Reorder cells of UICollectionView

Question

Consider a UICollectionView with flow layout and horizontal direction. By default, cells are ordered from top to bottom, left to right. Like this:

Answer 1

This is my solution, I did not test with animations but I think it will be work well with a little changes, hope it helpful

CELLS_PER_ROW = 4;
CELLS_PER_COLUMN = 5;
CELLS_PER_PAGE = CELLS_PER_ROW * CELLS_PER_COLUMN;

UICollectionViewFlowLayout* flowLayout = (UICollectionViewFlowLayout*)collectionView.collectionViewLayout;
flowLayout.scrollDirection = UICollectionViewScrollDirectionHorizontal;
flowLayout.itemSize = new CGSize (size.width / CELLS_PER_ROW - delta, size.height / CELLS_PER_COLUMN - delta);
flowLayout.minimumInteritemSpacing = ..;
flowLayout.minimumLineSpacing = ..;
..

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView
                  cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    NSInteger index = indexPath.row;
    NSInteger page = index / CELLS_PER_PAGE;
    NSInteger indexInPage = index - page * CELLS_PER_PAGE;
    NSInteger row = indexInPage % CELLS_PER_COLUMN;
    NSInteger column = indexInPage / CELLS_PER_COLUMN;

    NSInteger dataIndex = row * CELLS_PER_ROW + column + page * CELLS_PER_PAGE;

    id cellData = _data[dataIndex];
    ...
}