ios - 将 Collection View 中的单元格移动到另一部分的最后一个单元格之外不起作用
<p><p>为了能够在 Collection View 中移动/平移单元格，应该实现 UIGestureRecognizer。这在单节 Collection View 中工作正常。但是，在多节 Collection View 中，当一个单元格被平移/移动到另一个节的最后一个单元格之外时，会发生错误。
尽管“cellForItemAtIndexPath”在平移期间被正确触发以显示"new"单元格，但不应在平移超出最后一个可用单元格后触发(即在这种情况下 indexPath.row == numberOfItemsInSection 并导致错误(参见下面的代码)) .</p>
<p>在表格 View 中，(默认)移动/平移实现不会出现此问题。</p>
<p>这可能是 Swift 中的一个错误吗？是否有人建议在平移超出部分中的最后一个单元格时避免触发“cellForItemAtIndexPath”？ </p>
<p>下面是 Swift 2.3 中的一个工作代码示例来说明问题。</p>
<pre><code>class CustomViewController: UIViewController, UICollectionViewDataSource, UICollectionViewDelegate, UICollectionViewDelegateFlowLayout {
private var list = ["one", "two", "three","four","five","six","seven","eight"]
private var itemsList: []!
private var collectionView : UICollectionView!
override func viewDidLoad() {
super.viewDidLoad()
itemsList = // 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.count
}
func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCellWithReuseIdentifier("cell", forIndexPath: indexPath) as! CustomCell
let items = itemsList
cell.label.text = items // 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
itemsList.removeAtIndex(sourceIndexPath.row)
itemsList.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
}
}
</code></pre></p>
<br><hr><h1><strong>Best Answer-推荐答案</ strong></h1><br>
<p><p>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。</p>
<p>不幸的是， Collection View 的其他问题尚未修复，例如将项目移动到空白部分的基本支持。 </p></p>
<p style="font-size: 20px;">关于ios - 将 Collection View 中的单元格移动到另一部分的最后一个单元格之外不起作用，我们在Stack Overflow上找到一个类似的问题：
<a href="https://stackoverflow.com/questions/39318624/" rel="noreferrer noopener nofollow" style="color: red;">
https://stackoverflow.com/questions/39318624/
</a>
</p>
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