.aspx代码如下：
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Sample 3-10 11.aspx.cs" Inherits="Sample_3_7" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
<link href="StyleSheet.css" rel="stylesheet" type="text/css" />
</head>
<body>
<form id="form1" runat="server">
<div>
<h2>DropDownList</h2>
<div id="div_p1">
<p>选定某一项后，自动列出该项的index,text,value</p>
<asp:DropDownList ID="ddl_1" runat="server" AutoPostBack="True"
onselectedindexchanged="ddl_1_SelectedIndexChanged">
<asp:ListItem Value="first">选定第一项</asp:ListItem>
<asp:ListItem Value="second">选定第二项</asp:ListItem>
<asp:ListItem Value="third">选定第三项</asp:ListItem>
</asp:DropDownList>
<br /><br />
<span class="w250">获取选定项的selectedIndex:</span><asp:TextBox ID="txt_index" runat="server"></asp:TextBox>
<br />
<span class="w250">获取选定项的selectedText:</span><asp:TextBox ID="txt_text" runat="server"></asp:TextBox>
<br/>
<span class="w250">获取选定项的selectedValue:</span><asp:TextBox ID="txt_value" runat="server"></asp:TextBox>
<br />
<span class="w250">获取ddl中总共有多少个选项:</span><asp:TextBox ID="txt_ItemCount" runat="server"></asp:TextBox>
<br />
<br/>
<asp:Button ID="btn_clear" runat="server" Text="清除所有的项"
οnclick="btn_clear_Click" />
<asp:Button ID="btn_s3" runat="server" Text="自动选中第三项" οnclick="btn_s3_Click" />
</div>
<hr />
<div id="div_p2">
<p>让DropdownList也可以作为导航：</p>
<asp:DropDownList ID="ddl_nav" runat="server" DataSourceID="ADS_NAV"
DataTextField="网站名称" DataValueField="网址" >
</asp:DropDownList>
<asp:Button ID="Button1" runat="server" Text="go >" οnclick="Button1_Click" />
<asp:AccessDataSource ID="ADS_NAV" runat="server" DataFile="~/DATA/51ZXW.mdb"
SelectCommand="SELECT [网站名称], [网址] FROM [TB_HLINKS]"></asp:AccessDataSource>
<br />
<asp:Button ID="Button2" runat="server" Text="设置第三项的内容与网址，到google"
οnclick="Button2_Click" />
<br />
<asp:Button ID="Button3" runat="server" Text="给ddl_nav添加一个ListItem（对象）"
οnclick="Button3_Click" />
</div>
</div>
</form>
</body>
</html>
页面布局如下：
.aspx.cs代码如下：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
public partial class Sample_3_7 : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
}
protected void ddl_1_SelectedIndexChanged(object sender, EventArgs e)
{
txt_index.Text = ddl_1.SelectedIndex.ToString();
//注意获取text需要2个步骤：1 获取选定的Item; 2 获取Item的Text
txt_text.Text = ddl_1.SelectedItem.Text;
//也可以用更复杂的结构获取text（仅作为逻辑教学）
//txt_text.Text = ddl_1.Items[ddl_1.SelectedIndex].Text;
txt_value.Text = ddl_1.SelectedValue;
txt_ItemCount.Text = ddl_1.Items.Count.ToString();
}
//重定向
protected void Button1_Click(object sender, EventArgs e)
{
string url = ddl_nav.SelectedValue;
//请注意这个语句：重定向
Response.Redirect(url);
}
//清除所有项
protected void btn_clear_Click(object sender, EventArgs e)
{
ddl_1.Items.Clear();
}
protected void btn_s3_Click(object sender, EventArgs e)
{
//在设定之前，先要清除原先的选项，否则报错
ddl_1.SelectedItem.Selected = false;
//注意第三项的下标是2:
ddl_1.Items[2].Selected = true;
//Response.Write(ddl_1.GetType().ToString());
}
//手动修改一项google
protected void Button2_Click(object sender, EventArgs e)
{
ddl_nav.Items[2].Text = "GOOGLE";
ddl_nav.Items[2].Value = "http://";
}
//以面向对象的编程方式，给ddl_nav添加一个子项
protected void Button3_Click(object sender, EventArgs e)
{
ListItem obj_li;
obj_li = new ListItem(); //实例化obj_li，然后才可以对其进行操作
obj_li.Text = "新浪";
obj_li.Value = "http://";
//这句的形式非常重要：给某个对象 添加一个子对象
ddl_nav.Items.Add(obj_li);
}
}
浏览器中：
