stack_index.dart

import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';

class Destination {
  const Destination(this.title, this.icon, this.color);
  final String title;
  final IconData icon;
  final MaterialColor color;
}

const List<Destination> allDestinations = <Destination>[
  Destination('Home', Icons.home, Colors.teal),
  Destination('Business', Icons.business, Colors.cyan),
  Destination('School', Icons.school, Colors.orange),
  Destination('Flight', Icons.flight, Colors.blue)
];


class DestinationView extends StatefulWidget {
  const DestinationView({ Key key, this.destination }) : super(key: key);

  final Destination destination;

  @override
  _DestinationViewState createState() => _DestinationViewState();
}

class _DestinationViewState extends State<DestinationView> {
  TextEditingController _textController;

  @override
  void initState() {
    super.initState();
    _textController = TextEditingController(
      text: 'sample text: ${widget.destination.title}',
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('${widget.destination.title} Text'),
        backgroundColor: widget.destination.color,
      ),
      backgroundColor: widget.destination.color[100],
      body: Container(
        padding: const EdgeInsets.all(32.0),
        alignment: Alignment.center,
        child: TextField(controller: _textController),
      ),
    );
  }

  @override
  void dispose() {
    _textController.dispose();
    super.dispose();
  }
}

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

class _HomePageState extends State<HomePage> with TickerProviderStateMixin<HomePage> {
  int _currentIndex = 0;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SafeArea(
        top: false,
        child: IndexedStack(
          index: _currentIndex,
          children: allDestinations.map<Widget>((Destination destination) {
            return DestinationView(destination: destination);
          }).toList(),
        ),
      ),
      bottomNavigationBar: BottomNavigationBar(
        currentIndex: _currentIndex,
        onTap: (int index) {
          setState(() {
            _currentIndex = index;
          });
        },
        items: allDestinations.map((Destination destination) {
          return BottomNavigationBarItem(
            icon: Icon(destination.icon),
            backgroundColor: destination.color,
            title: Text(destination.title)
          );
        }).toList(),
      ),
    );
  }
}

void main() {
  runApp(MaterialApp(home: HomePage(), debugShowCheckedModeBanner: false));
}

I wrote those samples for clarity, I wasn't trying to optimize performance. It is true that the list BottomNavigationBar items are rebuilt when the HomePage is rebuilt, and it would be nice to factor out a private widget that encapsulates the whole bottom navigation bar. That said, I'm not sure that there's a big performance benefit in doing that, at least in this case. You'd have to benchmark and see.

Hello, I'm trying your code, but I get this 3 errors:
line 20 :
error: The parameter 'key' can't have a value of 'null' because of its type, but the implicit default value is 'null'. (missing_default_value_for_parameter at [corvus] lib\main.dart:20)
error: The parameter 'destination' can't have a value of 'null' because of its type, but the implicit default value is 'null'. (missing_default_value_for_parameter at [corvus] lib\main.dart:20)
line 29 :
error: Non-nullable instance field '_textController' must be initialized. (not_initialized_non_nullable_instance_field at [corvus] lib\main.dart:29)
I think the last one can be solved using late keyword, but can you help me for the first 2?