-layoutAttributesForSupplementaryElementOfKind没有UICollectionViewLayoutAttributes实例： [英] no UICollectionViewLayoutAttributes instance for -layoutAttributesForSupplementaryElementOfKind:

问题描述

标题是我得到的错误，我不知道为什么，但这里有一些信息，所以希望有人在这里可以解释我。

The title is the error I'm getting and I have no idea why, but here is some information so hopefully someone on here can elucidate me.

我有子类 UICollectionViewFlowLayout 因为这可以节省我在 prepareLayout 中计算单元格的帧（也许这是一个问题？）。然后我使用 UICollectionViewLayoutAttributes 信息来计算一个补充视图，我得到了我想要的布局。

I have subclassed UICollectionViewFlowLayout as this saves me calculating the frames for the cell's myself (perhaps this is an issue?) in prepareLayout. I then use the UICollectionViewLayoutAttributes information to calculate a supplementary view that over lays it, I get the layout I desire.

我使用 performBatchUpdates：completion：来添加，删除和更新视图。插入工作正常，但删除项目是出现标题中显示的错误。

I use performBatchUpdates:completion: to add,remove and update the view. Insertion works fine, however deleting items is when the error shown in the title appears.

所以我知道为什么错误发生但我不知道为什么它甚至应该发生。通过一个导致问题的场景的示例来澄清

So I know why the error is happening but i don't know why it should even be happening. To clarify with an example going through a scenario that causes the issue

1. 从1个项目开始，包含1个补充视图1个部分


2. 再添加两个项目（ prepareLayout 查看包含3个补充视图的3个项目）


3. 删除项目（ prepareLayout 看到2个视图，带有2个补充视图）


4. layoutAttributesForSupplementaryViewOfKind：atIndexPath：被调用询问对于部分的索引路径的属性：0和项目：2


5. 崩溃，因为它要求第三个补充视图的属性，即使它之前称为准备布局设置最多2个项目和2个补充意见


6. 举手辞职和绝望

1. Start with 1 item with 1 supplementary view 1 section
2. Add two more items (prepareLayout sees 3 items with 3 supplementary views)
3. Delete item (prepareLayout sees 2 views with 2 supplementary views)
4. layoutAttributesForSupplementaryViewOfKind:atIndexPath: is called asking for attributes for index path with section:0 and item:2
5. Crash because it asked for attributes for a third supplementary view even though earlier it called prepare layout setting up 2 items and 2 supplementary views
6. Throw hands up in resignation and despair

所以据我所知，违规函数是：

so the offending function as far as i can tell is:

- (UICollectionViewLayoutAttributes *)layoutAttributesForSupplementaryViewOfKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)indexPath
{
    return self.layoutInfo[elementKind][indexPath];
}

这当然是由 UICollectionView 所以我不知道为什么它要求在索引路径上的补充视图。

which of course is called automagically by the internal networking of UICollectionView so I have no clue as to why it's asking for that supplementary view at that index path.

任何人都有任何想法？也许这就是我如何使用 performBatchUpdates：completion：但删除工作正常，直到添加补充视图。我可以根据需要提供更多的代码/解释。

Anyone got any ideas? Perhaps it's how i use performBatchUpdates:completion: but deletion worked fine until adding supplementary views. I can provide more code/explanation as necessary.

推荐答案

我搜索论坛寻找答案并找到了一些建议。他们都没有给我我需要的救援，最终为了满足最后期限，我完全放弃了补充意见的使用。

I scoured the forums looking for an answer and came across a few suggestions. None of them gave me the succour I needed, and eventually in the interest of meeting deadlines, I dropped the use of supplementary views altogether.

几个星期后出于好奇我再次环顾四周，最终发现了以下帖子，现在我又回到了再次使用补充意见。

A few weeks later out of curiosity I looked around again and eventually came across the following post and now I'm back to using supplementary views again.

所以，不要忘记退回你的：

So, don't forget to return your:

- (NSArray<NSIndexPath *> *)indexPathsToDeleteForSupplementaryViewOfKind:(NSString *)elementKind
{
    return self.removedIndexPaths;
}

到您的收藏夹视图布局。

to your collection view layout.

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