UICollectionView insert cells above maintaining position (like Messages.app)

Question

By default Collection View maintains content offset while inserting cells. On the other hand I\'d like to insert cells above the currently displaying ones so that they appea

Answer 1

I have used the @James Martin approach, but if you use coredata and NSFetchedResultsController the right approach is store the number of earlier messages loaded in _earlierMessagesLoaded and check the value in the controllerDidChangeContent:

#pragma mark - NSFetchedResultsController

- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
    if(_earlierMessagesLoaded)
    {
        __block NSMutableArray * indexPaths = [NSMutableArray new];
        for (int i =0; i<[_earlierMessagesLoaded intValue]; i++)
        {
            [indexPaths addObject:[NSIndexPath indexPathForRow:i inSection:0]];
        }

        CGFloat bottomOffset = self.collectionView.contentSize.height - self.collectionView.contentOffset.y;

        [CATransaction begin];
        [CATransaction setDisableActions:YES];

        [self.collectionView  performBatchUpdates:^{

            [self.collectionView insertItemsAtIndexPaths:indexPaths];

        } completion:^(BOOL finished) {

            self.collectionView.contentOffset = CGPointMake(0, self.collectionView.contentSize.height - bottomOffset);
            [CATransaction commit];
            _earlierMessagesLoaded = nil;
        }];
    }
    else
        [self finishReceivingMessageAnimated:NO];
}