我UICollectionView使用水平滚动，并且在整个屏幕上始终并排有2个单元格。我需要滚动才能在单元格开始处停止。启用分页后，集合视图将滚动整个页面（一次是2个单元格），然后停止。

我需要启用单个单元格滚动，或者停止在单元格边缘的同时滚动多个单元格。

我试图子类化UICollectionViewFlowLayout并实现该方法targetContentOffsetForProposedContentOffset，但是到目前为止，我只能破坏我的收藏夹视图，并且它停止了滚动。有没有更简单的方法来实现这一目标以及如何实现，或者我真的需要实现所有UICollectionViewFlowLayout子类方法吗？谢谢。

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

我应该targetContentOffsetForProposedContentOffset在一开始就进行搜索。

只是重写方法：

- (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];
}

具有自定义页面宽度的水平分页（快速4和5）

这里介绍的许多解决方案会导致某些奇怪的行为，使您感觉好像没有正确实现分页。

但是，本教程中介绍的解决方案似乎没有任何问题。感觉就像是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. 设置collectionView delegate如下：collectionView.delegate = self
3. UICollectionViewDelegate通过扩展名添加一致性：extension YourType: UICollectionViewDelegate { }

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

   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，为设置相同的值pageWidth（也可以将此值存储在中心位置），并为设置一个值collectionViewItemCount：

   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)
       }
   }

Swift 3版本的Evya的答案：

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)


}

这是我发现在Swift 4.2中进行水平滚动的最简单方法：

我正在使用第一个单元格，visibleCells然后滚动到，如果第一个可见单元格显示的宽度小于一半，则滚动到下一个单元格。

如果您收藏滚动垂直，只需更改x通过y和width通过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 )
}

部分基于StevenOjo的回答。我已经使用水平滚动并且没有Bounce UICollectionView对其进行了测试。cellSize是CollectionViewCell的大小。您可以调整因子以修改滚动灵敏度。

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)
}

这是我在Swift 5中针对基于单元格的垂直分页的实现：

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：

• 不小故障
• 设置为假！（否则将无法正常工作）
• 使您可以轻松设置自己的轻弹速度。
• 如果尝试此操作后仍然itemSize无法解决问题，请检查您的尺寸是否与项目大小实际匹配，因为这通常是个问题，尤其是在使用时collectionView(_:layout:sizeForItemAt:)，请使用自定义变量来代替itemSize。
• 设置时效果最佳self.collectionView.decelerationRate = UIScrollView.DecelerationRate.fast。

这是水平版本（尚未进行全面测试，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)
}

该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，以进行检查。

方法1：集合视图

flowLayout是UICollectionViewFlowLayout财产

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

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

这是直接的方法。

情况很简单，但最终还是很普遍的（典型的缩略图滚动器具有固定的单元格大小和单元格之间的固定间隙）

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或进入布局。本机滚动行为已经可以完成所有操作。

欢呼全部：)

有点像evya的答案，但稍微平滑一点，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);
        }
    }
}

修改Romulo BM答案以进行速度监听

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 )
}

迅捷5

我找到了一种无需子类化UICollectionView的方法，只需在水平方向计算contentOffset即可。显然，没有将isPagingEnabled设置为true。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
}

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)
}

您也可以创建伪造的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)
}

好的，所以建议的答案对我不起作用，因为我想按部分滚动，因此页面宽度可变

我这样做（仅垂直）：

   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，我将使用部分高度+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

这是我的解决方案，希望在Swift 4.2中为您提供帮助。

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)
  }
}

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)
    }
}

ОленьБезрогий的原始答案有问题，因此在最后一个单元格收集视图上滚动到开头

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 )
}

这是我通过使用UICollectionViewFlowLayout来覆盖的方式targetContentOffset：

（尽管最后，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)
  }

}

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

这非常简单，并且您无需像其他答案一样考虑细节。

我在这里创建了一个自定义集合视图布局，该布局支持：

• 一次寻呼一个小区
• 一次滑动2个以上的单元，具体取决于滑动速度
• 水平或垂直方向

就像这样简单：

let layout = PagingCollectionViewLayout()

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

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

要么

添加pod 'PagingCollectionViewLayout'到您的Podfile