title: Android Firebase Persistence Set
body: <p>I'm currently developing a android project and I have a little problem. I'm using firebase for database and I'm saving datas offline to local storage but when I set <code>database.setPersistenceEnabled(true);</code> second time, my app crashes. How can I prevent that?
  I'm setting that just once in LoginActivity and I don't use that but my app is in the background and re-open the app my app crashes because of the persistence.
  And a little question too, after saving any data to firebase my activity re-opens. I don't understand that either. Can anyone help me?</p>