Example of GoRouter nested navigation using BottomNavigationBar

go_router_nested_navigation.dart

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

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

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

  static const title = 'GoRouter Example: Nested Navigation';

  @override
  Widget build(BuildContext context) => MaterialApp.router(
        routeInformationParser: _router.routeInformationParser,
        routerDelegate: _router.routerDelegate,
        title: title,
      );

  late final _router = GoRouter(
    routes: [
      GoRoute(
        path: '/',
        redirect: (_) => '/${Families.data[0].id}',
      ),
      GoRoute(
        path: '/:fid',
        name: 'family',
        builder: (context, state) => FamilyTabsScreen(
          key: state.pageKey,
          selectedFamily: Families.family(state.params['fid']!),
        ),
        routes: [
          GoRoute(
            path: ':pid',
            name: 'person',
            builder: (context, state) {
              final family = Families.family(state.params['fid']!);
              final person = family.person(state.params['pid']!);

              return PersonScreen(family: family, person: person);
            },
          ),
        ],
      ),
    ],

    // show the current router location as the user navigates page to page; note
    // that this is not required for nested navigation but it is useful to show
    // the location as it changes
    navigatorBuilder: (context, state, child) => Material(
      child: Column(
        children: [
          Expanded(child: child),
          Padding(
            padding: const EdgeInsets.all(8),
            child: Text(state.location),
          ),
        ],
      ),
    ),
  );
}

class FamilyTabsScreen extends StatefulWidget {
  FamilyTabsScreen({required Family selectedFamily, Key? key})
      : index = Families.data.indexWhere((f) => f.id == selectedFamily.id),
        super(key: key) {
    assert(index != -1);
  }

  final int index;

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

class _FamilyTabsScreenState extends State<FamilyTabsScreen> {
  @override
  void didUpdateWidget(FamilyTabsScreen oldWidget) {
    super.didUpdateWidget(oldWidget);
    setState(() => _selectedIndex = widget.index);
  }

  int _selectedIndex = 0;

  void _tap(BuildContext context, int index) {
    setState(() => _selectedIndex = index);
    context.go('/${Families.data[index].id}');
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      // Use this if you want the share the same AppBar across all tabs
      appBar: AppBar(title: Text(Families.data[_selectedIndex].name)),
      body: FeedPage(
        fid: Families.data[_selectedIndex].id,
      ),
      bottomNavigationBar: BottomNavigationBar(
        type: BottomNavigationBarType.fixed,
        unselectedItemColor: Colors.grey,
        selectedItemColor: Colors.blue,
        currentIndex: _selectedIndex,
        items: [
          for (final f in Families.data)
            BottomNavigationBarItem(
              icon: const Icon(
                Icons.layers,
              ),
              label: f.name,
            ),
        ],
        onTap: (index) => _tap(context, index),
      ),
    );
  }
}

class FamilyView extends StatefulWidget {
  const FamilyView({required this.family, Key? key}) : super(key: key);
  final Family family;

  @override
  State<FamilyView> createState() => _FamilyViewState();
}

/// Use the [AutomaticKeepAliveClientMixin] to keep the state, like scroll
/// position and text fields when switching tabs, as well as when popping back
/// from sub screens. To use the mixin override [wantKeepAlive] and call
/// `super.build(context)` in build.
///
/// In this example if you make a web build and make the browser window so low
/// that you have to scroll to see the last person on each family tab, you will
/// see that state is kept when you switch tabs and when you open a person
/// screen and pop back to the family.
class _FamilyViewState extends State<FamilyView>
    with AutomaticKeepAliveClientMixin {
  // Override `wantKeepAlive` when using `AutomaticKeepAliveClientMixin`.
  @override
  bool get wantKeepAlive => true;

  @override
  Widget build(BuildContext context) {
    // Call `super.build` when using `AutomaticKeepAliveClientMixin`.
    super.build(context);
    return ListView(
      children: [
        for (final p in widget.family.people)
          ListTile(
            title: Text(p.name),
            onTap: () => context.go('/${widget.family.id}/${p.id}'),
          ),
      ],
    );
  }
}

class PersonScreen extends StatelessWidget {
  const PersonScreen({required this.family, required this.person, Key? key})
      : super(key: key);

  final Family family;
  final Person person;

  @override
  Widget build(BuildContext context) => Scaffold(
        appBar: AppBar(title: Text(person.name)),
        body: Center(
            child: Column(
          children: [
            Text('${person.name} ${family.name} is ${person.age} years old'),
            ElevatedButton(
              style: ElevatedButton.styleFrom(
                primary: Colors.black, // background (button) color
                onPrimary: Colors.white, // foreground (text) color
              ),
              onPressed: () => context.goNamed('family', params: {
                'fid': 'journal',
              }),
              child: const Text('Go to Journal'),
            )
          ],
        )),
      );
}

class FeedPage extends StatelessWidget {
  const FeedPage({Key? key, required this.fid}) : super(key: key);
  final String fid;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      // Use this if you want each child page to have its own AppBar
      //appBar: AppBar(title: const Text('Feed')),
      body: Center(
        child: ElevatedButton(
          style: ElevatedButton.styleFrom(
            primary: Colors.black, // background (button) color
            onPrimary: Colors.white, // foreground (text) color
          ),
          onPressed: () => context.goNamed('person', params: {
            'fid': fid,
            'pid': 'p1',
          }),
          child: const Text('Detail'),
        ),
      ),
    );
  }
}

// DATA

class Person {
  Person({required this.id, required this.name, required this.age});

  final String id;
  final String name;
  final int age;
}

class Family {
  Family({required this.id, required this.name, required this.people});

  final String id;
  final String name;
  final List<Person> people;

  Person person(String pid) => people.singleWhere(
        (p) => p.id == pid,
        orElse: () => throw Exception('unknown person $pid for family $id'),
      );
}

class Families {
  static final data = [
    Family(
      id: 'feed',
      name: 'Sells',
      people: [
        Person(id: 'p1', name: 'Chris', age: 52),
        Person(id: 'p2', name: 'John', age: 27),
        Person(id: 'p3', name: 'Tom', age: 26),
      ],
    ),
    Family(
      id: 'journal',
      name: 'Addams',
      people: [
        Person(id: 'p1', name: 'Gomez', age: 55),
        Person(id: 'p2', name: 'Morticia', age: 50),
        Person(id: 'p3', name: 'Pugsley', age: 10),
        Person(id: 'p4', name: 'Wednesday', age: 17),
      ],
    ),
    Family(
      id: 'account',
      name: 'Hunting',
      people: [
        Person(id: 'p1', name: 'Mom', age: 54),
        Person(id: 'p2', name: 'Dad', age: 55),
        Person(id: 'p3', name: 'Will', age: 20),
        Person(id: 'p4', name: 'Marky', age: 21),
        Person(id: 'p5', name: 'Ricky', age: 22),
        Person(id: 'p6', name: 'Danny', age: 23),
        Person(id: 'p7', name: 'Terry', age: 24),
        Person(id: 'p8', name: 'Mikey', age: 25),
        Person(id: 'p9', name: 'Davey', age: 26),
        Person(id: 'p10', name: 'Timmy', age: 27),
        Person(id: 'p11', name: 'Tommy', age: 28),
        Person(id: 'p12', name: 'Joey', age: 29),
        Person(id: 'p13', name: 'Robby', age: 30),
        Person(id: 'p14', name: 'Johnny', age: 31),
        Person(id: 'p15', name: 'Brian', age: 32),
      ],
    ),
  ];

  static Family family(String fid) => data.family(fid);
}

extension on List<Family> {
  Family family(String fid) => singleWhere(
        (f) => f.id == fid,
        orElse: () => throw Exception('unknown family $fid'),
      );
}

I'll throw a huge wrench in... (which is what I've struggled with using GoRouter).

Now make it to where clicking the Detail button doesn't remove the tab bar from the screen.