Based on discussion @ https://github.com/csells/go_router/discussions/186

go_router_profile_example_with_nested_nav.dart

// ignore_for_file: constant_identifier_names

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

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

class MyApp extends StatelessWidget {
  MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp.router(
      routeInformationParser: _router.routeInformationParser,
      routerDelegate: _router.routerDelegate,
      title: 'Nested Navigation Example',
    );
  }

  late final _router = GoRouter(
    urlPathStrategy: UrlPathStrategy.path,
    routes: [
      GoRoute(
        path: '/',
        pageBuilder: (context, state) {
          return MaterialPage(
            key: state.pageKey,
            child: const HomePage(),
          );
        },
        routes: [
          GoRoute(
            path: 'profile',
            redirect: (_) => '/profile/home',
          ),
          GoRoute(
            path: 'profile/:section',
            pageBuilder: (context, state) {
              final section = profileSectionfromString(state.params['section']!);
              return MaterialPage(
                key: state.pageKey,
                child: ProfilePage(initialSection: section),
              );
            },
          ),
        ],
      ),
    ],
    errorPageBuilder: (context, state) {
      return MaterialPage(
        key: state.pageKey,
        child: ErrorPage(state.error),
      );
    },
  );
}

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Home Page'),
      ),
      body: Center(
        child: TextButton(
          onPressed: () {
            context.go('/profile');
          },
          child: Row(
            mainAxisAlignment: MainAxisAlignment.center,
            children: const [
              Icon(Icons.person),
              Text(' Profile'),
            ],
          ),
        ),
      ),
    );
  }
}

class ProfilePage extends StatefulWidget {
  final ProfileSections initialSection;
  const ProfilePage({
    Key? key,
    required this.initialSection,
  }) : super(key: key);

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

class _ProfilePageState extends State<ProfilePage> with SingleTickerProviderStateMixin {
  late final TabController _controller;
  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    _controller = TabController(
      length: ProfileSections.values.length,
      vsync: this,
      initialIndex: widget.initialSection.index,
    );
  }

  void _tap(int index) {
    context.go('/profile/${ProfileSections.values[index].asString().toLowerCase()}');
  }

  @override
  void didUpdateWidget(ProfilePage oldWidget) {
    super.didUpdateWidget(oldWidget);
    _controller.index = widget.initialSection.index;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Profile Page'),
        bottom: TabBar(
          controller: _controller,
          tabs: [for (final section in ProfileSections.values) Tab(text: section.asString())],
          onTap: (index) => _tap(index),
        ),
      ),
      body: TabBarView(
        controller: _controller,
        children: [
          for (final section in ProfileSections.values)
            Center(
              child: Text(section.asString()),
            )
        ],
      ),
    );
  }
}

enum ProfileSections {
  Home,
  Likes,
  Favourites,
  Following,
}

ProfileSections profileSectionfromString(String string) {
  return ProfileSections.values.firstWhere(
    (element) => describeEnum(element).toLowerCase() == string.toLowerCase(),
    orElse: () => ProfileSections.Home,
  );
}

extension on ProfileSections {
  String asString() => describeEnum(this);
}

/// sample error page
class ErrorPage extends StatelessWidget {
  const ErrorPage(this.error, {Key? key}) : super(key: key);
  final Exception? error;

  @override
  Widget build(BuildContext context) => Scaffold(
        appBar: AppBar(title: const Text('Page Not Found')),
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: [
              Text(error?.toString() ?? 'page not found'),
              TextButton(
                onPressed: () => context.go('/'),
                child: const Text('Home '),
              ),
            ],
          ),
        ),
      );
}