UICollectionView insertItemsAtIndexPaths Throws

Question

我在UICollectionView上遇到了自定义布局对象的问题。插入项时，将引发NSInternalInconsistencyException：

2012年-11-16 10:01:18.920 MyApp4520:430 b * -NSIndexPath行断言失败，-NSIndexPath 2012-11-16 10:01:18.924 MyApp4520:430 b终止应用程序，原因是：“与UITableView一起使用的无效索引路径”。传递给表视图的索引路径必须包含两个指定节和行的索引。如果可能，请在UITableView.h中使用NSIndexPath上的类别。**第一次抛出调用堆栈：(0x370282a3 0x33eb097f 0x3702815d 0x347d72af 0x338c29bb 0x33cb8e1f 0x33ca95db 0x9cff9 0x33ca44b5 0x33ca4295 0x332990x9a9 0xa9 0xa554f 0x797539 0x3478edb9 0x3480db 0x60cb11f 0x60cf6x63x3facc1 36dd3x11 36ddx0x4 libc++abi.dylib)，称为抛出异常。

下面是启动插入的代码：

GetItemsRequest *request = [[GetItemsRequest alloc] init];
self.activeConnection = [[ServiceConnection alloc] initWithRequest:request
                                                        completion:^(GetItemsResponse *response, NSError *error) {

                                                            [self.collectionView performBatchUpdates:^{
                                                                [self.items addObjectsFromArray:response.items];
                                                                NSMutableArray *newIndexPaths = [NSMutableArray array];
                                                                for (Item *item in response.items)
                                                                {
                                                                    [newIndexPaths addObject:[NSIndexPath indexPathForItem:[self.items indexOfObject:item]
                                                                                                                 inSection:0]];
                                                                }
                                                                [self.collectionView insertItemsAtIndexPaths:newIndexPaths];
                                                            } completion:NULL];                                                                
                                                            [self.pullRefreshView refreshLastUpdatedDate];
                                                            [self.pullRefreshView scrollViewDataSourceDidFinishedLoading:self.collectionView];
                                                            self.activeConnection = nil;
                                                        }];
[self.activeConnection start];

如果我将自定义布局对象替换为UICollectionViewFlowLayout对象，则此代码可以工作，因此我认为它是正确的。如果我只调用[self.collectionView reloadData]，定制布局就能工作，所以布局对象处理插入的方式肯定有问题。

崩溃发生在对super的调用中。

- (void)prepareForCollectionViewUpdates:(NSArray *)updateItems
{
    [super prepareForCollectionViewUpdates:updateItems];

    for (UICollectionViewUpdateItem *item in updateItems)
    {
        if (item.updateAction == UICollectionUpdateActionDelete)
        {
            _items--;
        }
        else if (item.updateAction == UICollectionUpdateActionInsert)
        {
            _items++;
        }
    }
    _rows = -1;
}

然而，当我打印updateItems的描述时，实际上所有的索引路径都有两个索引：

<__NSArrayM 0x1f06af20>( <UICollectionViewUpdateItem: 0x1ddc2360> index path before update ((null)) index path after update (<NSIndexPath 0x1ddc1eb0> 2 indexes [0, 0]) action (insert), <UICollectionViewUpdateItem: 0x1ddc23d0> index path before update ((null)) index path after update (<NSIndexPath 0x1ddc1f00> 2 indexes [0, 1]) action (insert), <UICollectionViewUpdateItem: 0x1ddc23f0> index path before update ((null)) index path after update (<NSIndexPath 0x1ddc1f20> 2 indexes [0, 2]) action (insert), <UICollectionViewUpdateItem: 0x1ddc2410> index path before update ((null)) index path after update (<NSIndexPath 0x1ddc1f50> 2 indexes [0, 3]) action (insert), <UICollectionViewUpdateItem: 0x1ddc2430> index path before update ((null)) index path after update (<NSIndexPath 0x1ddc1f80> 2 indexes [0, 4]) action (insert), <UICollectionViewUpdateItem: 0x1ddc2470> index path before update ((null)) index path after update (<NSIndexPath 0x1ddc1e00> 2 indexes [0, 5]) action (insert), <UICollectionViewUpdateItem: 0x1ddc2490> index path before update ((null)) index path after update (<NSIndexPath 0x1ddc1e20> 2 indexes [0, 6]) action (insert), <UICollectionViewUpdateItem: 0x1ddc24b0> index path before update ((null)) index path after update (<NSIndexPath 0x1ddc1fe0> 2 indexes [0, 7]) action (insert), <UICollectionViewUpdateItem: 0x1ddc24d0> index path before update ((null)) index path after update (<NSIndexPath 0x1ddc2010> 2 indexes [0, 8]) action (insert), <UICollectionViewUpdateItem: 0x1ddc2450> index path before update ((null)) index path after update (<NSIndexPath 0x1ddc1fb0> 2 indexes [0, 9]) action (insert), <UICollectionViewUpdateItem: 0x1ddc2530> index path before update ((null)) index path after update (<NSIndexPath 0x1ddc2090> 2 indexes [0, 10]) action (insert), <UICollectionViewUpdateItem: 0x1ddc2550> index path before update ((null)) index path after update (<NSIndexPath 0x1ddc20c0> 2 indexes [0, 11]) action (insert), <UICollectionViewUpdateItem: 0x1ddc2570> index path before update ((null)) index path after update (<NSIndexPath 0x1ddc20f0> 2 indexes [0, 12]) action (insert), <UICollectionViewUpdateItem: 0x1ddc2590> index path before update ((null)) index path after update (<NSIndexPath 0x1ddc2120> 2 indexes [0, 13]) action (insert), <UICollectionViewUpdateItem: 0x1ddc25b0> index path before update ((null)) index path after update (<NSIndexPath 0x1ddc2150> 2 indexes [0, 14]) action (insert), <UICollectionViewUpdateItem: 0x1ddc25d0> index path before update ((null)) index path after update (<NSIndexPath 0x1ddc2180> 2 indexes [0, 15]) action (insert), <UICollectionViewUpdateItem: 0x1ddc25f0> index path before update ((null)) index path after update (<NSIndexPath 0x1ddc21b0> 2 indexes [0, 16]) action (insert), <UICollectionViewUpdateItem: 0x1ddc2680> index path before update ((null)) index path after update (<NSIndexPath 0x1ddc2250> 2 indexes [0, 17]) action (insert), <UICollectionViewUpdateItem: 0x1ddc26a0> index path before update ((null)) index path after update (<NSIndexPath 0x1ddc2280> 2 indexes [0, 18]) action (insert), <UICollectionViewUpdateItem: 0x1ddc26c0> index path before update ((null)) index path after update (<NSIndexPath 0x1ddc22b0> 2 indexes [0, 19]) action (insert) )

那么，为什么这段代码会抛出一个异常，说明确实需要两个索引？任何帮助都是非常感谢的。

Answer 1

明白了。在为标题创建布局属性时，我使用了[NSIndexPath indexPathWithIndex:]。因为布局对象决定了补充视图的索引路径意味着什么，我想我只需要一个索引就可以了。显然不是。