title: Flutter: Run method on Widget build complete
body: <p>I would like to be able to run functions once a Widget has finished building/loading but I am unsure how.</p>
  <p>My current use case is to check if a user is authenticated and if not, redirect to a login view. I do not want to check before and push either the login view or the main view, it needs to happen after the main view has loaded.</p>
  <p>Is there anything I can use to do this?</p>