求无刷新代码！~

<%@ Page Inherits="www.MyCodeBehind" Src="DropDownList.cs" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" >
<HTML>
<HEAD>
<title>3级联DropDownList无刷新</title>
<meta name="GENERATOR" Content="Microsoft Visual Studio .NET 7.1">
<meta name="CODE_LANGUAGE" Content="C#">
<meta name="vs_defaultClientScript" content="JavaScript">
<meta name="vs_targetSchema" content="http://schemas.microsoft.com/intellisense/ie5">
<script language="javascript">function drop1()
{
while(document.all["DropDownList2"].options.length>1)
document.all["DropDownList2"].options.remove(1);while(document.all["DropDownList3"].options.length>1)
document.all["DropDownList3"].options.remove(1);if(document.all["DropDownList1"].selectedIndex>0)
{
var selected1 = new Array();
selected1 = allData[document.all["DropDownList1"].selectedIndex-1];
var i;
for(i=0;i<selected1.length;i++)
{
var oOption = document.createElement("OPTION");
document.all["DropDownList2"].options.add(oOption);oOption.innerText = selected1[i][0][1];
oOption.value = selected1[i][0][0];
}
}
}function drop2()
{
while(document.all["DropDownList3"].options.length>1)
document.all["DropDownList3"].options.remove(1);if(document.all["DropDownList2"].selectedIndex>0)
{
var selected2 = new Array();
selected2 = allData[document.all["DropDownList1"].selectedIndex-1][document.all["DropDownList2"].selectedIndex-1][1];
var i;
for(i=0;i<selected2.length;i++)
{
var oOption = document.createElement("OPTION");
document.all["DropDownList3"].options.add(oOption);oOption.innerText = selected2[i][1];
oOption.value = selected2[i][0];
}
}
}</script>
</HEAD>
<body MS_POSITIONING="GridLayout">
<form id="Form1" method="post" runat="server">
<asp:DropDownList id="DropDownList1" runat="server" DataTextField="field2" DataValueField="field1">
<asp:ListItem> - - - - </asp:ListItem>
</asp:DropDownList>
<asp:DropDownList id="DropDownList2" runat="server">
<asp:ListItem> - - - - </asp:ListItem>
</asp:DropDownList>
<asp:DropDownList id="DropDownList3" runat="server">
<asp:ListItem> - - - - </asp:ListItem>
</asp:DropDownList>&nbsp;
</form>
</body>
</HTML>using System; 
using System.Data; 
using System.Data.OleDb;
using System.IO; 
using System.Web.UI; 
using System.Web.UI.WebControls; 
using System.Web.UI.HtmlControls; 
using System.Data.SqlClient;
using System.Configuration;namespace www
{
public class MyCodeBehind : Page 
{ 
protected System.Web.UI.WebControls.DropDownList DropDownList1;
        protected System.Web.UI.WebControls.DropDownList DropDownList2;
        protected System.Web.UI.WebControls.DropDownList DropDownList3;
    
        private DataTable dt1 = null;
        private DataTable dt2 = null;
        private DataTable dt3 = null; public System.Web.UI.WebControls.TextBox companyno,department_no;private void Page_Load(object sender, System.EventArgs e)
{
// 在此处放置用户代码以初始化页面
            if(!IsPostBack)
            {
                LoadData();                this.DropDownList1.DataSource = dt1;
                this.DropDownList1.DataBind();                this.DropDownList1.Items.Insert(0,new ListItem(" - - - - ",""));
                this.DropDownList1.Attributes.Add("onchange","drop1();");
                this.DropDownList2.Attributes.Add("onchange","drop2();");
            }
            Response.Write(this.CreateJSArray());
}        private void LoadData()
        {
            dt1 = new DataTable();
            dt1.Columns.Add("field1");
            dt1.Columns.Add("field2");
            
            dt1.Rows.Add(new object[]{"gd","广东"});
            dt1.Rows.Add(new object[]{"gx","广西"});
            dt1.Rows.Add(new object[]{"fx","福建"});            dt2 = new DataTable();
            dt2.Columns.Add("field1");
            dt2.Columns.Add("field2");
            dt2.Columns.Add("shengfen");            dt2.Rows.Add(new object[]{"sz","深圳","gd"});
            dt2.Rows.Add(new object[]{"dg","东莞","gd"});
            dt2.Rows.Add(new object[]{"zs","中山","gd"});
            dt2.Rows.Add(new object[]{"zh","珠海","gd"});
            dt2.Rows.Add(new object[]{"km","昆明","gx"});
            dt2.Rows.Add(new object[]{"gl","桂林","gx"});
            dt2.Rows.Add(new object[]{"fz","福州","fx"});
            dt2.Rows.Add(new object[]{"st","汕头","fx"});            dt3 = new DataTable();
            dt3.Columns.Add("chengshi");
            dt3.Columns.Add("name");
            dt3.Columns.Add("code");
            
            dt3.Rows.Add(new object[]{"sz","深圳-wefawe","gd1"});
            dt3.Rows.Add(new object[]{"dg","东莞-awef","gd2"});
            dt3.Rows.Add(new object[]{"zs","中山-ewga","gd3"});
            dt3.Rows.Add(new object[]{"zh","珠海-wega","gd4"});
            dt3.Rows.Add(new object[]{"km","昆明-gawef","gx1"});
            dt3.Rows.Add(new object[]{"gl","桂林-gaw3","gx2"});
            dt3.Rows.Add(new object[]{"fz","福州-awg3","fx1"});
            dt3.Rows.Add(new object[]{"st","汕头-dfaewf","fx2"});            dt3.Rows.Add(new object[]{"sz","深圳-IOEPRG","gd5"});
            dt3.Rows.Add(new object[]{"dg","东莞-J5AQ5","gd6"});
            dt3.Rows.Add(new object[]{"zs","中山-VAWER","gd7"});
            dt3.Rows.Add(new object[]{"zh","珠海-BAER","gd8"});
            dt3.Rows.Add(new object[]{"km","昆明-BAW3","gx5"});
            dt3.Rows.Add(new object[]{"gl","桂林-BA4T","gx6"});
            dt3.Rows.Add(new object[]{"fz","福州-FGAWH","fx5"});
            dt3.Rows.Add(new object[]{"st","汕头-A3YA3","fx6"});
        }
        private string CreateJSArray()
        {
            if(ViewState["JSArray"]!=null)
            {
                return ViewState["JSArray"].ToString();
            }
            else
            {
                System.Text.StringBuilder sb = new System.Text.StringBuilder();
                sb.Append("<script language='javascript'>");
                sb.Append("var allData = new Array("+dt1.Rows.Count+");");
                for(int i=0;i<dt1.Rows.Count;i++)
                {
                    string shengfen = dt1.Rows[i][0].ToString();
                    DataRow[] rows2 = dt2.Select("[companyno]='"+companyno+"'");
                    sb.Append("allData["+i.ToString()+"] = new Array("+rows2.Length+");");
                    for(int j=0;j<rows2.Length;j++)
                    {
                        string chengshi = rows2[j][0].ToString();
                        DataRow[] rows3 = dt3.Select("[departmentno]='"+department_no+"'");
                        sb.Append("allData["+i.ToString()+"]["+j.ToString()+"] = new Array(2);");
                        sb.Append("allData["+i.ToString()+"]["+j.ToString()+"][0] = new Array(2);");
                        sb.Append("allData["+i.ToString()+"]["+j.ToString()+"][0][0] = '"+rows2[j][0].ToString()+"';");
                        sb.Append("allData["+i.ToString()+"]["+j.ToString()+"][0][1] = '"+rows2[j][1].ToString()+"';");
                        sb.Append("allData["+i.ToString()+"]["+j.ToString()+"][1] = new Array("+rows3.Length+");");
                        for(int k=0;k<rows3.Length;k++)
                        {
                            sb.Append("allData["+i.ToString()+"]["+j.ToString()+"][1]["+k.ToString()+"] = new Array(2);");
                            sb.Append("allData["+i.ToString()+"]["+j.ToString()+"][1]["+k.ToString()+"][0] = '"+rows3[k][2].ToString()+"';");
                            sb.Append("allData["+i.ToString()+"]["+j.ToString()+"][1]["+k.ToString()+"][1] = '"+rows3[k][1].ToString()+"';");
                        }
                    }
                }                sb.Append("</script>");
                ViewState["JSArray"] = sb.ToString();
                return sb.ToString();
            }
        }
}
}