how to keep bottom navigation bar in all pages with stateful widget in Flutter

I am able to navigate to multiple different pages with visible bottom navigation bar on all pages but not able to switch between all of them so how can I switch between tabs with bottom bar being there in all pages

I got till here using this Answer but not able to make it work i.e to switch between bottom navigation tabs...

in short I want to add view for my message tab i.e second tab and move to it also without losing my bottom navigation bar for every page i navigate to...

so far my code,

import 'package:flutter/material.dart';
void main() => runApp(MaterialApp(home: HomePage()));

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')));
}

Try like this:

class HomePage extends StatefulWidget {
  @override
  State<HomePage> createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  int activeIndex = 0;
  void changeActivePage(int index) {
    setState(() {
      activeIndex = index;
    });
  }

  List<Widget> pages = [];

  @override
  void initState() {
    pages = [
      Page1(() => changeActivePage(2)),
      Page2(),
      Page3(),
    ];
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        bottomNavigationBar: SizedBox(
          width: MediaQuery.of(context).size.width,
          child: Row(
            mainAxisAlignment: MainAxisAlignment.spaceEvenly,
            children: [
              IconButton(onPressed: () => changeActivePage(0), icon: Icon(Icons.call)),
              IconButton(onPressed: () => changeActivePage(1), icon: Icon(Icons.message)),
            ],
          ),
        ),
        body: pages[activeIndex]);
  }
}

// 1st Page:

class Page1 extends StatelessWidget {
  final Function callback;

  const Page1(this.callback);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Page1')),
      body: Center(
        child: RaisedButton(
          onPressed: () => callback(),
          child: Text('Go to Page3'),
        ),
      ),
    );
  }
}

// 2nd Page:

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

// 3rd Page:

class Page3 extends StatelessWidget {
  const Page3();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Page3')),
      body: Center(child: Text('Page3')),
    );
  }
}