将集合视图中的单元格移动到另一个部分的最后一个单元格之外不起作用

Question

为了能够 move/pan 集合视图中的单元格，应该实现 UIGestureRecognizer。这在单节集合视图中工作正常。但是，在多部分集合视图中，当一个单元格超出另一个部分的最后一个单元格 panned/moved 时，会发生错误。尽管“cellForItemAtIndexPath”在平移期间被正确触发以显示“新”单元格，但不应在平移超过最后一个可用单元格后触发它（即在这种情况下 indexPath.row == numberOfItemsInSection 并导致错误（参见下面的代码)).

在 table 视图中，（默认）moving/panning 实现不会出现此问题。

这可能是 Swift 中的错误吗？有没有人建议在平移超出部分最后一个单元格时避免触发“cellForItemAtIndexPath”？

下面是 Swift 2.3 中的工作代码示例，用于说明问题。

class CustomViewController: UIViewController, UICollectionViewDataSource, UICollectionViewDelegate, UICollectionViewDelegateFlowLayout {

    private var list = ["one", "two", "three","four","five","six","seven","eight"]
    private var itemsList: [[String]]!

    private var collectionView : UICollectionView!

    override func viewDidLoad() {
        super.viewDidLoad()

        itemsList = [list, list, list] // Create three sections

        collectionView = UICollectionView(frame: CGRectZero, collectionViewLayout: UICollectionViewFlowLayout())
        self.collectionView.dataSource = self
        self.collectionView.delegate = self
        self.collectionView.translatesAutoresizingMaskIntoConstraints = false
        self.collectionView.registerClass(CustomCell.self, forCellWithReuseIdentifier: "cell")

        let panGesture = UIPanGestureRecognizer(target: self, action: #selector(CustomViewController.handleGesture(_:)))
        self.collectionView.addGestureRecognizer(panGesture)
        self.view.addSubview(self.collectionView)
    }

    override func viewWillLayoutSubviews() {
        let margins = view.layoutMarginsGuide
        self.collectionView.leadingAnchor.constraintEqualToAnchor(margins.leadingAnchor, constant: 0).active = true
        self.collectionView.trailingAnchor.constraintEqualToAnchor(margins.trailingAnchor, constant: 0).active = true
        self.collectionView.bottomAnchor.constraintEqualToAnchor(view.bottomAnchor, constant: 0).active = true
        self.collectionView.topAnchor.constraintEqualToAnchor(view.topAnchor, constant: 0).active = true
    }

    override func viewWillAppear(animated: Bool) {
        super.viewWillAppear(animated)
    }

    func numberOfSectionsInCollectionView(collectionView: UICollectionView) -> Int   {
        return itemsList.count
    }

    func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
         return itemsList[section].count
    }

    func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCellWithReuseIdentifier("cell", forIndexPath: indexPath) as! CustomCell

        let items = itemsList[indexPath.section]

        cell.label.text = items[indexPath.row] // The error occurs here, after panning beyond the last cell of another section stating: "fatal error: Index out of range"
        return cell
    }

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

    func collectionView(collectionView: UICollectionView, moveItemAtIndexPath sourceIndexPath: NSIndexPath, toIndexPath destinationIndexPath: NSIndexPath) {
        let itemToMove = itemsList[sourceIndexPath.section][sourceIndexPath.row]
        itemsList[sourceIndexPath.section].removeAtIndex(sourceIndexPath.row)
        itemsList[destinationIndexPath.section].insert(itemToMove, atIndex: destinationIndexPath.row)
    }


    func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, referenceSizeForHeaderInSection section: Int) -> CGSize {
                  return CGSizeMake(collectionView.bounds.size.width, 50)
    }

    func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize {
        return CGSizeMake(collectionView.bounds.size.width, 40)
    }

    func handleGesture(gesture: UIPanGestureRecognizer) {
        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()
        }
    }
}


class CustomCell: UICollectionViewCell {
    var label: UILabel!
    required init(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)!
    }

    override init(frame: CGRect) {
        super.init(frame: frame)
        self.backgroundColor = UIColor.whiteColor()
        self.label = UILabel()
        self.label.translatesAutoresizingMaskIntoConstraints = false
        self.contentView.addSubview(self.label)
    }

    override func layoutSubviews() {
        super.layoutSubviews()
        let margins = self.contentView.layoutMarginsGuide
        self.label.leadingAnchor.constraintEqualToAnchor(margins.leadingAnchor).active = true
        self.label.trailingAnchor.constraintEqualToAnchor(margins.trailingAnchor).active = true
        self.label.centerYAnchor.constraintEqualToAnchor(self.contentView.centerYAnchor).active = true
    }
}

Answer 1

根据 Apple 的说法，我的问题中描述的问题是 iOS 中的一个错误，似乎在 iOS 10 beta (xcode 8 GM) 的当前版本中已解决。

遗憾的是，集合视图的其他问题尚未解决，例如基本支持将项目移动到空白部分。

将集合视图中的单元格移动到另一个部分的最后一个单元格之外不起作用

Moving a cell in a collection view beyond the last cell of another section does not work

uigesturerecognizer

ios

uicollectionview