title: How to display login screen only one time?
body: <p>I am creating a project where I have a login screen, which is used for user to login into the<br>
  Application. This login screen should only be visible the first time, so the user can fill it and log in, but when user opens the application at the second time the application must   show main.activity.   How to use <a href="http://developer.android.com/guide/topics/data/data-storage.html#pref" rel="noreferrer">Shared preference</a>.      </p>
  
  <p>I don't understand how to do this.      </p>