Setting conditional rootpage

Ionic Framework ionic-v3
1

Hi Guys,
I am trying to set Rootpage in this manner
Its working, but when navigating it shows error saying “nav Controller was destroyed” or "inserted view was already destroyed."
Can anyone please help me in this?
I am relatively new to ionic, only 1 month experince, so please go easy on me. :smiley:

this.storage.get('hasSeenTutorial')
      .then((hasSeenTutorial) =>
 {
        if (hasSeenTutorial) 
       {
          afAuth.authState.subscribe(auth => 
         {
            if(auth)
            {
              this.rootPage = 'TabsPage';
              toaster.setMessage('Has Seen Tutorial YES Auth');
              toaster.present();
            }
            else
            {
              this.rootPage = 'LoginPage';
              toaster.setMessage('Has Seen Tutorial NOT Auth');
              toaster.present();
            }
        });
      } 
    else
      {
          this.rootPage = 'TutorialPage';
          toaster.setMessage('Has NOT Seen Tutorial');
          toaster.present();
      }
}