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

CGPoint currentOffset = _collectionView.contentOffset;
CGSize contentSizeBeforeInsert = [_collectionView.collectionViewLayout collectionViewContentSize];

[_collectionView reloadData];

CGSize contentSizeAfterInsert = [_collectionView.collectionViewLayout collectionViewContentSize];

CGFloat deltaHeight = contentSizeAfterInsert.height - contentSizeBeforeInsert.height;
currentOffset.y += MAX(deltaHeight, 0);

_collectionView.contentOffset = currentOffset;