-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，希望这里的人可以解释我.

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.

我已将 UICollectionViewFlowLayout 子类化，因为这样可以节省我自己在 prepareLayout 中计算单元格的帧(也许这是一个问题?).然后我使用 UICollectionViewLayoutAttributes 信息来计算覆盖它的补充视图，得到我想要的布局.

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，但删除项目时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.

所以我知道为什么会发生错误，但我不知道为什么会发生.举例说明导致问题的场景

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 个项目和 1 个补充视图 1 个部分开始
2. 再添加两个项目(prepareLayout 看到 3 个项目和 3 个补充视图)
3. 删除项目(prepareLayout 看到 2 个视图和 2 个补充视图)
4. layoutAttributesForSupplementaryViewOfKind:atIndexPath: 被称为请求索引路径的属性 section:0 和 item:2
5. 崩溃，因为它要求第三个补充视图的属性，即使之前它调用了准备布局设置 2 个项目和 2 个补充视图
6. 在无奈和绝望中举手

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，有问题的功能是:

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 的内部网络自动调用的，所以我不知道它为什么在该索引路径上要求该补充视图.

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.

有人有什么想法吗?也许这就是我使用 performBatchUpdates:completion: 的方式，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

我搜索了论坛寻找答案并遇到了一些建议.他们都没有给我我需要的帮助，最终为了赶上最后期限，我完全放弃了使用补充意见.

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.

几周后，出于好奇，我再次环顾四周，最终看到了以下帖子 现在我又开始使用补充视图了.

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，别忘了返回您的:

So, don't forget to return your:

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

到您的集合视图布局.

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