Flutter: Keep BottomNavigationBar When Push to New Screen with Navigator

Screenshot:

---

Starting point:

void main() => runApp(MaterialApp(home: HomePage()));

HomePage [BottomNavigationBar + Page1]

class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      bottomNavigationBar: BottomNavigationBar(
        backgroundColor: Colors.orange,
        items: [
          BottomNavigationBarItem(icon: Icon(Icons.call), label: 'Call'),
          BottomNavigationBarItem(icon: Icon(Icons.message), label: 'Message'),
        ],
      ),
      body: Navigator(
        onGenerateRoute: (settings) {
          Widget page = Page1();
          if (settings.name == 'page2') page = Page2();
          return MaterialPageRoute(builder: (_) => page);
        },
      ),
    );
  }
}

1st Page:

class Page1 extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Page1')),
      body: Center(
        child: RaisedButton(
          onPressed: () => Navigator.pushNamed(context, 'page2'),
          child: Text('Go to Page2'),
        ),
      ),
    );
  }
}

2nd Page:

class Page2 extends StatelessWidget {
  @override
  Widget build(BuildContext context) => Scaffold(appBar: AppBar(title: Text('Page2')));
}