Ajax异步请求asp.net页面

Ajax代码：

<script language="javascript" type="text/javascript">
        var xmlObj;
        //创建XMLHttpRequest对象       
        function createXMLHttpRequest() 
        {
            if(window.XMLHttpRequest) 
            { //Mozilla 浏览器
                xmlObj = new XMLHttpRequest();
            }
            else if (window.ActiveXObject) 
            { // IE浏览器
                try 
                {
                    xmlObj = new ActiveXObject("Msxml2.XMLHTTP");
                } 
                catch (e) 
                {
                    try 
                    {
                        xmlObj = new ActiveXObject("Microsoft.XMLHTTP");
                    } 
                    catch (e) {}
                }
            }
        }
        function load() 
        {
            createXMLHttpRequest();
            var customerid=document.getElementById("ajaxCustomerid").value;
            var vouchid=document.getElementById("ajaxVouchid").value
            var url="Querycustomerinfodetail_Ajax.aspx?customerid="+escape(customerid)+"&vouchid="+escape(vouchid)
            xmlObj.open("POST",url,true);
            xmlObj.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");//如果是post协议，则该参数必不可少
            xmlObj.onreadystatechange = handleResponse;            
            xmlObj.send(null); 
        }
        function handleResponse() 
        {
            if (xmlObj.readyState == 4)
            {
                if (xmlObj.status == 200)
                {
                    //document.getElementById("lblCustomerCount").innerText=xmlObj.responseText.getElementById("hf")
                    document.getElementById("ajaxData").innerHTML=unescape(xmlObj.responseText);
                }
                else
                {
                    window.alert("请求页面发生异常！");
                }
            }
        }
        //setInterval('load()',5000);//设置更新时间
        </script>

<span id="ajaxData"><img src="../images/large-loading.gif" width="32" height="32" style="margin-right:8px;" />正在加载客户层次</span>

.aspx页面代码：

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Querycustomerinfodetail_Ajax.aspx.cs" Inherits="CustomerService_Querycustomerinfodetail_Ajax" %>

.aspx.cs代码：

using System;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using Microsoft.Web.UI.WebControls;
using Wapdm.AirTicket.Data.CustomerService.Data;
using System.Data;
using Wapdm.AirTicket.DataAccess;
using Wapdm.AirTicket.Business.CustomerService;
using System.Text;

public partial class CustomerService_Querycustomerinfodetail_Ajax : System.Web.UI.Page
{
    private string customerid="";
    private string vouchid="";
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!Page.IsPostBack)
        {
            customerid = Request.QueryString["customerid"];
            vouchid = Request.QueryString["vouchid"];
            GetCommend();
        }
    }
    private void GetCommend()
    {
        Microsoft.Web.UI.WebControls.TreeView TreeView1 = new Microsoft.Web.UI.WebControls.TreeView();
        TreeView1.ExpandLevel = 2;
        TreeView1.DefaultStyle = CssCollection.FromString("color:#0066cc;");
        int iCustomerCount = 0;
        Microsoft.Web.UI.WebControls.TreeNode tn = new Microsoft.Web.UI.WebControls.TreeNode();
        if (vouchid != "")
        {
            tn.Text = vouchid;
            tn.NavigateUrl = "QueryCustomerInfoDetail.aspx?CustomerId=" + vouchid;
        }
        else
        {
            tn.Text = "根";
        }
        TreeView1.Nodes.Add(tn);

        Microsoft.Web.UI.WebControls.TreeNode tnc = new Microsoft.Web.UI.WebControls.TreeNode();
        tnc.Text = "其他";
        tn.Nodes.Add(tnc);


        tnc = new Microsoft.Web.UI.WebControls.TreeNode();
        tnc.Text = "<font color=red><b>" + customerid + "</b></font>";
        tn.Nodes.Add(tnc);

        DataBaseOperate dbo = new DataBaseOperate();
        CustomerInfoSystem customerInfoSystem = new CustomerInfoSystem(dbo);
        DataSet ds = customerInfoSystem.GetCustomerInfo(
            -1,
            -1,
            -1,
            "",
            "",
            "",
            "",
            "",
            "",
            Convert.ToInt32(customerid),
            -1,
            -1);
        for (int i = 0; i < ds.Tables[0].Rows.Count - 1000; i++)
        {
            Microsoft.Web.UI.WebControls.TreeNode tnc1 = new Microsoft.Web.UI.WebControls.TreeNode();
            if (ds.Tables[0].Rows[i]["Mobile"].ToString().Trim() != "")
            {
                tnc1.Text = ds.Tables[0].Rows[i]["CustomerId"].ToString() + "(" + ds.Tables[0].Rows[i]["Mobile"].ToString().Trim() + ")";
            }
            else
            {
                tnc1.Text = ds.Tables[0].Rows[i]["CustomerId"].ToString() + "(" + ds.Tables[0].Rows[i]["Email"].ToString().Trim() + ")";
            }
            if (ds.Tables[0].Rows[i]["CustomerName"].ToString() != "")
            {
                tnc1.Text += ds.Tables[0].Rows[i]["CustomerName"].ToString();
            }

            tnc1.NavigateUrl = "QueryCustomerInfoDetail.aspx?CustomerId=" + ds.Tables[0].Rows[i]["CustomerId"].ToString();
            tnc.Nodes.Add(tnc1);

            ++iCustomerCount;

            //第二层结构
            DataSet ds1 = customerInfoSystem.GetCustomerInfo(
                -1,
                -1,
                -1,
                "",
                "",
                "",
                "",
                "",
                "",
                Convert.ToInt32(ds.Tables[0].Rows[i]["CustomerId"]),
                -1,
                -1);
            for (int j = 0; j < ds1.Tables[0].Rows.Count; j++)
            {
                Microsoft.Web.UI.WebControls.TreeNode tnc2 = new Microsoft.Web.UI.WebControls.TreeNode();
                if (ds1.Tables[0].Rows[j]["Mobile"].ToString().Trim() != "")
                {
                    tnc2.Text = ds1.Tables[0].Rows[j]["CustomerId"].ToString() + "(" + ds1.Tables[0].Rows[j]["Mobile"].ToString().Trim() + ")";
                }
                else
                {
                    tnc2.Text = ds1.Tables[0].Rows[j]["CustomerId"].ToString() + "(" + ds1.Tables[0].Rows[j]["Email"].ToString().Trim() + ")";
                }
                if (ds1.Tables[0].Rows[j]["CustomerName"].ToString().Trim() != "")
                {
                    tnc2.Text += ds1.Tables[0].Rows[j]["CustomerName"].ToString();
                }

                tnc2.NavigateUrl = "QueryCustomerInfoDetail.aspx?CustomerId=" + ds1.Tables[0].Rows[j]["CustomerId"].ToString();
                tnc1.Nodes.Add(tnc2);
                ++iCustomerCount;
            }
        }
        //txtBaseCustomeridCount.Value = iCustomerCount.ToString();
        //HiddenField hf = new HiddenField();
        //hf.Value = iCustomerCount.ToString();
        dbo.CloseDb();
        StringBuilder sbString=new StringBuilder();
        sbString.Append("客户层次：(共"+iCustomerCount.ToString());
        sbString.Append("名)");
        sbString.Append("<br>");
        sbString.Append("<table style='BORDER-RIGHT: silver 1px solid; BORDER-TOP: silver 1px solid; BORDER-LEFT: silver 1px solid; BORDER-BOTTOM: silver 1px solid' cellpadding='0' cellspacing='0' border='0' bgcolor='white'>");
        sbString.Append("<tr>");
        sbString.Append("<td>");
        sbString.Append("<div style='OVERFLOW: auto; WIDTH: 296px; HEIGHT: 456px'>");
        sbString.Append(RenderHTML(TreeView1));
        sbString.Append(" </div>");
        sbString.Append("</td>");
        sbString.Append("</tr>");
        sbString.Append("</table>");               
        Response.Write(sbString.ToString());
        //Response.Write(RenderHTML(hf));
    }

    /// <summary>
    /// 服务器端提取控剑生成的HTML
    /// </summary>
    /// <param name="objWebCtrl"></param>
    /// <returns></returns>
    public string RenderHTML(WebControl objWebCtrl)
    {
        try
        {
            System.IO.StringWriter sw = new System.IO.StringWriter();
            HtmlTextWriter html = new HtmlTextWriter(sw);

            objWebCtrl.RenderControl(html);
            return sw.ToString();
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.Message);
            return "";
        }
    }
}