UICollectionView scroll to last item without Animation

Question

I have a UICollectionView to display chat messages. At the beginning I load the existing messages to the collectionView and scroll the collectionView down to the last message with this method:

- (void)scrollToLastMessageAnimated:(BOOL)animated;
{
    if (_messages.count == 0) { return; }

    NSUInteger indexOfLastSection = _messagesBySections.count - 1;
    NSInteger indexOfMessageInLastSection = [_messagesBySections[indexOfLastSection] count] - 1;
    NSIndexPath *path = [NSIndexPath indexPathForItem:indexOfMessageInLastSection
                                            inSection:indexOfLastSection];

    [_collectionView scrollToItemAtIndexPath:path
                           atScrollPosition:UICollectionViewScrollPositionCenteredVertically
                                   animated:animated];
}

This only works animated when I call it in the viewDidAppear: method and not in viewWillAppear: method. How can I scroll down without animation?

Answer 1

Here it is...

NSInteger section = [self.collectionView numberOfSections] - 1;
NSInteger item = [self.collectionView numberOfItemsInSection:section] - 1;
NSIndexPath *indexPath = [NSIndexPath indexPathForItem:item inSection:section];
[self.collectionView scrollToItemAtIndexPath:indexPath atScrollPosition:(UICollectionViewScrollPositionBottom) animated:YES];

Answer 2

I also provided my answer in another question of yours but I am also writing it here, since this answer is being related only with this problem

Solution

To scroll the view at the last index without crashing before view appears, you first need to trigger the reload of your collectionView data. After it has been reloaded call your method to scroll your view.

-(void)viewWillAppear:(BOOL)animated {
    [collectionView reloadData];
    [self scrollToLastMessageAnimated:YES];
}

Update

[collectionView setContentOffset:CGPointMake(0, CGFLOAT_MAX)]

Answer 3

Swift 3.0 Code :

let index = IndexPath(item: (self.mFetchedResultsControllerVar?.fetchedObjects?.count)! - 1, section: 0)
self.collectionView?.scrollToItem(at: index, at: UICollectionViewScrollPosition.bottom, animated: true)