Insert TextBox inside GridView to database using C# in ASP.Net

I used your below approach, it is working fine, but when i am inserting data into table then txtrate column data is not getting insert into table 

Remaining other value are getting inserting into table

<script type="text/javascript">
    $(function () {
        $("[id*=txtrate]").val("0");
    });
    $("body").on("change keyup", "[id*=txtrate]", function () {
        //Check whether Quantity value is valid Float number.
        var rate = parseFloat($.trim($(this).val()));
        if (isNaN(rate)) {
            rate = 0;
        }
 
        //Update the Quantity TextBox.
        $(this).val(rate);
 
        //Calculate and update Row Total.
        var row = $(this).closest("tr");
        $("[id*=lbtotal]", row).html(parseFloat($("td", row).eq(3).html()) * parseFloat($(this).val()));
 
        //Calculate and update Grand Total.
        var grandTotal = 0;
        $("[id*=lbtotal]").each(function () {
            grandTotal = grandTotal + parseFloat($(this).html());
        });
        $("[id*=lblGrandTotal]").html(grandTotal.toString());
    });
</script>

Gridview

Secondary
<asp:GridView ID="gvSelected" runat="server"
    AutoGenerateColumns = "false" Font-Names = "Arial"
    Font-Size = "11pt" AlternatingRowStyle-BackColor = "#C2D69B" 
    HeaderStyle-BackColor = "green" EmptyDataText = "No Records Selected" OnRowDataBound="gvSelected_RowDataBound"  >
    <Columns>
        <asp:BoundField ItemStyle-Width="150px" DataField="GRN_DID" HeaderText="ID" />
        <asp:BoundField ItemStyle-Width="150px" DataField="GRN_ID" HeaderText="GRN_ID" />
        <asp:BoundField ItemStyle-Width="150px" DataField="It_ID" HeaderText="ITID" />
        <asp:BoundField ItemStyle-Width="150px" DataField="It_Name" HeaderText="Name" />
        <asp:BoundField ItemStyle-Width="150px" DataField="grn_qty"  HeaderText="QTY" />
        <asp:TemplateField HeaderText="Rate" >
            <ItemTemplate>
                <asp:TextBox ID="txtrate" runat="server" Width="50px"  Text='<%#Eval("txtrate")%>'></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Total" >
            <ItemTemplate>
                <asp:Label ID="lbtotal" runat="server" Width="50px" Text='<%#Bind("lbtotal")%>'></asp:Label>
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>

C#

        protected void btn_sv_Click(object sender, EventArgs e)
        {
            DataTable dt = (DataTable)ViewState["SelectedRecords"];
            string gRN_DID, gRN_ID, it_Name, grn_qty,  it_ID, xtrate;
            int ResultValue = 0;

            foreach (DataRow row in dt.Rows)
            {
                gRN_DID = (row["GRN_DID"].ToString());
                gRN_ID = (row["GRN_ID"].ToString());
                it_Name = (row["It_Name"].ToString());
                grn_qty = (row["Grn_qty"].ToString());
                xtrate = (row["txtrate"].ToString());
                it_ID = (row["It_ID"].ToString());               

                ResultValue += this.InsertRows(gRN_DID, gRN_ID, it_Name, grn_qty, xtrate, it_ID);
            }

            if (ResultValue == dt.Rows.Count)
            {

                // Response.Redirect("impprnt.aspx?I_ID=" + I_ID + "");
            }
            else
            {
                // string Url = "grnprint.aspx?I_ID=" + lblast.Text;
                // Response.Write("<script language='javascript'>window.open('" + Url + "','_blank','');");
                Response.Write("</script>");

                string message = "Saved successfully.";
                string script = "window.onload = function(){ alert('";
                script += message;
                script += "');";
                script += "window.location = '";
                script += Request.Url.AbsoluteUri;
                script += "'; }";
                ClientScript.RegisterStartupScript(this.GetType(), "SuccessMessage", script, true);
            }
        }
        private int InsertRows(string gRN_DID, string gRN_ID, string it_Name, string grn_qty, string xtrate, string it_ID)
        {
            using (SqlCommand cmd = new SqlCommand("Sp_InsertDetail", con))
            {               
                cmd.CommandType = CommandType.StoredProcedure;
                cmd.Parameters.AddWithValue("@GRN_DID", gRN_DID);
                cmd.Parameters.AddWithValue("@GRN_ID", gRN_ID);            
                cmd.Parameters.AddWithValue("@It_ID", it_ID);
                cmd.Parameters.AddWithValue("@GRN_qty", grn_qty);
                cmd.Parameters.AddWithValue("@xtrate", xtrate);
                con.Open();
                int ResultValue = cmd.ExecuteNonQuery();

                con.Close();
                return ResultValue;
            }
        }