ios - UICollectionViewDropDelegate 破坏了 UICollectionView 中的重新排序单元机制

Question

我正在尝试实现两个 collectionView，并在它们之间拖放单元格。但我在对 collectionView 内的单元格重新排序时遇到了奇怪的行为。这是复制该行为的最少代码。

提供的代码按预期工作，但后来我取消注释collectionView.dropDelegate = self它不再工作了。我试图找到 UICollectionViewDropDelegate 的哪个方法被调用，但没有一个被调用。

class ViewController: UIViewController, UICollectionViewDataSource, UICollectionViewDropDelegate {
    func collectionView(_ collectionView: UICollectionView, performDropWith coordinator: UICollectionViewDropCoordinator) {
        print("in drop")
    }

    @IBOutlet weak var collectionView: UICollectionView!
    var items = [UIColor.red, UIColor.green, UIColor.blue]
    override func viewDidLoad() {
        super.viewDidLoad()
//        collectionView.dropDelegate = self
    }

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return items.count
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath)
        cell.contentView.layer.backgroundColor = items[indexPath.item].cgColor
        return cell
    }

    func collectionView(_ collectionView: UICollectionView, canMoveItemAt indexPath: IndexPath) -> Bool {
        return true
    }

    func collectionView(_ collectionView: UICollectionView, moveItemAt sourceIndexPath: IndexPath, to destinationIndexPath: IndexPath) {
        let temp = items.remove(at: sourceIndexPath.item)
        items.insert(temp, at: destinationIndexPath.item)
    }

    @IBAction func handleLongGesture(_ gesture: UILongPressGestureRecognizer) {
        switch gesture.state {
        case .began:
            guard let selectedIndexPath = self.collectionView.indexPathForItem(at: gesture.location(in: self.collectionView)) else {
                break
            }
            self.collectionView.beginInteractiveMovementForItem(at: selectedIndexPath)
        case .changed:
            self.collectionView.updateInteractiveMovementTargetPosition(gesture.location(in: gesture.view!))
        case .ended:
            self.collectionView.endInteractiveMovement()
        default:
            self.collectionView.cancelInteractiveMovement()
        }
    }
}

example without dragDelegate

example with dragDelegate

所以这种情况发生了，我应该怎么做才能使用 dragDelegate 获得正常行为？

Answer 1

这有点难看，但我遇到了这个问题，我能找到的最简单的方法就是在调用手势识别器时禁用 dropDelegate。

@IBAction func handleLongGesture(_ gesture: UILongPressGestureRecognizer) {
    switch gesture.state {
    case .began:
        guard let selectedIndexPath = self.collectionView.indexPathForItem(at: gesture.location(in: self.collectionView)) else {
            break
        }
        self.collectionView.dropDelegate = nil // Drop delegate behaves VERY badly with beginInteractiveMovementForItem
        self.collectionView.beginInteractiveMovementForItem(at: selectedIndexPath)

    case .changed:
        self.collectionView.updateInteractiveMovementTargetPosition(gesture.location(in: gesture.view!))
    case .ended:
        self.collectionView.endInteractiveMovement()
        self.collectionView.dropDelegate = self
    default:
        self.collectionView.cancelInteractiveMovement()
        self.collectionView.dropDelegate = self
    }
}