在程序运行时怎样修改App.config文件的数据库配置节??????????????????急....在线等
<connectionStrings>  
                          <add   name= "conString "   connectionString= "Database=newsinco;Server=192.168.0.66;uid=sa;pwd=aaa;Connection   Reset=FALSE " 
                                     providerName= "System.Data.SqlClient "   />  
              </connectionStrings>  
 我知道是用下面的那个类,但具体不知道怎么用?求高手帮忙,真的很急,今天下午老大要我搞定,晕,具体怎要显示以前的,和怎样去修改, 
                                     Configuration   config=ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None); 
------解决方案--------------------       (前台页面代码) 
  <%@ Page language= "c# " Codebehind= "WebForm1.aspx.cs " AutoEventWireup= "false " Inherits= "WebApplication1.WebForm1 " %>  
  <!DOCTYPE HTML PUBLIC  "-//W3C//DTD HTML 4.0 Transitional//EN " >  
  <HTML>  
  <HEAD>  
  <meta name= "GENERATOR " Content= "Microsoft Visual Studio 7.0 ">  
  <meta name= "CODE_LANGUAGE " Content= "C# ">  
  <meta name= "vs_defaultClientScript " content= "JavaScript (ECMAScript) ">  
  <meta name= "vs_targetSchema " content= "http://schemas.microsoft.com/intellisense/ie5 ">  
  </HEAD>  
  <body MS_POSITIONING= "GridLayout ">  
  <form id= "Form1 " method= "post " runat= "server ">  
  <FONT face= "宋体 ">  
  <asp:TextBox id= "TextBox1 " style= "Z-INDEX: 101; LEFT: 164px; POSITION: absolute; TOP: 190px " runat= "server " Width= "204px " Height= "25px ">  </asp:TextBox>  
  <asp:Button id= "Button1 " style= "Z-INDEX: 102; LEFT: 386px; POSITION: absolute; TOP: 188px " runat= "server " Width= "78px " Height= "25px " Text= "Button ">  </asp:Button>  
  <asp:DropDownList id= "DropDownList1 " style= "Z-INDEX: 103; LEFT: 29px; POSITION: absolute; TOP: 192px " runat= "server " Width= "130px " Height= "22px ">  </asp:DropDownList>  
  </FONT>  
  </form>  
  </body>  
  </HTML>    
 (后台CS代码) 
 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 ")