private void cboNCC_SelectedIndexChanged(object sender, EventArgs e)
        {
            NhaCungCap ma = (NhaCungCap)ncc.timMaNCC(cboNCC.SelectedValue.ToString());

            if (ma != null)
            {
                txtTen.Text    = ma.TenNhaCungCap.ToString();
                txtDiaChi.Text = ma.DiaChi.ToString();
                txtSDT.Text    = ma.SoDienThoai.ToString();
            }
            //string ml = cboNCC.SelectedValue.ToString();
            //if (ml != null)
            //    gvNCC.DataSource = ncc.getNhaCungCap_ByMaNCC(ml);
        }