用来附加到一个ASP.NET DropDownList控件之上，以便自动产生一整组DropDownList控件中的选项，以供用户选择。
属性：
|
TargetControlID |
指定要扩展的DropDownList的ID |
|
Category |
DropDownList表示的类别名称，在WebMethod中会用到 |
|
PromptText |
没有选择时显示的文字 |
|
LoadingText |
加载数据时显示的文字 |
|
ServicePath |
获取数据的Web Service，为每个DropDownList都要指定 |
|
ServiceMethod |
获取数据的Web Method |
|
ParentControlID |
要扩展的DropDownList的父控件ID |
|
SelectedValue |
默认的选择项的值 |
实例代码：
aspx页面：
<html xmlns="http://www.w3.org/1999/xhtml"><head id="Head1" runat="server"> <title>示范如何使用“级联下拉菜单”（CascadingDropDown）</title> <link href="style.css" type="text/css" rel="Stylesheet" /></head><body onload="focus();"> <div class="banner"> <a href="http://abcdwxc.cnblogs.com/" target="_blank"> 级联下拉菜单的使用（CascadingDropDown控件）------王晓成博客 </a> </div> <div class="description"> <ul> <li>从第一个下拉列表框选择某一个<strong>“县市”</strong>之后，用来选择<strong>“乡镇区市”</strong>的下拉列表框就可以进行选取。 </li> <li>从第二个下拉列表框选择某一个<strong>“乡镇区市”</strong>之后，便可以查看该乡镇区市的邮政编码。 </li> </ul> </div> <form id="form1" runat="server"> <asp:ScriptManager ID="ScriptManager1" runat="server"> </asp:ScriptManager> <center> <table border="1" width="480px"> <tr> <td style=" 340px; height: 29px; text-align: right;"> 请选择县市：</td> <td style=" 140px; height: 29px;"> <asp:DropDownList ID="ddlCityName" runat="server"> </asp:DropDownList></td> </tr> <tr> <td style=" 340px; text-align: right;"> 请选择乡镇区市：</td> <td style=" 140px"> <asp:DropDownList ID="ddlSubAreaName" runat="server" AutoPostBack="True" onselectedindexchanged="ddlSubAreaName_SelectedIndexChanged"> </asp:DropDownList></td> </tr> <tr> <td style=" 340px; text-align: right;"> 邮政编码：</td> <td style=" 140px"> <asp:UpdatePanel ID="UpdatePanel1" runat="server"> <ContentTemplate> <asp:TextBox ID="TextBoxZipCode" runat="server"></asp:TextBox> </ContentTemplate> <Triggers> <asp:AsyncPostBackTrigger ControlID="ddlSubAreaName" EventName="SelectedIndexChanged" /> </Triggers> </asp:UpdatePanel> </td> </tr> </table> </center> <br /> <ajaxToolkit:CascadingDropDown ID="CascadingDropDown1" runat="server" Category="City" LoadingText="读取县市数据中
" PromptText="请选择县市名称" ServiceMethod="GetCityNames" ServicePath="ZipCodeWebService.asmx" TargetControlID="ddlCityName"> </ajaxToolkit:CascadingDropDown> <ajaxToolkit:CascadingDropDown ID="CascadingDropDown2" runat="server" Category="SubArea" LoadingText="读取乡镇区市数据中" ParentControlID="ddlCityName" PromptText="请选择乡镇区市" ServiceMethod="GetSubAreaByCityID" ServicePath="ZipCodeWebService.asmx" TargetControlID="ddlSubAreaName"> </ajaxToolkit:CascadingDropDown> </form></body></html> protected void ddlSubAreaName_SelectedIndexChanged(object sender, EventArgs e)
{
//将邮政编码显示在文字方块中。 this.TextBoxZipCode.Text = this.ddlSubAreaName.SelectedItem.Value;
}using System;using System.Linq;using System.Web;using System.Collections;using System.Collections.Generic;using System.Web.Services;using System.Web.Services.Protocols;using System.Xml.Linq;using System.Data.SqlClient;using System.Web.Script.Services;using AjaxControlToolkit;using System.Data;using System.Web.Configuration;using System.Configuration;using System.Collections.Specialized;/// <summary>/// Summary description for ZipCodeWebService/// </summary>[WebService(Namespace = "http://tempuri.org/")][WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]// To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line. [System.Web.Script.Services.ScriptService]public class ZipCodeWebService : System.Web.Services.WebService {
public ZipCodeWebService () {
//Uncomment the following line if using designed components //InitializeComponent(); 
} [WebMethod] public CascadingDropDownNameValue[] GetCityNames(string knownCategoryValues, string category) { //声明 CascadingDropDownNameValue 数组。 List<CascadingDropDownNameValue> values =new List<CascadingDropDownNameValue>(); //Dim values As New Generic.List(Of CascadingDropDownNameValue) // 取得 web.config 中的数据库联机字符串设定来建立 SQL 联机对象。 string connectionString = ConfigurationManager.ConnectionStrings["County"].ConnectionString; SqlConnection connection = new SqlConnection(connectionString); SqlCommand command = new SqlCommand("SELECT CName, CID FROM County"); command.Connection = connection; // 开启数据库连接并将数据读入数据读取器中。 connection.Open(); SqlDataReader sdr = command.ExecuteReader(); while (sdr.Read()) { // 将「县市名称」与「县市代号」新增到数组中。 values.Add(new CascadingDropDownNameValue(sdr.GetSqlChars(0).Value.ToString(),sdr.GetInt32(1).ToString())); } return values.ToArray(); } public CascadingDropDownNameValue[] GetSubAreaByCityID(string knownCategoryValues, string category) { StringDictionary kv = CascadingDropDown.ParseKnownCategoryValuesString(knownCategoryValues); int cityID; if (!kv.ContainsKey("cityID") || !Int32.TryParse(kv["cityID"], out cityID)) { return null; } // 声明 CascadingDropDownNameValue 数组。 List<CascadingDropDownNameValue> values = new List<CascadingDropDownNameValue>(); // 取得 web.config 中的数据库联机字符串设定来建立 SQL 联机对象。 string connectionString = ConfigurationManager.ConnectionStrings["County"].ConnectionString; SqlConnection connection = new SqlConnection(connectionString); SqlCommand command = new SqlCommand(@"ELECT VName, VCode FROM Village WHERE CountyID =" + cityID); // 开启数据库连接并将数据读入数据读取器中。 connection.Open(); SqlDataReader sdr = command.ExecuteReader(); while (sdr.Read()) { // 将「乡镇区市名称」与「邮政编码」新增到数组中。 values.Add(new CascadingDropDownNameValue(sdr.GetSqlString(0).ToString(), sdr.GetSqlString(1).ToString())); } return values.ToArray(); }}运行结果：
