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));
}

Quick question on performance: do code lines 89 to 84 imply that you are rebuilding those static BarItem widgets every time the parent widget _HomePageState rebuilds?
I see from your article that the bottom bar changes with every time the Destination changes but wondering if the BottomNavigationBarItems are themselves rebuilt every time.
If so, would we not want to reduce that as it is a performance anti pattern? (referencing - https://iiro.dev/2018/12/11/splitting-widgets-to-methods-performance-antipattern/)
If I've understood wrongly, please let me know and help me understand what it is I am not getting right.
Thank you very much in advance.

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?