我正在构建一个自定义的布局集合视图.我的收藏中每个项目有2个补充视图.而当我想删除一个项目时,我的layoutAttributesForSupplementaryViewOfKind：atIndexPath：实现被调用与不再存在的补充视图.这意味着我得到一个索引路径,它不能正确地映射到我的数据源,并且我有一个超出限制的问题.
我做了一些日志记录,在第一个实例中是什么跟随,是当我们从一些数据开始时,或者当我们将一个项目插入到集合视图中时,集合视图被计算的正确和逻辑的方式.
第二组日志是当我删除一个对象从我的数据源deleteItemsAtIndexPaths：.
我的layoutAttributesForElementsInRect：看起来像这样：
- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
{
NSMutableArray* attributes = [NSMutableArray array];
for (NSInteger i = 0 ; i < [self.myData count]; i++) {
NSIndexPath *indexPath = [NSIndexPath indexPathForItem:i inSection:0];
NSLog(@"%@ indexPath.row:%d",NSStringFromSelector(_cmd),indexPath.row);
UICollectionViewLayoutAttributes *att = [self layoutAttributesForItemAtIndexPath:indexPath];
[attributes addObject:att];
UICollectionViewLayoutAttributes *att_supp = [self layoutAttributesForSupplementaryViewOfKind:@"one_kind" atIndexPath:indexPath];
[attributes addObject:att_supp];
UICollectionViewLayoutAttributes *linesAttr = [self layoutAttributesForSupplementaryViewOfKind:@"another_kind" atIndexPath:indexPath];
[attributes addObject:linesAttr];
}
return attributes;
}
初始日志(正确和逻辑)：
MyApp[18546:70b] layoutAttributesForElementsInRect: indexPath.row:0 MyApp[18546:70b] layoutAttributesForSupplementaryViewOfKind:atIndexPath: indexPath.row:0 MyApp[18546:70b] layoutAttributesForSupplementaryViewOfKind:atIndexPath: indexPath.row:0 MyApp[18546:70b] layoutAttributesForElementsInRect: indexPath.row:1 MyApp[18546:70b] layoutAttributesForSupplementaryViewOfKind:atIndexPath: indexPath.row:1 MyApp[18546:70b] layoutAttributesForSupplementaryViewOfKind:atIndexPath: indexPath.row:1 MyApp[18546:70b] layoutAttributesForElementsInRect: indexPath.row:2 MyApp[18546:70b] layoutAttributesForSupplementaryViewOfKind:atIndexPath: indexPath.row:2 MyApp[18546:70b] layoutAttributesForSupplementaryViewOfKind:atIndexPath: indexPath.row:2
删除项目后：
MyApp[18633:70b] layoutAttributesForElementsInRect: indexPath.row:0 MyApp[18633:70b] layoutAttributesForSupplementaryViewOfKind:atIndexPath: indexPath.row:0 MyApp[18633:70b] layoutAttributesForSupplementaryViewOfKind:atIndexPath: indexPath.row:0 MyApp[18633:70b] layoutAttributesForElementsInRect: indexPath.row:1 MyApp[18633:70b] layoutAttributesForSupplementaryViewOfKind:atIndexPath: indexPath.row:1 MyApp[18633:70b] layoutAttributesForSupplementaryViewOfKind:atIndexPath: indexPath.row:1 MyApp[18633:70b] layoutAttributesForSupplementaryViewOfKind:atIndexPath: indexPath.row:2
正如你可以看到layoutAttributesForSupplementaryViewOfKind：atIndexPath：被调用,但是绕过layoutAttributesForElementsInRect：
有谁知道会发生什么问题？
解决方法
我有同样的问题.我的布局为集合视图中的每个项目使用一个补充视图.我用几个步骤解决了这个问题.
首先,在 – prepareForCollectionViewUpdates :,我列举更新,并确定哪些项目正在消失.我缓存该组索引路径.
然后布局将调用 – indexPathsToDeleteForSupplementaryViewOfKind :.我刚从上面返回缓存的结果.
最后,在 – finalizeCollectionViewUpdates中,我清除缓存.我想这个步骤是可选的.
我也这样做了 – indexPathsToInsertForSupplementaryViewOfKind：为了一致性,尽管它没有它工作正常.
