public class AppLog
{
  private static string LogFileDir = Environment.GetFolderPath(Environment.SpecialFolder.CommonApplicationData) + @"\ApplicationLog";
  private static string LogFileName = @"\Applog.txt";
       
  public static void WriteMessage(string message)
  {
   if (!Directory.Exists(LogFileDir))
      Directory.CreateDirectory(LogFileDir);
  using (StreamWriter writer = new StreamWriter(LogFileDir + LogFileName, true))
   {
                writer.WriteLine(message);
     }

   }
  }