正文

　　功能

　　　　用 UICollectionView 实现两个 cell 之间的位置交互或者拖拽某个位置删除

　　问题

　　　　iOS 11 以上拖拽删除会崩溃，在 iOS 9、10 都没有问题

      错误

017-10-11 11:38:02.692004+0800 MOCR[2585:1047221] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'attempting to invalidate an item at an invalid indexPath: <NSIndexPath: 0x1c442a680> {length = 2, path = 0 - 1} globalIndex: 1 numItems: 1'
*** First throw call stack:
(0x181f3bd38 0x181450528 0x181f3bc0c 0x1828cac24 0x18be1091c 0x18bdd2ab8 0x18b4b74ac 0x18b4b48b8 0x18b569a4c 0x18bdd9e98 0x10275d49c 0x10275d45c 0x102762050 0x181ee3f20 0x181ee1afc 0x181e022d8 0x183c93f84 0x18b3af880 0x1009a753c 0x18192656c)
libc++abi.dylib: terminating with uncaught exception of type NSException

　　代码

func handleLongGesture(gesture: UILongPressGestureRecognizer) {

    switch(gesture.state) {

    case .began:
        guard let selectedIndexPath = self.collectionView.indexPathForItem(at: gesture.location(in: self.collectionView)) else {
            break
        }
        collectionView.beginInteractiveMovementForItem(at: selectedIndexPath)
    case .changed:
        collectionView.updateInteractiveMovementTargetPosition(gesture.location(in: gesture.view!))
    case .ended:
        self.collectionView.endInteractiveMovement()
        // 检测是否删除操作，是的话删除数据并调用 reloadData()
    default:
        collectionView.cancelInteractiveMovement()
    }
}

　　分析

　　　　测试发现调用 beginInteractiveMovementForItem 和 endInteractiveMovement 也会触发 reloadData 操作，这样删除前后会调用两次 reloadData，但是 reloadData 又是异步操作，所以就报错了。

　　解决

func handleLongGesture(gesture: UILongPressGestureRecognizer) {

    switch(gesture.state) {

    case .began:
        guard let selectedIndexPath = self.collectionView.indexPathForItem(at: gesture.location(in: self.collectionView)) else {
            break
        }
        collectionView.beginInteractiveMovementForItem(at: selectedIndexPath)
    case .changed:
        collectionView.updateInteractiveMovementTargetPosition(gesture.location(in: gesture.view!))
    case .ended:
        self.collectionView.endInteractiveMovement()
        DispatchQueue.main.asyncAfter(deadline: .now() + .milliseconds(300), execute: { [weak self] in
            // 检测是否删除操作，是的话删除数据并调用 reloadData()
        })
    default:
        collectionView.cancelInteractiveMovement()
    }
}

　　　　加一个延迟处理就行