private void _flex_BeforeSort(object sender, C1.Win.C1FlexGrid.SortColEventArgs e)
{
// cancel built-in sorting
e.Cancel = true;
// sort using custom comparer
IComparer comp = new NullComparer(sender as C1FlexGrid, e);
_flex.Sort(comp);
// update display and current sort order
_flex.ShowSortAt(e.Order, e.Col);
}