Batch updates

[ArtSp]

When using custom UICollectionViewLayout for UICollectionView, it is possible that some cells have no layout attributes. When SectionedViewType inserts/moves cell at indexPath after datasource changed, cells without layout attributes being loaded and crash when func apply(_ layoutAttributes: UICollectionViewLayoutAttributes) was called.

Walk-around - Use subclassed collection view which will check if it can insert/move/delete cell :

class BatchUpdateSafeCollectionView: UICollectionView {
    
    override func insertItems(at indexPaths: [IndexPath]) {
        let safeIndexPaths = indexPaths.filter { collectionViewLayout.layoutAttributesForItem(at: $0) != nil }
        super.insertItems(at: safeIndexPaths)
    }
    
    override func deleteItems(at indexPaths: [IndexPath]) {
       ...
    }
    
    override func moveItem(at indexPath: IndexPath, to newIndexPath: IndexPath) {
        ...
    }
}

Solution is not perfect as collection view will ignore invalid batch updates (will use reloadData() instead) as number of inserted/deleted/moved items may not be equal.