Web.config文件假设有如下需要管理的配置信息: 

<appSettings>
    <add key="SiteTitle" value="站点名称" />
    <add key="SiteUrl" value="主页网址" />
    <add key="SiteLogo" value="站点Logo" />
    <add key="SiteBanner" value="站点Banner" />
    <add key="SiteEmail" value="联系Email" />
</appSettings>

实现的c#核心代码:

一、将Web.config中的相关信息读入TextBox

private void Page_Load(object sender, System.EventArgs e)
  {
   if(!Page.IsPostBack)
   {
    //将Web.config中的相关值填入TextBox
    this.txtTitle.Text=System.Configuration.ConfigurationSettings.AppSettings["SiteTitle"];
    this.txtUrl.Text=System.Configuration.ConfigurationSettings.AppSettings["SiteUrl"];
    this.txtLogo.Text=System.Configuration.ConfigurationSettings.AppSettings["SiteLogo"];
    this.txtBanner.Text=System.Configuration.ConfigurationSettings.AppSettings["SiteBanner"];
    this.txtEmail.Text=System.Configuration.ConfigurationSettings.AppSettings["SiteEmail"];
   }

  }

二、将修改后的内容写入Web.config

  private void btnSave_Click(object sender, System.EventArgs e)
  {
   string filename=Server.MapPath("web.config");
   string KeyName;//键名称

   XmlDocument  xmldoc= new XmlDocument();
   try
   {
    xmldoc.Load(filename);
   }
   catch
   {
    Response.Write("<script>alert('读文件时错误,请检查 Web.config 文件是否存在!')</script>");
    return;
   }
   
   XmlNodeList DocdNodeNameArr=xmldoc.DocumentElement.ChildNodes;//文档节点名称数组
   foreach(XmlElement DocXmlElement in DocdNodeNameArr)
   {
    if(DocXmlElement.Name.ToLower()=="appsettings")//找到名称为 appsettings 的节点
    {
     XmlNodeList KeyNameArr=DocXmlElement.ChildNodes;//子节点名称数组
     if ( KeyNameArr.Count >0 )
     {
      foreach(XmlElement xmlElement in KeyNameArr)
      {
       KeyName=xmlElement.Attributes["key"].InnerXml;//键值
       switch(KeyName)
       {
        case "SiteTitle":
         xmlElement.Attributes["value"].Value=this.txtTitle.Text;
         break;
        case "SiteUrl":
         xmlElement.Attributes["value"].Value=this.txtUrl.Text;
         break;
        case "SiteLogo":
         xmlElement.Attributes["value"].Value=this.txtLogo.Text;
         break;
        case "SiteBanner":
         xmlElement.Attributes["value"].Value=this.txtBanner.Text;
         break;
        case "SiteEmail":
         xmlElement.Attributes["value"].Value=this.txtEmail.Text;
         break;

       }
      }
     }
    }
   }
   try
   {
    xmldoc.Save(filename);
    Response.Write("<script>alert('OK,信息已保存!')</script>");
   }
   catch
   {
    Response.Write("<script>alert('写文件时错误,请检查 Web.config 文件是否存在!')</script>");
    return;
   }

  }