UICollectionView Assertion failure

Question

I m getting this error on performing insertItemsAtIndexPaths in UICollectionView

Assertion failure in:

-[UICollectionViewD         


        

Answer 1

It seems that the problem occurs when you either insert or move a cell to a section that contains a supplementary header or footer view (with UICollectionViewFlowLayout or a layout derived from that) and the section has a count of 0 cells before the insertion / move.

I could only circumvent the crash and still maintain the animations by having an empty and invisible cell in the section containing the supplementary header view like this:

1. Make - (NSInteger)collectionView:(UICollectionView *)view numberOfItemsInSection:(NSInteger)section return the actual cell `count + 1 for that section where the header view is.

2. In - (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath return

   if ((indexPath.section == YOUR_SECTION_WITH_THE_HEADER_VIEW) && (indexPath.item == [self collectionView:collectionView numberOfItemsInSection:indexPath.section] - 1)) {
           cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"EmptyCell" forIndexPath:indexPath];
   }
   

   ... an empty cell for that position. Remember to register the cell reuse in viewDidLoad or wherever you initialize your UICollectionView:

   [self.collectionView registerClass:[UICollectionReusableView class] forCellWithReuseIdentifier:@"EmptyCell"];
   

3. Use moveItemAtIndexPath: or insertItemsAtIndexPaths: without crashing.