Generate dynamic initial route in Flutter

main.dart

import 'package:flutter/material.dart';

final Color darkBlue = Color.fromARGB(255, 18, 32, 47);

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return StreamBuilder(
        stream: null, //SOME FUNCTION HERE
        builder: (context, snapshot) {
          if (!snapshot.hasData) {
            return Material(
              child: Center(child: CircularProgressIndicator()),
            );
          }

          return MaterialApp(
            title: 'App',
            themeMode: ThemeMode.system,
            debugShowCheckedModeBanner: false,
            onGenerateInitialRoutes: (_) {
              if (snapshot.data) {
                return <Route>[
                  MaterialPageRoute(builder: (context) => HomePage())
                ];
              } else {
                return <Route>[
                  MaterialPageRoute(builder: (context) => IntroPage())
                ];
              }
            },
            onGenerateRoute: Routes.generateRoute,
            localeResolutionCallback:
                (Locale locale, Iterable<Locale> supportedLocales) {
              return locale;
            },
          );
        });
  }
}

class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Text('Hello, World! Home', style: Theme.of(context).textTheme.headline4);
  }
}

class IntroPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Text('Hello, World! Intro', style: Theme.of(context).textTheme.headline4);
  }
}

//Route generator (Navigation Route 1.0)
class Routes {
  static Route<dynamic> generateRoute(RouteSettings settings) {
    switch (settings.name) {
      case '/':
        return MaterialPageRoute(builder: (_) => IntroPage());
      case '/homePage':
        return MaterialPageRoute(builder: (_) => HomePage());
      default:
        return MaterialPageRoute(
            builder: (_) => Scaffold(
                  body: Center(
                      child: Text('No route defined for ${settings.name}')),
                ));
    }
  }
}