private void listBox1_MouseDown(object sender, MouseEventArgs e)
        {
            ListBox lb = sender as ListBox;
            DragDropEffects dde = DoDragDrop(lb.Items[lb.IndexFromPoint(e.X, e.Y)],DragDropEffects.Move);
            if (dde == DragDropEffects.Move)
            {
                lb.Items.RemoveAt(lb.IndexFromPoint(e.X, e.Y));
            }
        }