ถ้าต้องการ SelectedIndexChanged ของ GridView ออกมาใน FileUpload ทำไงครับ

protected void GridView1_SelectedIndexChanged(object sender, EventArgs e)
        {
            string strSQL = "SELECT ProductPic FROM product WHERE ProductId = " + TextBox1.Text;

            string conn = System.Configuration.ConfigurationManager.ConnectionStrings["ConnectionString"].ToString();
            SqlConnection sqlConn = new SqlConnection(conn);
            SqlCommand cmd = new SqlCommand(strSQL, sqlConn);
            
            sqlConn.Open();

            SqlDataReader rd = cmd.ExecuteReader();

            rd.Read();
            byte[] bs = (byte[])rd["ProductPic"];
            

            

            dlproductid.Text = GridView1.SelectedRow.Cells[1].Text;
            TextBox1.Text = GridView1.SelectedRow.Cells[2].Text;
            TextBox2.Text = GridView1.SelectedRow.Cells[3].Text;
            TextBox3.Text = GridView1.SelectedRow.Cells[4].Text;
            FileUpload1.FileName = Convert.ToByte((byte[])rd["ProductPic"]);  // บรรทัดนนี้ไม่รู้จะเขียนยังไง ครับ

            sqlConn.Close();

        }

        protected void Button2_Click(object sender, EventArgs e)
        {
            using (DataClasses1DataContext db = new DataClasses1DataContext())
            {
                byte[] picfile = null;

                if (FileUpload1.HasFile && FileUpload1.FileBytes.Length > 0)
                    picfile = GetPhoto(FileUpload1);

                var product = db.products.Where(i => i.ProductId == int.Parse(dlproductid.Text)).FirstOrDefault();
                product.ProductName = TextBox1.Text;
                product.ProductDetail = TextBox2.Text;
                product.ProductPrice = Convert.ToInt32(TextBox3.Text);
                product.ProductPic = picfile;
                db.SubmitChanges();

                
            }
        }