scrollToItem forces crash in case of index out of range

[adomanski]

The method scrollToItem validates the index and forces crash if the index is out of range of already built items. This looks correct but one notice: when we call scrollToItem we cannot be sure that index is correct because we have no way to verify its value. So could you please:

1. add logic to bypass crash (or create new method which don't produce crash or add new parameter, etc.)
2. or make accessible numberOfItems value

Thanks a lot for your awesome library

[ls19491314]

I had the same problem, and I could try this if I only had one section pagerView.scrollToItem(at: index, animated: true)

[r00li]

I am having the same issue myself. I am trying to reload the pager view data and then scroll to an item after a delay like this:

        self.pagerView.reloadData()

        DispatchQueue.main.async {
            // A trick how we can wait for the collection view to finish the reload

            if parentCard.currentItemIndex < ((parentCard.data as? DailyPlanFeedGalleryDisplayable)?.imageItems.count ?? 0) {
                self.pagerView.scrollToItem(at: parentCard.currentItemIndex, animated: false)
            }
        }

This works most of the time, but sometimes for some reason this fails and the pagerView crashes. We either need a way to verify the index ourselves or this needs to fail safely.

[dingronghui]

Just do this:

self.pagerView.layoutIfNeeded()
self.pagerView.reloadData()
self.pagerView.scrollToItem(at: index, animated: true)

[benatautolist]

+1 on this, a lot of folks are getting this crash (numerous other issues) we at a minimum need read access to numberOfItems so we can make this fail safely.

Update: After doing some more digging I found that UICollectionView#reloadData will update numberOfItems immediately if you call layoutIfNeeded afterwards. You should also make sure to call reloadData and scrollToItem on the main thread. Unfortunately, it's not a great fix for all cases considering the potential performance impact.

[kennic]

forcing a fatalError on scrollToItem is a very bad idea, please remove that line. If the app scroll to a out-of-index item, just scroll to the maximum index (or do nothing if empty item) instead.

[superno02]

let numberOfItems = self.dataSource?.numberOfItems(in: self) ?? 0