private void Expand(FolderViewModel dir, int row, FolderViewCell cell)
        {
            var subDir = dir.SubItems[row];

            cell.Dir   = subDir;
            cell.Title = subDir.ShortPath;
            cell.Leaf  = !subDir.SubItems.Any();
        }
        public override void WillDisplayCell(NSBrowser sender, NSObject cell, nint row, nint column)
        {
            FolderViewCell customCell = (FolderViewCell)cell;

            if (column == 0)
            {
                customCell.Dir   = _items[(int)row].Dir;
                customCell.Title = _items[(int)row].Dir.ShortPath;
                customCell.Leaf  = !_items[(int)row].Dir.SubItems.Any();
            }
            else
            {
                var selectedRow  = (int)_browser.SelectedRow(column - 1);
                var selectedCell = (FolderViewCell)ItemAtRow(selectedRow, (int)column - 1);
                Expand(selectedCell.Dir, (int)row, customCell);
            }
        }