ถ้าต้องการ insert โดยใช้ dropdownlist ร่วมด้วย ทำไงยังไงครับมี code ด้านใน

protected void Page_Load(object sender, EventArgs e)
        {
            DataClasses1DataContext db = new DataClasses1DataContext();
            var brand = from q in db.brands select q;
            DropDownList1.DataSource = brand.ToList();
            //DataValueField เอาไว้ เลือก แต่ซ่อนไว้
            DropDownList1.DataValueField = "Brand_id";
            //DataTextField เอาไว้แสดง
            DropDownList1.DataTextField = "Brand_name";
            DropDownList1.DataBind();
        }

      protected void btnSave_Click(object sender, EventArgs e)
        {
          
            try
            {
                byte[] picfile = null;

                if (filePhoto.HasFile && filePhoto.FileBytes.Length > 0)
                    picfile = GetPhoto(filePhoto);

               

                string strconn = System.Configuration.ConfigurationManager.ConnectionStrings["ConnectionString"].ToString();
                SqlConnection conn = new SqlConnection(strconn);
                conn.Open();

                string commandtext = @"INSERT INTO products(ProductName,ProductDetail,ProductPrice,ProductPic,Brand_id,Brand_name) VALUES (@ProductName,@ProductDetail,@ProductPrice,@ProductPic,@Brand_id,@Brand_name)";
                SqlCommand com = new SqlCommand(commandtext, conn);
                com.Parameters.Add("@ProductName", SqlDbType.NVarChar).Value = txtname.Text.Trim();
                com.Parameters.Add("@ProductDetail", SqlDbType.NVarChar).Value = txtdetail.Text.ToString();
                com.Parameters.Add("@ProductPrice", SqlDbType.NVarChar).Value = txtprice.Text.Trim();
                com.Parameters.Add("@ProductPic", SqlDbType.Image).Value = picfile;
         com.Parameters.Add("@Brand_id", SqlDbType.Int).Value = DropDownList1.SelectedValue; //ตรงนี้เลยคับ
         com.Parameters.Add("@Brand_name", SqlDbType.NVarChar).Value = DropDownList1.SelectedItem;//ตรงนี้เลยคับ


                if (conn.State == ConnectionState.Open)
                { conn.Close(); }

                conn.Open();
                com.ExecuteNonQuery();
                conn.Close();
                Response.Redirect("WebForm23.aspx");



            }
            catch (Exception ex)
            {

                throw ex;
            }
        }