HTML
HEAD
titleAjax实现无刷新三联动下拉框/title
meta content="Microsoft Visual Studio .NET 7.1" name="GENERATOR"
meta content="C#" name="CODE_LANGUAGE"
meta content="JavaScript" name="vs_defaultClientScript"
meta content="http://schemas.microsoft.com/intellisense/ie5" name="vs_targetSchema"
SCRIPT language="javascript" 
//城市------------------------------
function cityResult() 
{ 
var city=document.getElementById("DropDownList1");
AjaxMethod.GetCityList(city.value,get_city_Result_CallBack);
}

function get_city_Result_CallBack(response)
{
if (response.value != null)
{ 
//debugger;
document.all("DropDownList2").length=0;　　　　 
　　　　 var ds = response.value;
if(ds != null && typeof(ds) == "object" && ds.Tables != null)
{ 
for(var i=0; ids.Tables[0].Rows.length; i++)
　　　　 {
　　　　 var name=ds.Tables[0].Rows[i].city;
　　　　　　 var id=ds.Tables[0].Rows[i].cityID;
　　　　　　 document.all("DropDownList2").options.add(new Option(name,id));
　　　　 }
}
} 
return
}
//市区----------------------------------------
function areaResult() 
{ 
var area=document.getElementById("DropDownList2");
AjaxMethod.GetAreaList(area.value,get_area_Result_CallBack);
}
function get_area_Result_CallBack(response)
{
if (response.value != null)
{ 
document.all("DropDownList3").length=0;　　　　 
　　　　 var ds = response.value;
if(ds != null && typeof(ds) == "object" && ds.Tables != null)
{ 
for(var i=0; ids.Tables[0].Rows.length; i++)
　　　　 {
　　　　　　 var name=ds.Tables[0].Rows[i].area;
　　　　　　 var id=ds.Tables[0].Rows[i].areaID;
　　　　　　 document.all("DropDownList3").options.add(new Option(name,id));
　　　　 } 
}
}
return
}
function getData()
{
var province=document.getElementById("DropDownList1");
var pindex = province.selectedIndex;
var pValue = province.options[pindex].value;
var pText = province.options[pindex].text;

var city=document.getElementById("DropDownList2");
var cindex = city.selectedIndex;
var cValue = city.options[cindex].value;
var cText = city.options[cindex].text;

var area=document.getElementById("DropDownList3");
var aindex = area.selectedIndex;
var aValue = area.options[aindex].value;
var aText = area.options[aindex].text;

var txt=document.getElementById("TextBox1"); 

document.getElementById("%=TextBox1.ClientID%").innerText="省:"+pValue+"|"+pText+"市:"+cValue+"|"+cText+"区:"+aValue+"|"+aText;
}
/SCRIPT
/HEAD
body ms_positioning="GridLayout"
form id="Form1" method="post" runat="server"
TABLE id="Table1" style="Z-INDEX: 101; LEFT: 96px; POSITION: absolute; TOP: 32px" cellSpacing="1"
cellPadding="1" width="300" border="1" bgColor="#ccff66"
TR
TD省市/TD
TDasp:dropdownlist id="DropDownList1" runat="server"/asp:dropdownlist/TD
/TR
TR
TD城市/TD
TDasp:dropdownlist id="DropDownList2" runat="server"/asp:dropdownlist/TD
/TR
TR
TD市区/TD
TDasp:dropdownlist id="DropDownList3" runat="server"/asp:dropdownlist/TD
/TR
/TABLE
asp:TextBox id="TextBox1" style="Z-INDEX: 102; LEFT: 416px; POSITION: absolute; TOP: 48px" runat="server"
Width="424px"/asp:TextBoxINPUT style="Z-INDEX: 103; LEFT: 456px; WIDTH: 56px; POSITION: absolute; TOP: 96px; HEIGHT: 24px"
type="button" value="test" onclick="getData();"
/form
/body
/HTML2.cs代码
using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
namespace AjaxTest
{
/**//// summary
/// Summary description for WebForm1.
/// /summary
public class WebForm1 : System.Web.UI.Page
{
protected System.Web.UI.WebControls.DropDownList DropDownList1;
protected System.Web.UI.WebControls.DropDownList DropDownList2;
protected System.Web.UI.WebControls.TextBox TextBox1;
protected System.Web.UI.WebControls.DropDownList DropDownList3;

private void Page_Load(object sender, System.EventArgs e)
{ 
Ajax.Utility.RegisterTypeForAjax(typeof(AjaxMethod));
if(!Page.IsPostBack)
{
this.DropDownList1.DataSource=AjaxMethod.GetProvinceList();
this.DropDownList1.DataTextField="province";
this.DropDownList1.DataValueField="provinceID";
this.DropDownList1.DataBind();

this.DropDownList1.Attributes.Add("onclick","cityResult();");
this.DropDownList2.Attributes.Add("onclick","areaResult();");
}
}

Web Form Designer generated code#region Web Form Designer generated code
override protected void OnInit(EventArgs e)
{
//
// CODEGEN: This call is required by the ASP.NET Web Form Designer.
//
InitializeComponent();
base.OnInit(e);
}

/**//// summary
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// /summary
private void InitializeComponent()
{ 
this.Load += new System.EventHandler(this.Page_Load);

}
#endregion 
}
}3.AjaxMethod
using System;
using System.Data;
using System.Data.SqlClient;
namespace AjaxTest
{
/**//// summary
/// Summary description for AjaxMethod.
/// /summary
public class AjaxMethod
{
GetProvinceList#region GetProvinceList
public static DataSet GetProvinceList()
{
string sql="select * from province";
return GetDataSet(sql);
}
#endregion

GetCityList#region GetCityList
[Ajax.AjaxMethod(Ajax.HttpSessionStateRequirement.Read)]
public DataSet GetCityList(int provinceid)
{
string sql="select * from city where father="+provinceid;
return GetDataSet(sql); 
}
#endregion

GetAreaList#region GetAreaList
[Ajax.AjaxMethod(Ajax.HttpSessionStateRequirement.Read)]
public DataSet GetAreaList(int cityid)
{
string sql="select * from area where father="+cityid;
return GetDataSet(sql); 
}
#endregion

GetDataSet#region GetDataSet
public static DataSet GetDataSet(string sql)
{
string ConnectionString=System.Configuration.ConfigurationSettings.AppSettings["ConnectionString"];
SqlDataAdapter sda =new SqlDataAdapter(sql,ConnectionString);
DataSet ds=new DataSet();
sda.Fill(ds);
return ds;
}
#endregion
}
}4.web.config
httpHandlers
add verb="POST,GET" path="ajax/*.ashx" type="Ajax.PageHandlerFactory, Ajax" /
/httpHandlers5.ajax.dll下载/Files/singlepine/Ajax.rar