插入到包含页脚的UICollectionView部分的问题(Issues inserting into UICollectionView section which contains a footer)

 我有一个典型的UICollectionView，它以垂直方式使用UICollectionViewFlowLayout。 我正在使用分页API来填充集合视图。 为了触发下一页下载，我在使用委托时要求页脚布局： 
 
- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath{
    RDLoadMoreReusableView *view = [collectionView dequeueReusableSupplementaryViewOfKind:kind withReuseIdentifier:@"RDLoadMoreReusableView" forIndexPath:indexPath];
    view.delegate = self;
    [view start];
    [self loadNextPageOfAssets];
    return view;
}
 
 这是我的loadNextPageOfAssets背后的代码： 
 
-(void)loadNextPageOfAssets{
    __weak RDRadiusGridViewController *weakSelf = self;

    // Increment page and request assets. They are added to cluster.assets before the completion block is called.
    self.cluster.pagination.page++;
    [self.cluster requestAssetsWithCompletionBlock:^(NSArray *assets) {

        SM_LOG_DEBUG(@"page.total: %ld assets.count: %ld", self.cluster.pagination.totalCount, (long)assets.count);

        NSMutableArray *indexPaths = [[NSMutableArray alloc]initWithCapacity:assets.count];
        for(NSUInteger index = 0; index < assets.count; index++){
            NSIndexPath *indexPath = [NSIndexPath indexPathForItem:self.cluster.assets.count - assets.count + index inSection:0];
            SM_LOG_DEBUG(@"Inserting indexPath: %ld:%ld", (long)indexPath.item, (long)indexPath.section);
            [indexPaths addObject:indexPath];
        }
        [weakSelf.collectionView performBatchUpdates:^{
            [weakSelf.collectionView insertItemsAtIndexPaths:indexPaths];
        } completion:^(BOOL finished) {

        }];

//            [weakSelf.collectionView reloadData];
    }];
}
 
 当我运行时，我可以去我的ViewController并看到加载的资产的第一页。 如果向下滚动，我会看到页脚视图（其中包含微调框），但是代码将在异常中断点处断开： 
 
[weakSelf.collectionView insertItemsAtIndexPaths:indexPaths];
 
 - [UICollectionViewData layoutAttributesForSupplementaryElementOfKind：atIndexPath：]，/SourceCache/UIKit/UIKit-3185.20/UICollectionViewData.m:829中的断言失败 
 
 
 然后，如果我继续它与错误崩溃： 
 
 2014-06-11 16：39：58.335 Radius-iOS [4901：525006] *由于未捕获异常'NSInternalInconsistencyException'，原因：'no UICollectionViewLayoutAttributes instance for -layoutAttributesForSupplementaryElementOfKind：UICollectionElementKindSectionFooter at path {length = 2，path = 0 - 0}'*第一次抛出调用堆栈： 
 
 
 这令我感到困惑。 layoutAttributesForSupplementaryElementOfKind听起来像是与布局类有关的事情，但我没有使用自定义流布局，而是使用默认提供的布局。 这听起来像苹果的代码是疯了，但我觉得我正确使用一切。 
 
 现在，如果我移动电话： 
 
[self loadNextPageOfAssets];
 
 从补充单元出列到UICollectionViewCell deque，并且一起删除页脚视图，然后插入工作很好。 
 
 现在我打电话reloadData而不是插入，但这是丑陋的。 
 
 我是否忽略了关于页脚的一些内容？ 

I've got a typical UICollectionView which is using UICollectionViewFlowLayout in a vertical fashion. I'm using a rest API with pagination to populate the collection view. In order to trigger the next page to download, I'm using the delegate when it asks for the footer layout:
 
- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath{
    RDLoadMoreReusableView *view = [collectionView dequeueReusableSupplementaryViewOfKind:kind withReuseIdentifier:@"RDLoadMoreReusableView" forIndexPath:indexPath];
    view.delegate = self;
    [view start];
    [self loadNextPageOfAssets];
    return view;
}
 
Here is the code behind my loadNextPageOfAssets:
 
-(void)loadNextPageOfAssets{
    __weak RDRadiusGridViewController *weakSelf = self;

    // Increment page and request assets. They are added to cluster.assets before the completion block is called.
    self.cluster.pagination.page++;
    [self.cluster requestAssetsWithCompletionBlock:^(NSArray *assets) {

        SM_LOG_DEBUG(@"page.total: %ld assets.count: %ld", self.cluster.pagination.totalCount, (long)assets.count);

        NSMutableArray *indexPaths = [[NSMutableArray alloc]initWithCapacity:assets.count];
        for(NSUInteger index = 0; index < assets.count; index++){
            NSIndexPath *indexPath = [NSIndexPath indexPathForItem:self.cluster.assets.count - assets.count + index inSection:0];
            SM_LOG_DEBUG(@"Inserting indexPath: %ld:%ld", (long)indexPath.item, (long)indexPath.section);
            [indexPaths addObject:indexPath];
        }
        [weakSelf.collectionView performBatchUpdates:^{
            [weakSelf.collectionView insertItemsAtIndexPaths:indexPaths];
        } completion:^(BOOL finished) {

        }];

//            [weakSelf.collectionView reloadData];
    }];
}
 
When I run I can go to my ViewController and see the first page of assets loaded. If I scroll down I'll see the footer view (which contains a spinner), but then the code will break at the exception break point at line:
 
[weakSelf.collectionView insertItemsAtIndexPaths:indexPaths];
 
Assertion failure in -[UICollectionViewData layoutAttributesForSupplementaryElementOfKind:atIndexPath:], /SourceCache/UIKit/UIKit-3185.20/UICollectionViewData.m:829
 
 
Then if I continue it crashes with the error:
 
2014-06-11 16:39:58.335 Radius-iOS[4901:525006] * Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'no UICollectionViewLayoutAttributes instance for -layoutAttributesForSupplementaryElementOfKind: UICollectionElementKindSectionFooter at path {length = 2, path = 0 - 0}' * First throw call stack:
 
 
This is puzzling to me. layoutAttributesForSupplementaryElementOfKind sounds like it's seomthing to do with the layout class, but I'm not using a custom flow layout rather the default one supplied. It sounds like Apple's code is mad but I feel that I'm using everything correctly. 
 
Now if I move the call:
 
[self loadNextPageOfAssets];
 
from the supplementary cell dequeue to teh UICollectionViewCell deque, and remove the footer views all together, then the insert works great. 
 
For now I'm calling reloadData instead of insert, but this is UGLY. 
 
Am I overlooking something about the footers?

原文：https://stackoverflow.com/questions/24174456