title: How to have one Scaffold with one BottomNavigationBar and multiple MaterialApp.routes
body: <p>By looking at the Material Design document about <a href="https://material.io/components/bottom-navigation#behavior" rel="nofollow noreferrer">Bottom Navigation</a> I can see multiple pages with nice transitions that use only one BottomNavigationBar, and probably one Scaffold.</p>
  <p>I would like to replicate this but I struggle to do so, and previous answers lead to wrong solutions with bad animation and multiple Scaffold.</p>
  <p>I want, one MaterialApp with multiple routes and one scaffold with one bottom bar. By tapping the bar items, I want to change the routes and so, the page and keep the actual bottom bar.</p>
  <p>What is good the practice to implement this?</p>