code: @Override
      public void setSession(Session newSession) {
          super.setSession(newSession);
          if (loginButton != null) {
              loginButton.setSession(newSession);
          }
          fetchUserInfo();
          updateUI();
      }
docs: Set the Session object to use instead of the active Session. Since a Session
  cannot be reused, if the user logs out from this Session, and tries to
  log in again, a new Active Session will be used instead.
  <p/>
  If the passed in session is currently opened, this method will also attempt to
  load some user information for display (if needed).
  
  @param newSession the Session object to use
  @throws com.facebook.FacebookException if errors occur during the loading of user information