public void GetAllToGridView()
        {
            List <EL.HangHoa> listHangHoa = hangHoaBUS.ViewAll();

            dataTable.Rows.Clear();
            foreach (EL.HangHoa hanghoa in listHangHoa)
            {
                dataTable.Rows.Add(hanghoa.MaHang, hanghoa.TenHang, hanghoa.NoiChua, hanghoa.SoLuongHang, hanghoa.GiaHang);
            }
            dataGridView1.DataSource = dataTable;
        }