How to gracefully recover from an assertion failure in UICollectionView performBatchUpdates: - ios

Question

I have a UICollectionView that gets updated like so:
[self.collectionView performBatchUpdates:^{
[self.collectionView deleteItemsAtIndexPaths:pathsRemoved];
[self.collectionView insertItemsAtIndexPaths:pathsAdded];
}
Usually, this works just fine, but under certain circumstances the data source count doesn't match the original number of items - count of pathsRemoved + count of pathsAdded.
Therefore, I wrapped this code inside a #try/#catch block that then calls [self.collectionView reloadData].
What ends up happening, however, is that after reloading the data, the layout becomes messed up; cells that were previously there (above on-screen cells, but off screen) no longer show. The collection view's content size is correct, and I can scroll up an down, but only see the cells that were on screen at time of reload.
Interestingly, Reveal.app shows that the other cells do in fact exist, but are hidden; I have a hunch that this is a red herring, and that there is some view caching going on here, but the cells are nonetheless listed in Reveal.
I have tried invalidating the layout, calling layoutIfNeeded, as well as the various subclass-of-flow-layout tricks I've found, and nothing has fixed it.
I've resorted to mitigating the issue by doing my own benign assertion, and doing a check to make sure the counts add up. If they do, performBatchUpdates. Else, don't bother, and just reload. This works, since we're bypassing performBatchUpdates: altogether. But I have to ask:
Is there a better way to gracefully recover from an assertion exception thrown from within performBatchUpdates:? Or is it that UICollectionViews are just buggy (still, on iOS 7).

Answer 1

I just find a way to handle this !
I tried like you to wrap the performBatchUpdates: code inside a #try/#catch block that calls [collectionView reloadData].
Then I realized that the problems disappeared when my ViewController was deallocated, the collectionView also.
So I found the ugly solution (but working) : kill your old collectionView and create a new one in the catch block.
#try {
[collectionView performBatchUpdates:^ {
// Do your stuff
}];
}
#catch (NSException *exception) {
UIView *oldSuperview = self.collectionView.superview;
[self.collectionView removeFromSuperview];
self.collectionView = [[UICollectionView alloc] initWithFrame:self.collectionView.frame collectionViewLayout:self.collectionView.collectionViewLayout];
self.collectionView.dataSource = self;
self.collectionView.delegate = self;
// set other collectionView's properties here
[oldSuperview addSubview:self.collectionView];
}
I know this is bad, but it saved me !