Question

为了能够在集合视图中移动/平移单元格，应该实现UIGestureRecognizer。这在单节集合视图中工作正常。但是，在多节集合视图中，当单元格被平移/移动到另一个节的最后一个单元格之外时会发生错误。虽然“panForItemAtIndexPath”被正确触发以在平移期间显示“新”单元格，但是在平移超出最后一个可用单元格之后不应该触发它（即在那种情况下indexPath.row == numberOfItemsInSection并导致错误（参见下面的代码））

在表格视图中，（默认）移动/平移实现不会发生此问题。

这可能是Swift中的一个错误吗？是否有人建议在平移超出节中最后一个单元格的过程中避免触发“cellForItemAtIndexPath”？

以下是Swift 2.3中的一个工作代码示例来说明问题。

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，并且似乎在当前版本的iOS 10 beta（xcode 8 GM）中得到了解决。

不幸的是，集合视图的其他问题尚未解决，例如将项目移动到空白部分的基本支持。

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

1 个答案: