title: android how to work with asynctasks progressdialog
body: <p>Asynctask have 4 override methods <code>onPreExecute()</code>, <code>doInBackground()</code>, <code>onProgressUpdate()</code>, <code>onPostExecute()</code>
  except <code>onProgressUpdate</code> all are working.
  What should I do so that onProgressUpdate() should work.
  Can anybody please briefly explain me what's the use of <code>onProgressUpdate()</code>, what should write within this?</p>