Flutter: pass Arguments as a Route

main.dart

//FILE main.dart
import 'package:flutter/material.dart';
//import 'routes.dart'

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
        title: 'Material App',
        initialRoute: 'home',
        routes: myRoutes,
        onGenerateRoute: (settings) => generatedRoutes(settings));
  }
}

class HomePage extends StatefulWidget {
  const HomePage({Key key}) : super(key: key);
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            RaisedButton(
              onPressed: () {
                Navigator.pushNamed(context, 'otherPage',
                    arguments: OtherPageArguments('Hello World', 2));
              },
              child: const Text('Go to Page with Arguments'),
            ),
            const SizedBox(height: 32),
            RaisedButton(
              onPressed: () {
                Navigator.pushNamed(context, 'helpPage');
              },
              child: const Text('Go to Page without Arguments'),
            ),
          ],
        ),
      ),
    );
  }
}

///FILE routes.dart MOVE THE BELOW CODE TO ANOTHER FILE

//import 'pages.dart'
//When routes doesn't have arguments goes here, 
Map<String, WidgetBuilder> get myRoutes => <String, WidgetBuilder>{
      'home': (context) => const HomePage(),
      'helpPage': (context) => const HelpPage(),
    };

//When routes have arguments goes here, if the route has more than 1 argument, need to pass those inside 1 class as argument.
Route<dynamic> generatedRoutes(RouteSettings settings) {
  switch (settings.name) {
    case 'otherPage':
      final args = settings.arguments as OtherPageArguments;
      return MaterialPageRoute(
        builder: (context) {
          return OtherPage(
            name: args.name,
            quantity: args.quantity,
          );
        },
      );
      break;
    default:
      return null;
  }
}

class OtherPageArguments {
  String name;
  int quantity;
  OtherPageArguments(this.name, this.quantity);
}

//FILE pages.dart MOVE THE BELOW CODE TO ANOTHER FILE
///import 'routes.dart'
class HelpPage extends StatefulWidget {
  const HelpPage({Key key}) : super(key: key);
  @override
  _HelpPageState createState() => _HelpPageState();
}

class _HelpPageState extends State<HelpPage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: const Text('No arguments'),
        ),
        body: Container());
  }
}

class OtherPage extends StatefulWidget {
  final String name;
  final int quantity;
  const OtherPage({@required this.name, @required this.quantity, Key key})
      : super(key: key);
  @override
  _OtherPageState createState() => _OtherPageState();
}

class _OtherPageState extends State<OtherPage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text(widget.name)),
      body: Center(
        child: Text('${widget.name} & ${widget.quantity}'),
      ),
    );
  }
}