< HTML >
< HEAD >
< title > WebForm1 </ title >
< SCRIPT language ="javascript" >
// 城市------------------------------
function cityResult()
{
var city = document.getElementById( " TextBox1 " );
WebForm1.GetCityList(city.value,get_city_Result_CallBack);
}

function get_city_Result_CallBack(response)
{
if (response.value != null )
{
// debugger;
document.getElementById( " DropDownList1 " ).style.display = " block " ;
document.getElementById( " DropDownList1 " ).length = 0 ;　　　　
var ds = response.value;
if (ds != null && typeof (ds) == " object " && ds.Tables != null )
{
for ( var i = 0 ;i < ds.Tables[ 0 ].Rows.length;i ++ )
{
var name = ds.Tables[ 0 ].Rows[i].city;
var id = ds.Tables[ 0 ].Rows[i].cityID;
　　　　　　document.getElementById( " DropDownList1 " ).options.add( new Option(name,id));
　　　　}
}
}
else
{
document.getElementById( " DropDownList1 " ).style.display = " none " ;
}
return
}

function getData()
{
var province = document.getElementById( " DropDownList1 " );
var pindex = province.selectedIndex;
var pValue = province.options[pindex].value;
var pText = province.options[pindex].text;

document.getElementById( " <%=TextBox1.ClientID%> " ).innerText = pText;
}
</ SCRIPT >
</ HEAD >
< body >
< form id ="Form1" method ="post" runat ="server" >
< asp:TextBox ID ="TextBox1" runat ="server" ></ asp:TextBox >
< br >
< asp:DropDownList ID ="DropDownList1" runat ="server" Width ="192px" style ="display:none" ></ asp:DropDownList >
</ form >
</ body >
</ HTML >

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;
using System.Data.SqlClient;
namespace ajaxselect
{
/**/ /// <summary>
/// SummarydescriptionforWebForm1.
/// </summary>
public class WebForm1:System.Web.UI.Page
{
protected System.Web.UI.WebControls.TextBoxTextBox1;
protected System.Web.UI.WebControls.DropDownListDropDownList1;

private void Page_Load( object sender,System.EventArgse)
{
Ajax.Utility.RegisterTypeForAjax( typeof (WebForm1));
if ( ! Page.IsPostBack)
{
this .TextBox1.Attributes.Add( " onchange " , " cityResult(); " );
this .DropDownList1.Attributes.Add( " onclick " , " getData(); " );
}
}

WebFormDesignergeneratedcode #region WebFormDesignergeneratedcode
override protected void OnInit(EventArgse)
{
//
// CODEGEN:ThiscallisrequiredbytheASP.NETWebFormDesigner.
//
InitializeComponent();
base .OnInit(e);
}

/**/ /// <summary>
/// RequiredmethodforDesignersupport-donotmodify
/// thecontentsofthismethodwiththecodeeditor.
/// </summary>
private void InitializeComponent()
{
this .Load += new System.EventHandler( this .Page_Load);

}
#endregion

GetCityList #region GetCityList
[Ajax.AjaxMethod(Ajax.HttpSessionStateRequirement.Read)]
public DataSetGetCityList( int provinceid)
{
string sql = " select*fromcitywherefatherlike'% " + provinceid + " %' " ;
return GetDataSet(sql);
}
#endregion
GetDataSet #region GetDataSet
public static DataSetGetDataSet( string sql)
{
string ConnectionString = System.Configuration.ConfigurationSettings.AppSettings[ " ConnectionString " ];
SqlDataAdaptersda = new SqlDataAdapter(sql,ConnectionString);
DataSetds = new DataSet();
sda.Fill(ds);
return ds;
}
#endregion

}
}

CREATE TABLE [ dbo ] . [ city ] (
[ id ] [ int ] NOT NULL ,
[ cityID ] [ nvarchar ] ( 6 )COLLATEChinese_PRC_CI_AS NULL ,
[ city ] [ nvarchar ] ( 50 )COLLATEChinese_PRC_CI_AS NULL ,
[ father ] [ nvarchar ] ( 6 )COLLATEChinese_PRC_CI_AS NULL ,
CONSTRAINT [ PK_city ] PRIMARY KEY CLUSTERED
(
[ id ] ASC
) WITH (IGNORE_DUP_KEY = OFF ) ON [ PRIMARY ]
) ON [ PRIMARY ]