performbatchupdates

I am facing a nightmare of a crash during performBatchUpdates on a collection view . The problem is basically this: I have a lot of images on a directory on a server. I want to show the thumbnails of those files on a collection view . But the thumbnail have to be downloaded from the server asynchronously . As they arrive they will be inserted on the collection view using something like this: dispatch_async(dispatch_get_main_queue(), ^{ [self.collectionView performBatchUpdates:^{ if (removedIndexes && [removedIndexes count] > 0) { [self.collectionView deleteItemsAtIndexPaths:removedIndexes]; }