来篇文章：ASP。NET程序中动态修改web.config中的设置项目 （后台CS代码）

朋友们可以自行测试，我这里都没有问题了，鳖了一上午的问题总算解决了
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.Xml ;
namespace WebApplication1
{
/// <summary>
/// Summary description for WebForm1.
/// </summary>
public class WebForm1 : System.Web.UI.Page
{
protected System.Web.UI.WebControls.TextBox TextBox1;
protected System.Web.UI.WebControls.DropDownList DropDownList1;
protected System.Web.UI.WebControls.Button Button1;
public WebForm1()
{
Page.Init += new System.EventHandler(Page_Init);
}
private void Page_Load(object sender, System.EventArgs e)
{
if(!Page.IsPostBack)
{
//打开某文件(假设WEB。CONFIG在根目录中)
string filename=Server.MapPath("/") + @"web.config";
XmlDocument    xmldoc= new XmlDocument();
xmldoc.Load(filename);
XmlNodeList topM=xmldoc.DocumentElement.ChildNodes;
foreach(XmlElement element in topM)
{
if(element.Name.ToLower()=="appsettings")
{
XmlNodeList _node=element.ChildNodes;
if ( _node.Count >0 )
{
DropDownList1.Items.Clear();
foreach(XmlElement el in _node)
{
DropDownList1.Items.Add(el.Attributes["key"].InnerXml);
}
}
}
}
}