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用Ajax.NET Ectention 实现的一个无刷新的多级动态下拉列表框，使用的3个UpdatePanel，每一个中放一个DropDownList，分别为
DropDownList1、2、2，其中UpdatePanel2由UpdatePanel1触发，UpdatePanel3由UpdatePanel2和UpdatePanel1共同触发，
也可以增加到很多级，只要类似的改代码就可以了。
以下为源代码
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>Untitled Page</title>
</head>
<body>
<form id="form1" runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server" />
<div style="float: left">
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
<asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True" Width="184px" OnSelectedIndexChanged="DropDownList1_SelectedIndexChanged" OnTextChanged="DropDownList1_SelectedIndexChanged" >
</asp:DropDownList>
</ContentTemplate>
</asp:UpdatePanel>
</div>
<div style="float: left">
<asp:UpdatePanel ID="UpdatePanel2" runat="server" UpdateMode="Conditional">
<ContentTemplate>
<asp:DropDownList ID="DropDownList2" runat="server" AutoPostBack="True" Width="168px" OnSelectedIndexChanged="DropDownList2_SelectedIndexChanged" >
</asp:DropDownList>
</ContentTemplate>
<Triggers>
<asp:AsyncPostBackTrigger ControlID="DropDownList1" EventName="SelectedIndexChanged" />
</Triggers>
</asp:UpdatePanel>
</div>
<asp:UpdatePanel ID="UpdatePanel3" runat="server">
<ContentTemplate>
<asp:DropDownList ID="DropDownList3" runat="server" AutoPostBack="True" Width="160px">
</asp:DropDownList>
</ContentTemplate>
<Triggers>
<asp:AsyncPostBackTrigger ControlID="DropDownList2" EventName="SelectedIndexChanged" />
<asp:AsyncPostBackTrigger ControlID="DropDownList1" EventName="SelectedIndexChanged" />
</Triggers>
</asp:UpdatePanel>
</form>
</body>
</html>
// Default.aspx.cs文件
using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Data.Sql;
using System.Data.SqlClient;
using System.Collections;
public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
DropDownList1.DataSource = CreateSource(0);
DropDownList1.DataTextField = "TypeName";
DropDownList1.DataValueField = "TypeID";
DropDownList1.DataBind();
int PreID = Convert.ToInt32(DropDownList1.SelectedValue);
DropDownList2.DataSource = CreateSource(PreID);
DropDownList2.DataTextField = "TypeName";
DropDownList2.DataValueField = "TypeID";
DropDownList2.DataBind();
PreID = Convert.ToInt32(DropDownList2.SelectedValue);
DropDownList3.DataSource = CreateSource(PreID);
DropDownList3.DataTextField = "TypeName";
DropDownList3.DataValueField = "TypeID";
DropDownList3.DataBind();
}
}
protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
int PreID = Convert.ToInt32(DropDownList1.SelectedValue);
if (CreateSource(PreID) != null)
{
DropDownList2.DataSource = CreateSource(PreID);
DropDownList2.DataTextField = "TypeName";
DropDownList2.DataValueField = "TypeID";
DropDownList2.DataBind();
PreID = Convert.ToInt32(DropDownList2.SelectedValue);
if (CreateSource(PreID) != null)
{
DropDownList3.DataSource = CreateSource(PreID);
DropDownList3.DataTextField = "TypeName";
DropDownList3.DataValueField = "TypeID";
DropDownList3.DataBind();
}
else
{
DropDownList3.Items.Clear();
}
}
else
{
DropDownList2.Items.Clear();
DropDownList3.Items.Clear();
}
}
protected void DropDownList2_SelectedIndexChanged(object sender, EventArgs e)
{
int PreID = Convert.ToInt32(DropDownList2.SelectedValue);
if (CreateSource(PreID) != null)
{
DropDownList3.DataSource = CreateSource(PreID);
DropDownList3.DataTextField = "TypeName";
DropDownList3.DataValueField = "TypeID";
DropDownList3.DataBind();
}
else
{
DropDownList3.Items.Clear();
}
}
protected ICollection CreateSource(int preId)
{
SqlConnection conn = new SqlConnection();
conn.ConnectionString = ConfigurationManager.ConnectionStrings["NewsReleaseConnectionString"].ConnectionString;
string sqlStr="Select TypeId,TypeName From ArticleType Where PreId=' "+preId.ToString()+"'";
SqlDataAdapter sda = new SqlDataAdapter(sqlStr,conn);
DataSet ds = new DataSet();
sda.Fill(ds);
if (ds.Tables[0].Rows.Count <= 0)
{
return null;
}
else
{
return ds.Tables[0].DefaultView;
}
}
}
数据库中的相应表的SQL
USE [NewsRelease]
GO
/****** 对象: Table [dbo].[ArticleType] 脚本日期: 12/05/2007 12:49:06 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
SET ANSI_PADDING ON
GO
CREATE TABLE [dbo].[ArticleType](
[TypeID] [bigint] IDENTITY(1,1) NOT FOR REPLICATION NOT NULL,
[TypeName] [varchar](20) COLLATE Chinese_PRC_CI_AS NOT NULL,
[PreID] [bigint] NOT NULL,
[AddTime] [datetime] NULL,
CONSTRAINT [PK_ArticleType] PRIMARY KEY CLUSTERED
(
[TypeID] ASC
)WITH (PAD_INDEX = OFF, IGNORE_DUP_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY]
GO
SET ANSI_PADDING OFF
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