title: navigating to a TabBar from different ViewControllers
body: <p>I am trying to build an app that has a landing screen with a link to either "signin" page or "sign up" page. The meat of the app is a tabbar. Where would be the right place to implement the tabbarcontroller given that a user can have the following flow:</p>
  
  <ol>
  <li>landing page - >sign in -> main app</li>
  <li>landing page - > sign up -> main app</li>
  <li>straight to main app if the user logged in already</li>
  </ol>
  
  <p>Is it possible to do that in the AppDelegate? But then, how do I go back to the appDelegate if I am at the "sign in"/"sign up" page?</p>
  
  <p>Thanks so much for the help!!</p>