删除和添加web.config属性

using System;
using System.Xml;
using System.Configuration;
using System.Collections;
using System.Reflection;
using System.Diagnostics ;
public enum   ConfigFileType
{
WebConfig ,
AppConfig
}
public class AppConfig : System.Configuration.AppSettingsReader
{
public string  docName = String.Empty;
private  XmlNode node=null;
private int _configType;
 public   int ConfigType
{
get
{
return _configType;
}
set
{
_configType=value;
}
}
public bool SetValue(string key, string value)
{
XmlDocument cfgDoc = new XmlDocument();
loadConfigDoc(cfgDoc);
// retrieve the appSettings node 
node =  cfgDoc.SelectSingleNode("//appSettings");
if( node == null )
{
throw new System.InvalidOperationException( "appSettings section not found");
}
try
{
// XPath select setting "add" element that contains this key    
XmlElement addElem= (XmlElement)node.SelectSingleNode("//add[@key='" +key +"']") ;
if (addElem!=null)
{
addElem.SetAttribute("value",value);
}
// not found, so we need to add the element, key and value
else
{
XmlElement entry = cfgDoc.CreateElement("add");
entry.SetAttribute("key",key);
entry.SetAttribute("value",value);
node.AppendChild(entry);
}
//save it
saveConfigDoc(cfgDoc,docName);
return true;
}
catch
{
return false;
}
}
private void saveConfigDoc(XmlDocument cfgDoc,string cfgDocPath)
{
try
{
XmlTextWriter writer = new XmlTextWriter( cfgDocPath , null );
writer.Formatting = Formatting.Indented;
cfgDoc.WriteTo( writer );
writer.Flush();
writer.Close();
return;
}
catch
{
throw;
}
}
public bool removeElement ( string elementKey)
{
try
{
XmlDocument cfgDoc = new XmlDocument();
loadConfigDoc(cfgDoc);
// retrieve the appSettings node 
node =  cfgDoc.SelectSingleNode("//appSettings");
if( node == null )
{
throw new System.InvalidOperationException( "appSettings section not found");
}
// XPath select setting "add" element that contains this key to remove   
node.RemoveChild( node.SelectSingleNode("//add[@key='" +elementKey +"']") );
saveConfigDoc(cfgDoc,docName);
return true;
}
catch
{
return false;
}
}
private XmlDocument loadConfigDoc( XmlDocument cfgDoc )
{
// load the config file 
if(  Convert.ToInt32(ConfigType)==Convert.ToInt32(ConfigFileType.AppConfig))
{
docName= ((Assembly.GetEntryAssembly()).GetName()).Name;
docName +=   ".exe.config";
}
else
{
docName=System.Web.HttpContext.Current.Server.MapPath("web.config");
}
cfgDoc.Load( docName );
return cfgDoc;
}
}