go_router_example.dart

import 'dart:async';

import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:go_router/go_router.dart';

void main() {
  runApp(const App());
}

class App extends StatefulWidget {
  const App({super.key});

  @override
  State<App> createState() => _AppState();
}

class _AppState extends State<App> {
  late final UserCubit _userCubit;
  late final GoRouter _goRouter;
  late final StreamSubscription<User?> _userSubscription;

  @override
  void initState() {
    super.initState();

    _userCubit = UserCubit(null);
    _goRouter = GoRouter(
      initialLocation: '/home',
      routes: [
        StatefulShellRoute.indexedStack(
          builder: (context, state, navigationShell) {
            return ScaffoldWithNavBar(
              navigationShell: navigationShell,
            );
          },
          branches: [
            StatefulShellBranch(
              routes: [
                GoRoute(
                  path: '/home',
                  builder: (context, state) => const Center(
                    child: Column(
                      mainAxisSize: MainAxisSize.min,
                      children: [
                        Text('Home'),
                        ProSwitch(),
                      ],
                    ),
                  ),
                ),
              ],
            ),
            StatefulShellBranch(
              routes: [
                GoRoute(
                  path: '/screen-a',
                  builder: (context, state) => const Center(
                    child: Column(
                      mainAxisSize: MainAxisSize.min,
                      children: [
                        Text('Screen A'),
                        ProSwitch(),
                      ],
                    ),
                  ),
                ),
              ],
            ),
            StatefulShellBranch(
              routes: [
                GoRoute(
                  path: '/pro',
                  redirect: (context, state) {
                    final isPremium = _userCubit.state?.isPremium ?? false;
                    if (!isPremium) {
                      return '/home';
                    }

                    return null;
                  },
                  builder: (context, state) => const Center(
                    child: Column(
                      mainAxisSize: MainAxisSize.min,
                      children: [
                        Text('Pro'),
                        ProSwitch(),
                      ],
                    ),
                  ),
                ),
              ],
            ),
          ],
        ),
      ],
    );

    _userSubscription = _userCubit.stream.listen((user) {
      _goRouter.refresh();
    });
  }

  @override
  void dispose() {
    _userSubscription.cancel();
    _userCubit.close();
    _goRouter.dispose();

    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return BlocProvider.value(
      value: _userCubit,
      child: MaterialApp.router(
        routerConfig: _goRouter,
      ),
    );
  }
}

class ScaffoldWithNavBar extends StatelessWidget {
  const ScaffoldWithNavBar({
    super.key,
    required this.navigationShell,
  });

  final StatefulNavigationShell navigationShell;

  @override
  Widget build(BuildContext context) {
    final userCubit = context.watch<UserCubit>();
    final isPremium = userCubit.state?.isPremium ?? false;

    return Scaffold(
      body: navigationShell,
      bottomNavigationBar: BottomNavigationBar(
        currentIndex: navigationShell.currentIndex,
        onTap: (value) {
          navigationShell.goBranch(value);
        },
        items: [
          const BottomNavigationBarItem(
            icon: Icon(Icons.home),
            label: 'Home',
          ),
          const BottomNavigationBarItem(
            icon: Icon(Icons.monitor),
            label: 'Screen A',
          ),
          if (isPremium)
            const BottomNavigationBarItem(
              icon: Icon(Icons.workspace_premium),
              label: 'Pro',
            ),
        ],
      ),
    );
  }
}

class ProSwitch extends StatelessWidget {
  const ProSwitch({super.key});

  @override
  Widget build(BuildContext context) {
    final userCubit = context.watch<UserCubit>();
    final isPremium = userCubit.state?.isPremium ?? false;

    return Switch.adaptive(
      value: isPremium,
      onChanged: (value) {
        userCubit.setUser(
          User(
            isPremium: value,
          ),
        );
      },
    );
  }
}

class UserCubit extends Cubit<User?> {
  UserCubit(super.initialState);

  void setUser(User? user) {
    emit(user);
  }
}

final class User {
  const User({
    required this.isPremium,
  });

  final bool isPremium;

  @override
  bool operator ==(Object other) {
    if (identical(this, other)) return true;

    return other is User && other.isPremium == isPremium;
  }

  @override
  int get hashCode {
    return Object.hashAll([
      isPremium,
    ]);
  }
}