在 iOS10.x 上重新排序项目时 UICollectionView 崩溃答案

【问题标题】：UICollectionView crashes when reordering items on iOS10.x在 iOS10.x 上重新排序项目时 UICollectionView 崩溃
【发布时间】：2018-04-11 09:53:28
【问题描述】：

我尝试根据本指南实现从 iOS10 开始呈现的内置 CollectionView 重新排序：http://nshint.io/blog/2015/07/16/uicollectionviews-now-have-easy-reordering/ 并且在 iOS11 上一切正常，但是在开始拖动 UICollectionView 中的任何项目（单元格）时在 iOS10 上崩溃

这是我的代码：

- (void)addCollectionViewGestureRecognizers
{
    if (!self.panGesture)
    {
        // gesture to drag and reorder tiles
        self.panGesture = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handleCollectionViewPanGesture:)];
            [self.collectionView addGestureRecognizer:self.panGesture];
    }
}

- (BOOL)collectionView:(UICollectionView *)collectionView canMoveItemAtIndexPath:(NSIndexPath *)indexPath
{
    return YES;
}

- (void)collectionView:(UICollectionView *)collectionView moveItemAtIndexPath:(NSIndexPath *)sourceIndexPath toIndexPath:(NSIndexPath *)destinationIndexPath
{
    CLog(@"Item moved from index path: %@ to index path: %@", sourceIndexPath, destinationIndexPath);
}

- (void)handleCollectionViewPanGesture:(UIPanGestureRecognizer *)gesture
{
    switch(gesture.state)
    {
        case UIGestureRecognizerStateBegan:
        {
            NSIndexPath *selectedIndexPath = [self.collectionView indexPathForItemAtPoint:[gesture locationInView:self.collectionView]];
            if(selectedIndexPath)
            {
                [self.collectionView beginInteractiveMovementForItemAtIndexPath:selectedIndexPath];
            }
            break;
        }
        case UIGestureRecognizerStateChanged:
        {
            [self.collectionView updateInteractiveMovementTargetPosition:[gesture locationInView:gesture.view]];
            break;
        }
        case UIGestureRecognizerStateEnded:
        {
            [self.collectionView endInteractiveMovement];
            break;
        }
        default:
        {
            [self.collectionView cancelInteractiveMovement];
            break;
        }
    }
}

和iOS 10每次上线都会崩溃：

[self.collectionView updateInteractiveMovementTargetPosition:[gesture locationInView:guesture.view]];

崩溃报告：

0   CoreFoundation                      0x0000000118f8bb0b __exceptionPreprocess + 171
1   libobjc.A.dylib                     0x0000000118961141 objc_exception_throw + 48
2   CoreFoundation                      0x0000000118ec0443 -[__NSArrayM insertObject:atIndex:] + 1603
3   UIKit                               0x00000001166f3577 -[UICollectionView _getOriginalReorderingIndexPaths:targetIndexPaths:] + 501
4   UIKit                               0x00000001166e2e50 -[UICollectionView _viewAnimationsForCurrentUpdate] + 7338
5   UIKit                               0x00000001166e7bf3 __71-[UICollectionView _updateWithItems:tentativelyForReordering:animator:]_block_invoke.2012 + 197
6   UIKit                               0x0000000115e4c08e +[UIView(Animation) performWithoutAnimation:] + 90
7   UIKit                               0x00000001166e682d -[UICollectionView _updateWithItems:tentativelyForReordering:animator:] + 3856
8   UIKit                               0x00000001166e0b33 -[UICollectionView _endItemAnimationsWithInvalidationContext:tentativelyForReordering:animator:] + 17030
9   UIKit                               0x00000001166e91cd -[UICollectionView _endUpdatesWithInvalidationContext:tentativelyForReordering:animator:] + 71
10  UIKit                               0x00000001166e9514 -[UICollectionView _performBatchUpdates:completion:invalidationContext:tentativelyForReordering:animator:] + 437
11  UIKit                               0x00000001166e933c -[UICollectionView _performBatchUpdates:completion:invalidationContext:tentativelyForReordering:] + 91
12  UIKit                               0x00000001166f09a3 -[UICollectionView _updateReorderingTargetPosition:forced:] + 1467
13  UIKit                               0x00000001166f122a -[UICollectionView updateInteractiveMovementTargetPosition:] + 29
14  myAPP                                 0x000000010dcb3b26 -[MenuCollectionViewController handleCollectionViewPanGesture:] + 710
15  UIKit                               0x00000001162c8f59 -[UIGestureRecognizerTarget _sendActionWithGestureRecognizer:] + 57
16  UIKit                               0x00000001162d0d57 _UIGestureRecognizerSendTargetActions + 109
17  UIKit                               0x00000001162ce70b _UIGestureRecognizerSendActions + 225

我忘了设置什么吗？

如果有人对此有任何想法，我将不胜感激......

【问题讨论】：

我认为应该是[self.collectionView updateInteractiveMovementTargetPosition:[gesture locationInView:gesture.view]]; 注意不是self.view 而是事实上gesture.view
@staticVoidMan，对不起，那是我的错。当我复制和粘贴代码时，我错误地将 guesture.view 更改为 self.view。原始代码是[gesture locationInView:gesture.view]，仅在iOS10上崩溃
@staticVoidMan，看来我找到了一个可以找到问题的地方。我有从 UICollectionViewFlowLayout 继承的自定义布局并覆盖其中的 targetIndexPathForInteractivelyMovingItem 函数。如果评论此覆盖，重新排序工作不会崩溃。只是项目移动到不正确的 indexPath
太棒了！您也应该将您的答案标记为已接受

标签： crash uicollectionview ios10.3

【解决方案1】：

好的，我似乎找到了崩溃的原因和可能的解决方案。我有从 UICollectionViewFlowLayout 继承的自定义布局并在其中覆盖函数 targetIndexPathForInteractivelyMovingItem。将项目移动到正确的位置。我是这样实现的：

- (NSIndexPath*)targetIndexPathForInteractivelyMovingItem:(NSIndexPath *)previousIndexPath withPosition:(CGPoint)position
{
    NSIndexPath *targetIndexPath = [self.collectionView indexPathForItemAtPoint:position];

    return targetIndexPath;
}

这在 iOS 11 上运行良好，但对于 iOS 10 indexPathForItemAtPoint 出于某种原因返回 nil（我不知道为什么）所以我不得不添加这个技巧来防止重新排序时崩溃

- (NSIndexPath*)targetIndexPathForInteractivelyMovingItem:(NSIndexPath *)previousIndexPath withPosition:(CGPoint)position
{
    NSIndexPath *targetIndexPath = [self.collectionView indexPathForItemAtPoint:position];

    if (!targetIndexPath) // on iOS10 indexpath can be nil by some reason
    {
        targetIndexPath = [NSIndexPath indexPathForRow:0 inSection:0];
    }

    return targetIndexPath;
}

【讨论】：