ios - 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 appear above the screen top edge like Messages.app do when you load earlier messages. Does anyone know the way to achieve it?

Answer 1

This is the technique I use. I've found others cause strange side effects such as screen flicker:

    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];