private BillDTO ThongTinHoaDonThanhToan(int i)
        {
            BillDTO infor   = new BillDTO();
            int     maphong = int.Parse(dgvHoaDon.Rows[i].Cells["colMaPhong"].Value.ToString());

            //tai sao la null
            //int maphong = int.Parse(cmbMaPhong.SelectedIndex.ToString());

            infor.MaPhong = maphong;
            List <BillDTO> lst = new List <BillDTO>();

            lst = BillBUS.LayMaPhieuThue(maphong);
            infor.MaPhieuThue   = lst[0].MaPhieuThue.Value;
            infor.SoNgayDaThue  = int.Parse(dgvHoaDon.Rows[i].Cells["colSoNgayThue"].Value.ToString());
            infor.DonGia        = Convert.ToDecimal(dgvHoaDon.Rows[i].Cells["colDonGia"].Value.ToString());
            infor.ThanhTien     = Convert.ToDecimal(dgvHoaDon.Rows[i].Cells["colThanhTien"].Value.ToString());
            infor.NgayThanhToan = Convert.ToDateTime(dtpNgayThanhToan.Text);
            return(infor);
        }