentOffset.y + collectionView.frame.height < currentPageBottom {
                return // 100% of view within bounds
            }
            if lastOffsetY < collectionView.contentOffset.y {
                if currentPage + 1 != pagesSizes.count {
                    collectionView.setContentOffset(CGPoint(x: 0, y: currentPageBottom), animated: true)
                }
            } else {
                collectionView.setContentOffset(CGPoint(x: 0, y: currentPageBottom - pagesSizes[currentPage].height), animated: true)
            }
        }
    }

在这种情况下，我使用节高度+页眉+页脚预先计算每个页面大小，并将其存储在数组中。 那是pagesSizes成员

Answer 18

我在这里创建了一个自定义集合视图布局，它支持：

• 一次分页一个单元格
• 根据滑动速度一次分页 2+ 个单元格
• 水平或垂直方向

这很简单：

let layout = PagingCollectionViewLayout()

layout.itemSize = 
layout.minimumLineSpacing = 
layout.scrollDirection = 

您可以将PagingCollectionViewLayout.swift添加到您的项目中

或者

将pod 'PagingCollectionViewLayout'添加到您的 podfile

Answer 19

final class PagingFlowLayout: UICollectionViewFlowLayout {
    private var currentIndex = 0

    override func targetContentOffset(forProposedContentOffset proposedContentOffset: CGPoint, withScrollingVelocity velocity: CGPoint) -> CGPoint {
        let count = collectionView!.numberOfItems(inSection: 0)
        let currentAttribute = layoutAttributesForItem(
            at: IndexPath(item: currentIndex, section: 0)
            ) ?? UICollectionViewLayoutAttributes()

        let direction = proposedContentOffset.x > currentAttribute.frame.minX
        if collectionView!.contentOffset.x + collectionView!.bounds.width < collectionView!.contentSize.width || currentIndex < count - 1 {
            currentIndex += direction ? 1 : -1
            currentIndex = max(min(currentIndex, count - 1), 0)
        }

        let indexPath = IndexPath(item: currentIndex, section: 0)
        let closestAttribute = layoutAttributesForItem(at: indexPath) ?? UICollectionViewLayoutAttributes()

        let centerOffset = collectionView!.bounds.size.width / 2
        return CGPoint(x: closestAttribute.center.x - centerOffset, y: 0)
    }
}

Answer 20

Олень Безрогий 的原始答案有问题，所以最后一个单元格集合视图滚动到开头

func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
    targetContentOffset.pointee = scrollView.contentOffset
    var indexes = yourCollectionView.indexPathsForVisibleItems
    indexes.sort()
    var index = indexes.first!
    // if velocity.x > 0 && (Get the number of items from your data) > index.row + 1 {
    if velocity.x > 0 && yourCollectionView.numberOfItems(inSection: 0) > index.row + 1 {
       index.row += 1
    } else if velocity.x == 0 {
        let cell = yourCollectionView.cellForItem(at: index)!
        let position = yourCollectionView.contentOffset.x - cell.frame.origin.x
        if position > cell.frame.size.width / 2 {
           index.row += 1
        }
    }
    
    yourCollectionView.scrollToItem(at: index, at: .centeredHorizontally, animated: true )
}

Answer 21

func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity 
velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
    targetContentOffset.pointee = scrollView.contentOffset
    var indexes = self.collectionHome.indexPathsForVisibleItems
    indexes.sort()
    var index = indexes.first!
    let cell = self.collectionHome.cellForItem(at: index)!
    let position = self.collectionHome.contentOffset.x - cell.frame.origin.x
    if position > cell.frame.size.width/2{
        index.row = index.row+1
    }
    self.collectionHome.scrollToItem(at: index, at: .left, animated: true )
}

Answer 22

这是我使用UICollectionViewFlowLayout覆盖targetContentOffset ：

（虽然最后，我最终没有使用它，而是使用 UIPageViewController。）

/**
 A UICollectionViewFlowLayout with...
 - paged horizontal scrolling
 - itemSize is the same as the collectionView bounds.size
 */
class PagedFlowLayout: UICollectionViewFlowLayout {

  override init() {
    super.init()
    self.scrollDirection = .horizontal
    self.minimumLineSpacing = 8 // line spacing is the horizontal spacing in horizontal scrollDirection
    self.minimumInteritemSpacing = 0
    if #available(iOS 11.0, *) {
      self.sectionInsetReference = .fromSafeArea // for iPhone X
    }
  }

  required init?(coder aDecoder: NSCoder) {
    fatalError("not implemented")
  }

  // Note: Setting `minimumInteritemSpacing` here will be too late. Don't do it here.
  override func prepare() {
    super.prepare()
    guard let collectionView = collectionView else { return }
    collectionView.decelerationRate = UIScrollViewDecelerationRateFast // mostly you want it fast!

    let insetedBounds = UIEdgeInsetsInsetRect(collectionView.bounds, self.sectionInset)
    self.itemSize = insetedBounds.size
  }

  // Table: Possible cases of targetContentOffset calculation
  // -------------------------
  // start |          |
  // near  | velocity | end
  // page  |          | page
  // -------------------------
  //   0   | forward  |  1
  //   0   | still    |  0
  //   0   | backward |  0
  //   1   | forward  |  1
  //   1   | still    |  1
  //   1   | backward |  0
  // -------------------------
  override func targetContentOffset( //swiftlint:disable:this cyclomatic_complexity
    forProposedContentOffset proposedContentOffset: CGPoint, withScrollingVelocity velocity: CGPoint) -> CGPoint {

    guard let collectionView = collectionView else { return proposedContentOffset }

    let pageWidth = itemSize.width + minimumLineSpacing
    let currentPage: CGFloat = collectionView.contentOffset.x / pageWidth
    let nearestPage: CGFloat = round(currentPage)
    let isNearPreviousPage = nearestPage < currentPage

    var pageDiff: CGFloat = 0
    let velocityThreshold: CGFloat = 0.5 // can customize this threshold
    if isNearPreviousPage {
      if velocity.x > velocityThreshold {
        pageDiff = 1
      }
    } else {
      if velocity.x < -velocityThreshold {
        pageDiff = -1
      }
    }

    let x = (nearestPage + pageDiff) * pageWidth
    let cappedX = max(0, x) // cap to avoid targeting beyond content
    //print("x:", x, "velocity:", velocity)
    return CGPoint(x: cappedX, y: proposedContentOffset.y)
  }

}

Answer 23

您可以使用以下库： https : //github.com/ink-spot/UPCarouselFlowLayout

这非常简单，而且您不需要考虑其他答案所包含的细节。