title: Making a custom dialog undismissable in android
body: <p>I have a custom dialog which have 2 progress bars and a button on it.
  I am showing this dialog in <code>onPreExecute ()</code>of an AsyncTask and dissmissng it <code>onPostExecute()</code>
  the problem is that when ever i touch screen during the operation the dialog dissmiss. I want it to only dismiss when cancel button on dialog is pressed or downloading files is complete.</p>