Flutter - Define/include/initialize/declare routes from different dart files

main.dart

// @author OMi Shah
// @email omi@codecyan.com
// @organization CodeCyan
// @website www.codecyan.com

import 'package:flutter/material.dart';

void main() {
  runApp(CodeCyanApp());
}

class CodeCyanApp extends StatelessWidget {
  // route 2
  final Map<String, WidgetBuilder> routes2 = {
    MyWidget2.id: (context) => MyWidget2(),
    MyWidget3.id: (context) => MyWidget3()
  };

  // route 3
  final Map<String, WidgetBuilder> routes3 = {
    MyWidget4.id: (context) => MyWidget2(),
    MyWidget5.id: (context) => MyWidget3()
  };

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      initialRoute: MyWidget.id,
      routes: {
        MyWidget.id: (context) => MyWidget(),
        MyWidget1.id: (context) => MyWidget1(),
        ...routes2,
        ...routes3,
      },
      debugShowCheckedModeBanner: false,
      home: Scaffold(body: MyWidget()),
    );
  }
}

class MyWidget extends StatelessWidget {
  static const id = "mywidget";

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(title: const Text("MyWidget")),
        body: Center(
            child: ElevatedButton(
                onPressed: () {
                  Navigator.pushNamed(context, MyWidget1.id);
                },
                child: const Text('Go to MyWidget1'))));
  }
}

class MyWidget1 extends StatelessWidget {
  static const id = "mywidget1";

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(title: const Text("MyWidget1")),
        body: Center(
            child: ElevatedButton(
                onPressed: () {
                  Navigator.pushNamed(context, MyWidget2.id);
                },
                child: const Text('Go to MyWidget2'))));
  }
}

class MyWidget2 extends StatelessWidget {
  static const id = "mywidget2";

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(title: const Text("MyWidget2")),
        body: Center(
            child: ElevatedButton(
                onPressed: () {
                  Navigator.pushNamed(context, MyWidget3.id);
                },
                child: const Text('Go to MyWidget3'))));
  }
}

class MyWidget3 extends StatelessWidget {
  static const id = "mywidget3";

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(title: const Text("MyWidget3")),
        body: Center(
            child: ElevatedButton(
                onPressed: () {
                  Navigator.pushNamed(context, MyWidget4.id);
                },
                child: const Text('Go to MyWidget4'))));
  }
}

class MyWidget4 extends StatelessWidget {
  static const id = "mywidget4";

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(title: const Text("MyWidget4")),
        body: Center(
            child: ElevatedButton(
                onPressed: () {
                  Navigator.pushNamed(context, MyWidget5.id);
                },
                child: const Text('Go to MyWidget5'))));
  }
}

class MyWidget5 extends StatelessWidget {
  static const id = "mywidget5";

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(title: const Text("MyWidget5")),
        body: Center(
            child: ElevatedButton(
                onPressed: () {
                  Navigator.pushNamed(context, MyWidget.id);
                },
                child: const Text('Go to MyWidget'))));
  }
}