Scroll to bottom as new content comes in - ios

Question

So I have a UICollectionView that sort of houses a chat function in my app. As users send new messages they are brought in to the app via an observer pattern. However when new content comes in. It ends up below the keyboard and never adjust itself up. When I toggle the keyboard I have a function like this which seems to accomplish this goal. However, when I try similar code in my completion handler it fails and gives me this message.
'NSInvalidArgumentException', reason: 'attempt to scroll to invalid index path: {length = 2, path = 0 - 9}'
*** First throw call stack:
fileprivate func tryObserveComments(){
print(eventKey)
commentHandle = ChatService.observeMessages(forChatKey: eventKey) { (ref, newComments) in
self.commentRer = ref
self.comments.append(newComments!)
self.adapter.performUpdates(animated: true)
let item = self.collectionView.numberOfItems(inSection: self.collectionView.numberOfSections - 1) - 1
let insertionIndexPath = IndexPath(item: item, section: self.collectionView.numberOfSections - 1)
self.collectionView.scrollToItem(at: insertionIndexPath, at: UICollectionViewScrollPosition.top, animated: true)
}
}
Also for some reason in the strange instance that it does work. Some of the keyboard is partially covering the cell

Answer 1

Try it using performBatchUpdates, i think it will work as you excepted
fileprivate func tryObserveComments(){
print(eventKey)
commentHandle = ChatService.observeMessages(forChatKey: eventKey) { (ref, newComments) in
self.commentRer = ref
self.comments.append(newComments!)
self.adapter.performUpdates(animated: true)
self.collectionView.performBatchUpdates({
let item = self.collectionView.numberOfItems(inSection: self.collectionView.numberOfSections - 1) - 1
let insertionIndexPath = IndexPath(item: item, section: self.collectionView.numberOfSections - 1)
}, completion: { (Bool) in
self.collectionView.scrollToItem(at: insertionIndexPath, at: UICollectionViewScrollPosition.top, animated: true)
})
}
}