ConfigurationManager.RefreshSection Method

// Create the AppSettings section.
// The function uses the GetSection(string)method 
// to access the configuration section. 
// It also adds a new element to the section collection.
public static void CreateAppSettings()
{
  // Get the application configuration file.
  System.Configuration.Configuration config =
    ConfigurationManager.OpenExeConfiguration(
          ConfigurationUserLevel.None);

  string sectionName = "appSettings";

  // Add an entry to appSettings.
  int appStgCnt =
      ConfigurationManager.AppSettings.Count;
  string newKey = "NewKey" + appStgCnt.ToString();

  string newValue = DateTime.Now.ToLongDateString() + 
    " " + DateTime.Now.ToLongTimeString();

  config.AppSettings.Settings.Add(newKey, newValue);

  // Save the configuration file.
  config.Save(ConfigurationSaveMode.Modified);

  // Force a reload of the changed section. This 
  // makes the new values available for reading.
  ConfigurationManager.RefreshSection(sectionName);

  // Get the AppSettings section.
  AppSettingsSection appSettingSection =
    (AppSettingsSection)config.GetSection(sectionName);

  Console.WriteLine();
  Console.WriteLine("Using GetSection(string).");
  Console.WriteLine("AppSettings section:");
  Console.WriteLine(
    appSettingSection.SectionInformation.GetRawXml());
}