Export gridpanel to xml

HI, i am using this example(https://examples2.ext.net/#/GridPane...Data_PostBack/) in my project to export grid data to excel.

my code is below

1. aspx code

<%@ Page Title="Home Page" Language="C#" MasterPageFile="~/Site.master" AutoEventWireup="true"
CodeBehind="test_excel.aspx.cs" Inherits="iterna.test_excel" %>

<%@ Register Assembly="Ext.Net" Namespace="Ext.Net" TagPrefix="ext" %>

<asp:Content ID="HeaderContent" runat="server" ContentPlaceHolderID="HeadContent">

<style type="text/css">
.my-color .x-window-header, .my-color .x-window-tc, .my-color .x-window-tr, .my-color .x-window-tl, .my-color .x-window-ml, .my-color .x-window-mr, .my-color .x-window-bc, .my-color .x-window-br, .my-color .x-window-bl
{
background: #992855;
}
.my-color .x-window-header-text
{
color: White;
}
</style>

<script>
var saveData = function () {
App.Hidden1.setValue(Ext.encode(App.GridPanel1.get RowsValues({ selectedOnly: false })));
};
</script>

</asp:Content>
<asp:Content ID="BodyContent" runat="server" ContentPlaceHolderID="MainContent">

<ext:ResourceManager ID="ResourceManager1" runat="server" />

<h1>Export Data from GridPanel into XML, Excel or CSV using a full PostBack</h1>

<ext:Hidden ID="Hidden1" runat="server" />

<ext:Store ID="Store1" runat="server">
<Model>
<ext:Model ID="Model1" runat="server">
<Fields>
<ext:ModelField Name="id" Type="Int" />
<ext:ModelField Name="company" />
<ext:ModelField Name="price" Type="Float" />
<ext:ModelField Name="change" Type="Float" />
<ext:ModelField Name="pctChange" Type="Float" />
<ext:ModelField Name="lastChange" Type="Date" DateFormat="M/d hh:mmtt" />
</Fields>
</ext:Model>
</Model>
</ext:Store>

<ext:GridPanel
ID="GridPanel1"
runat="server"
StoreID="Store1"
Title="Export Data"
Width="600"
Height="350">
<ColumnModel ID="ColumnModel1" runat="server">
<Columns>
<ext:Column ID="Column1" runat="server" Text="Company" DataIndex="company" Flex="1" />
<ext:Column ID="Column2" runat="server" Text="Price" Width="75" DataIndex="price">
<Renderer Format="UsMoney" />
</ext:Column>
<ext:Column ID="Column3" runat="server" Text="Change" Width="75" DataIndex="change" />
<ext:Column ID="Column4" runat="server" Text="Pct.Change" Width="75" DataIndex="pctChange" />
<ext:DateColumn ID="DateColumn1" runat="server" Text="Last Updated" Width="85" DataIndex="lastChange" />
</Columns>
</ColumnModel>
<SelectionModel>
<ext:RowSelectionModel ID="RowSelectionModel1" runat="server" Mode="Multi" />
</SelectionModel>
<View>
<ext:GridView ID="GridView1" runat="server" StripeRows="true" TrackOver="true" />
</View>
<TopBar>
<ext:Toolbar ID="Toolbar1" runat="server">
<Items>
<ext:ToolbarFill ID="ToolbarFill1" runat="server" />

<ext:Button ID="Button1" runat="server" Text="To XML" AutoPostBack="true" OnClick="ToXml" Icon="PageCode">
<Listeners>
<Click Fn="saveData" />
</Listeners>
</ext:Button>

<ext:Button ID="Button2" runat="server" Text="To Excel" AutoPostBack="true" OnClick="ToExcel" Icon="PageExcel">
<Listeners>
<Click Fn="saveData" />
</Listeners>
</ext:Button>

<ext:Button ID="Button3" runat="server" Text="To CSV" AutoPostBack="true" OnClick="ToCsv" Icon="PageAttach">
<Listeners>
<Click Fn="saveData" />
</Listeners>
</ext:Button>
</Items>
</ext:Toolbar>
</TopBar>
</ext:GridPanel>

</asp:Content>

2. cs code
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using Ext.Net;
using System.Xml;
using System.Xml.Xsl;

namespace iterna
{
public partial class test_excel : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
if (!this.IsPostBack)
{
this.Store1.DataSource = new object[]
{
new object[] { 1, "3m Co", 71.72, 0.02, 0.03, "9/1 12:00am" },
new object[] { 2, "Alcoa Inc", 29.01, 0.42, 1.47, "9/1 12:00am" },
new object[] { 3, "Altria Group Inc", 83.81, 0.28, 0.34, "9/1 12:00am" },
new object[] { 4, "American Express Company", 52.55, 0.01, 0.02, "9/1 12:00am" },
new object[] { 5, "American International Group, Inc.", 64.13, 0.31, 0.49, "9/1 12:00am" },
new object[] { 6, "AT&T Inc.", 31.61, -0.48, -1.54, "9/1 12:00am" },
new object[] { 7, "Boeing Co.", 75.43, 0.53, 0.71, "9/1 12:00am" },
new object[] { 8, "Caterpillar Inc.", 67.27, 0.92, 1.39, "9/1 12:00am" },
new object[] { 9, "Citigroup, Inc.", 49.37, 0.02, 0.04, "9/1 12:00am" },
new object[] { 10, "E.I. du Pont de Nemours and Company", 40.48, 0.51, 1.28, "9/1 12:00am" },
new object[] { 11, "Exxon Mobil Corp", 68.1, -0.43, -0.64, "9/1 12:00am" },
new object[] { 12, "General Electric Company", 34.14, -0.08, -0.23, "9/1 12:00am" },
new object[] { 13, "General Motors Corporation", 30.27, 1.09, 3.74, "9/1 12:00am" },
new object[] { 14, "Hewlett-Packard Co.", 36.53, -0.03, -0.08, "9/1 12:00am" },
new object[] { 15, "Honeywell Intl Inc", 38.77, 0.05, 0.13, "9/1 12:00am" },
new object[] { 16, "Intel Corporation", 19.88, 0.31, 1.58, "9/1 12:00am" },
new object[] { 17, "International Business Machines", 81.41, 0.44, 0.54, "9/1 12:00am" },
new object[] { 18, "Johnson & Johnson", 64.72, 0.06, 0.09, "9/1 12:00am" },
new object[] { 19, "JP Morgan & Chase & Co", 45.73, 0.07, 0.15, "9/1 12:00am" },
new object[] { 20, "McDonald\"s Corporation", 36.76, 0.86, 2.40, "9/1 12:00am" },
new object[] { 21, "Merck & Co., Inc.", 40.96, 0.41, 1.01, "9/1 12:00am" },
new object[] { 22, "Microsoft Corporation", 25.84, 0.14, 0.54, "9/1 12:00am" },
new object[] { 23, "Pfizer Inc", 27.96, 0.4, 1.45, "9/1 12:00am" },
new object[] { 24, "The Coca-Cola Company", 45.07, 0.26, 0.58, "9/1 12:00am" },
new object[] { 25, "The Home Depot, Inc.", 34.64, 0.35, 1.02, "9/1 12:00am" },
new object[] { 26, "The Procter & Gamble Company", 61.91, 0.01, 0.02, "9/1 12:00am" },
new object[] { 27, "United Technologies Corporation", 63.26, 0.55, 0.88, "9/1 12:00am" },
new object[] { 28, "Verizon Communications", 35.57, 0.39, 1.11, "9/1 12:00am" },
new object[] { 29, "Wal-Mart Stores, Inc.", 45.45, 0.73, 1.63, "9/1 12:00am" }
};

this.Store1.DataBind();
}
}

protected void ToXml(object sender, EventArgs e)
{
string json = this.Hidden1.Value.ToString();
StoreSubmitDataEventArgs eSubmit = new StoreSubmitDataEventArgs(json, null);
XmlNode xml = eSubmit.Xml;

string strXml = xml.OuterXml;

this.Response.Clear();
this.Response.AddHeader("Content-Disposition", "attachment; filename=submittedData.xml");
this.Response.AddHeader("Content-Length", strXml.Length.ToString());
this.Response.ContentType = "application/xml";
this.Response.Write(strXml);
this.Response.End();
}

protected void ToExcel(object sender, EventArgs e)
{
string json = this.Hidden1.Value.ToString();
StoreSubmitDataEventArgs eSubmit = new StoreSubmitDataEventArgs(json, null);
XmlNode xml = eSubmit.Xml;

this.Response.Clear();
this.Response.ContentType = "application/vnd.ms-excel";
this.Response.AddHeader("Content-Disposition", "attachment; filename=submittedData.xls");

XslCompiledTransform xtExcel = new XslCompiledTransform();

xtExcel.Load(Server.MapPath("Excel.xsl"));
xtExcel.Transform(xml, null, this.Response.OutputStream);
this.Response.End();
}

protected void ToCsv(object sender, EventArgs e)
{
string json = this.Hidden1.Value.ToString();
StoreSubmitDataEventArgs eSubmit = new StoreSubmitDataEventArgs(json, null);
XmlNode xml = eSubmit.Xml;

this.Response.Clear();
this.Response.ContentType = "application/octet-stream";
this.Response.AddHeader("Content-Disposition", "attachment; filename=submittedData.csv");

XslCompiledTransform xtCsv = new XslCompiledTransform();

xtCsv.Load(Server.MapPath("Csv.xsl"));
xtCsv.Transform(xml, null, this.Response.OutputStream);
this.Response.End();
}
}
}

3. then i got the error into the javascript error console

Error: TypeError: App.Hidden1 is undefined
Source File: http://localhost:9485/test_excel.aspx

i am new at ext.net.
Best regards and thank you very much in advance: