Asp. NET program to dynamically modify the setup items in Web.config (background CS code)

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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)
{
Open a file (assuming the web. Config in the root directory)
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);
}
}
}
}
}
}

private void Page_Init (object sender, EventArgs e)
{
InitializeComponent ();
}

#region Web Form Designer generated code
<summary>
Required to Designer support-do not modify
The contents is with the Code Editor.
</summary>
private void InitializeComponent ()
{
This. Button1.Click + = new System.EventHandler (this. Button1_Click);
This. Load + = new System.EventHandler (this. Page_Load);

}
#endregion

private void Button1_Click (object sender, System.EventArgs e)
{
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)
{
foreach (XmlElement el in _node)
{
if (el. attributes["Key"]. Innerxml.tolower () ==this. DropDownList1.SelectedItem.Value.ToLower ())
{
El. attributes["Value"]. Value=this. TextBox1.Text;
}
}
}
}
}
XmlDoc. Save (filename);
}
}
}