named routes with args

main.dart

// onGenerateRoute callback navigation

import 'package:flutter/material.dart';

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

class App extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Routing demo (onGenerateRoute)',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      initialRoute: '/',
      onGenerateRoute: (RouteSettings settings) {
        switch (settings?.name) {
          case '/page_2':
            return MaterialPageRoute(builder: (context) => PageTwo(settings?.arguments));
          case '/page_3':
            return MaterialPageRoute(builder: (context) => PageThree(settings?.arguments));
          case '/':
          default:
            return MaterialPageRoute(builder: (context) => RootPage());
        }
      },
    );
  }
}

// Page 1
class RootPage extends StatefulWidget {  
  RootPage({Key key}) : super(key: key);

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

class _RootPageState extends State<RootPage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Root Page'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text('Root Page'),
            RaisedButton(
                child: Text('page 2'),
                onPressed: () => Navigator.of(context).pushNamed('/page_2', arguments: {'from': 'root page'})),
            RaisedButton(
                child: Text('page 3'),
                onPressed: () => Navigator.of(context).pushNamed('/page_3', arguments: {'from': 'root page'})),
          ],
        ),
      ),
    );
  }
}

// Page 2
class PageTwo extends StatefulWidget {  
  final args;
  
  PageTwo(this.args, {Key key}) : super(key: key);

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

class _PageTwoState extends State<PageTwo> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Page #2'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text('Page #2, navigated from: ${widget.args['from']}'),
            RaisedButton(
                child: Text('root page'),
                onPressed: () => Navigator.of(context).pushNamed('/')),
            RaisedButton(
                child: Text('page 3'),
                onPressed: () => Navigator.of(context).pushNamed('/page_3', arguments: {'from': 'page 2'})),
          ],
        ),
      ),
    );
  }
}

// Page 3
class PageThree extends StatefulWidget {  
  final args;

  PageThree(this.args, {Key key}) : super(key: key);

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

class _PageThreeState extends State<PageThree> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Page #3'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text('Page #3, navigated from: ${widget.args['from']}'),
            RaisedButton(
                child: Text('root page'),
                onPressed: () => Navigator.of(context).pushNamed('/')),
            RaisedButton(
                child: Text('page 2'),
                onPressed: () => Navigator.of(context).pushNamed('/page_2', arguments: {'from': 'page 3'})),
          ],
        ),
      ),
    );
  }
}