使用服务中的AsyncTask更新通知栏中的进度条？

I'm trying to download multiple binary files using a Service which contains an AsynTask for doing background work. I'm able to run the Service successfully, I've registered it in the Manifest file. I'm able to download the files, however I would like to show a progress bar in the notification bar. I am creating the Notification bar inside the onPreExecute() method and setting the progressbar and notifying the NotifactionManager inside the onProgressUpdate() method.I'm trying to download multiple binary files us