以前，我尝试用 UITableView 中的长按拖动来替换标准的 Apple 重新排序控件(从右侧的 handle 拖动单元格)。但是，由于某种原因，我无法通过长按拖动将单元格移动到已经没有单元格的部分。现在我正在尝试实现一个功能，用户可以在 UICollectionViewController 而不是 UITableView 的 2 个部分之间拖动单元格。我实现了长按拖动功能，但由于某种原因我遇到了同样的问题。我将如何向这些部分添加一个虚拟单元格，以便它们永远不会为空，或者是否有更好的方法来解决这个问题？是否还有一种无需长按即可拖动单元格的方法？

这些是我添加到我的 UICollectionViewController 类中以启用长按拖动的功能:

override func viewDidLoad() {
    super.viewDidLoad()

    let longPressGesture = UILongPressGestureRecognizer(target: self, action: "handleLongGesture:")
    self.collectionView!.addGestureRecognizer(longPressGesture)
}

func handleLongGesture(gesture: UILongPressGestureRecognizer) {

    switch(gesture.state) {

    case UIGestureRecognizerState.Began:
        guard let selectedIndexPath = self.collectionView!.indexPathForItemAtPoint(gesture.locationInView(self.collectionView)) else {
            break
        }
        collectionView!.beginInteractiveMovementForItemAtIndexPath(selectedIndexPath)
    case UIGestureRecognizerState.Changed:
        collectionView!.updateInteractiveMovementTargetPosition(gesture.locationInView(gesture.view!))
    case UIGestureRecognizerState.Ended:
        collectionView!.endInteractiveMovement()
    default:
        collectionView!.cancelInteractiveMovement()
    }
}

override func collectionView(collectionView: UICollectionView, moveItemAtIndexPath sourceIndexPath: NSIndexPath, toIndexPath destinationIndexPath: NSIndexPath) {

    let fromRow = sourceIndexPath.row
    let toRow = destinationIndexPath.row
    let fromSection = sourceIndexPath.section
    let toSection = destinationIndexPath.section

    var item: Item
    if fromSection == 0 {
        item = section1Items[fromRow]
        section1Items.removeAtIndex(fromRow)
    } else {
        item = section2Items[sourceIndexPath.row]
        section2Items.removeAtIndex(fromRow)
    }

    if toSection == 0 {
        section1Items.insert(score, atIndex: toRow)
    } else {
        section2Items.insert(score, atIndex: toRow)
    }
}

override func collectionView(collectionView: UICollectionView, canMoveItemAtIndexPath indexPath: NSIndexPath) -> Bool {
    return true
}

谢谢

最佳答案

要首先回答问题的第二部分，请使用 UIPanGestureRecogniser 而不是 UILongPressRecogniser。

对于空白部分，您可以向空白部分添加一个不可见的虚拟单元格。在 Storyboard中创建一个没有 subview 的原型(prototype)单元格，并确保它具有与 Collection View 相同的背景颜色。

如果该部分为空，您需要安排显示此单元格。但是您还需要在只有 1 个单元格的部分开始时添加一个虚拟单元格，否则该部分将在移动过程中折叠并且用户无法将单元格移回该部分从那里开始。

在手势处理程序中，开始移动时添加一个临时单元格。如果尚未移除单元格，则在拖动完成时也将其移除(如果单元格实际上并未移动，则不会调用委托(delegate) moveItemAtIndexPath 方法):

var temporaryDummyCellPath:NSIndexPath?

func handlePanGesture(gesture: UIPanGestureRecognizer) {

    switch(gesture.state) {
    case UIGestureRecognizerState.Began:
        guard let selectedIndexPath = self.collectionView.indexPathForItemAtPoint(gesture.locationInView(self.collectionView)) else {
            break
        }
        if model.numberOfPagesInSection(selectedIndexPath.section) == 1 {
            // temporarily add a dummy cell to this section
            temporaryDummyCellPath = NSIndexPath(forRow: 1, inSection: selectedIndexPath.section)
            collectionView.insertItemsAtIndexPaths([temporaryDummyCellPath!])
        }
        collectionView.beginInteractiveMovementForItemAtIndexPath(selectedIndexPath)
    case UIGestureRecognizerState.Changed:
        collectionView.updateInteractiveMovementTargetPosition(gesture.locationInView(gesture.view!))
    case UIGestureRecognizerState.Ended:
        collectionView.endInteractiveMovement()

        // remove dummy path if not already removed
        if let dummyPath = self.temporaryDummyCellPath {
            temporaryDummyCellPath = nil
            collectionView.deleteItemsAtIndexPaths([dummyPath])
        }

    default:
        collectionView.cancelInteractiveMovement()

        // remove dummy path if not already removed
        if let dummyPath = temporaryDummyCellPath {
            temporaryDummyCellPath = nil
            collectionView.deleteItemsAtIndexPaths([dummyPath])
        }
    }
}

在collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int)始终返回比模型中项目数多 1 的值，或者如果添加了临时虚拟单元格，则返回一个额外的单元格。

func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    // special case: about to move a cell out of a section with only 1 item
    // make sure to leave a dummy cell 
    if section == temporaryDummyCellPath?.section {
        return 2
    }

    // always keep one item in each section for the dummy cell
    return max(model.numberOfPagesInSection(section), 1)
}

在collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath)如果该行等于该部分模型中的项目数，则分配虚拟单元格。

禁止选择 collectionView(collectionView: UICollectionView, shouldSelectItemAtIndexPath indexPath: NSIndexPath) 中的单元格通过为虚拟单元格返回 false 而为其他单元格返回 true。

同样禁止移动 collectionView(collectionView: UICollectionView, canMoveItemAtIndexPath indexPath: NSIndexPath) 中的单元格

确保目标移动路径仅限于模型中的行:

func collectionView(collectionView: UICollectionView, targetIndexPathForMoveFromItemAtIndexPath originalIndexPath: NSIndexPath, toProposedIndexPath proposedIndexPath: NSIndexPath) -> NSIndexPath
{
    let proposedSection = proposedIndexPath.section
    if model.numberOfPagesInSection(proposedSection) == 0 {
        return NSIndexPath(forRow: 0, inSection: proposedSection)
    } else {
        return proposedIndexPath
    }

}

现在您需要处理最后一步。更新您的模型，然后根据需要添加或删除虚拟单元格:

func collectionView(collectionView: UICollectionView, moveItemAtIndexPath sourceIndexPath: NSIndexPath, toIndexPath destinationIndexPath: NSIndexPath)
{
    // move the page in the model
    model.movePage(sourceIndexPath.section, fromPage: sourceIndexPath.row, toSection: destinationIndexPath.section, toPage: destinationIndexPath.row)

    collectionView.performBatchUpdates({

        // if original section is left with no pages, add a dummy cell or keep already added dummy cell
        if self.model.numberOfPagesInSection(sourceIndexPath.section) == 0 {
            if self.temporaryDummyCellPath == nil {
                let dummyPath = NSIndexPath(forRow: 0, inSection: sourceIndexPath.section)
                collectionView.insertItemsAtIndexPaths([dummyPath])
            } else {
                // just keep the temporary dummy we already created
                self.temporaryDummyCellPath = nil
            }
        }

        // if new section previously had no pages remove the dummy cell
        if self.model.numberOfPagesInSection(destinationIndexPath.section) == 1 {
            let dummyPath = NSIndexPath(forRow: 0, inSection: destinationIndexPath.section)
            collectionView.deleteItemsAtIndexPaths([dummyPath])
        }
    }, completion: nil)

}

最后确保虚拟单元格没有辅助功能项，以便在打开画外音时跳过它。

关于ios - Swift:无法长按拖动单元格到 UICollectionViewController 和 UITableView 中的空白部分，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/35920874/