c# 动态修改app.config文件

public class AppConfig
{ 
     private XmlDocument Doc=new XmlDocument();
     private AppDomain Ad = AppDomain.CurrentDomain;
     public AppConfig()
         {
               Doc.Load(Ad.SetupInformation.ConfigurationFile); 
          }
     public void LoadAppConfig()
         {
               Doc.Load(Ad.SetupInformation.ConfigurationFile);
         }
     public void SetAppValue(string key,string newValue)
        {
               Doc.SelectSingleNode("/configuration/appSettings/add[@key='"+key+"']").Attributes["value"].Value = newValue; 
        }  
     public void SaveAppConfig() 
        {
              Doc.Save(Ad.SetupInformation.ConfigurationFile);
              Doc.Load(Ad.SetupInformation.ConfigurationFile); 
        }
     public string GetAppValue(string key)
        {
              return Doc.SelectSingleNode("/configuration/appSettings/add[@key='" + key + "']").Attributes["value"].Value;
        } 
}