Replace navigation_and_routing with a new sample (#832)

* move snippets into old_snippets directory

* add new navigation_and_routing sample

* add copyright headers

* Apply #827 to old_snippets/ directory and upgrade them to null safety

* Code review comments

- Move Guard class into parser.dart
- Move usage of guards from Delegate to RouteInformationParser
- Rename delegate to SimpleRouterDelegate

* clean up imports

* refactor settings screen, fix bug

* avoid conflicting paths /books/new and /books/1 - rename to book/1

* dispose fields in _BookstoreState class

* remove /books path

This was causing problems

* add comment

* Change BookstoreAuthScope and BookstoreAuthScope to InheritedNotifier

* fix warnings

* Make the initial route configurable, set to '/signin'

* Enable deep linking

https://flutter.dev/docs/development/ui/navigation/deep-linking

* use path URL strategy on the web.

* remove TODO, add comment

navigation_and_routing/lib/src/app.dart

@@ -0,0 +1,101 @@
+// Copyright 2021, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+
+import 'auth.dart';
+import 'data.dart';
+import 'routing.dart';
+import 'screens/navigator.dart';
+import 'widgets/library_scope.dart';
+
+class Bookstore extends StatefulWidget {
+  const Bookstore({Key? key}) : super(key: key);
+
+  @override
+  _BookstoreState createState() => _BookstoreState();
+}
+
+class _BookstoreState extends State<Bookstore> {
+  final auth = BookstoreAuth();
+  late final BookstoreRouteGuard guard;
+  late final RouteState routeState;
+  late final SimpleRouterDelegate routerDelegate;
+  late final TemplateRouteParser routeParser;
+  final GlobalKey<NavigatorState> navigatorKey = GlobalKey<NavigatorState>();
+
+  final library = Library()
+    ..addBook('Left Hand of Darkness', 'Ursula K. Le Guin', true, true)
+    ..addBook('Too Like the Lightning', 'Ada Palmer', false, true)
+    ..addBook('Kindred', 'Octavia E. Butler', true, false)
+    ..addBook('The Lathe of Heaven', 'Ursula K. Le Guin', false, false);
+
+  @override
+  void initState() {
+    guard = BookstoreRouteGuard(auth: auth);
+
+    /// Configure the parser with all of the app's allowed path templates.
+    routeParser = TemplateRouteParser(
+      [
+        '/signin',
+        '/authors',
+        '/settings',
+        '/books/new',
+        '/books/all',
+        '/books/popular',
+        '/book/:bookId',
+        '/author/:authorId',
+      ],
+      guard: guard,
+      initialRoute: '/signin',
+    );
+
+    routeState = RouteState(routeParser);
+
+    routerDelegate = SimpleRouterDelegate(
+      routeState: routeState,
+      navigatorKey: navigatorKey,
+      builder: (context) => BookstoreNavigator(
+        navigatorKey: navigatorKey,
+        auth: auth,
+      ),
+    );
+
+    // Listen for when the user logs out and display the signin screen.
+    auth.addListener(_handleAuthStateChanged);
+
+    super.initState();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return RouteStateScope(
+      notifier: routeState,
+      child: BookstoreAuthScope(
+        notifier: auth,
+        child: LibraryScope(
+          library: library,
+          child: MaterialApp.router(
+            routerDelegate: routerDelegate,
+            routeInformationParser: routeParser,
+          ),
+        ),
+      ),
+    );
+  }
+
+  Future<void> _handleAuthStateChanged() async {
+    if (!auth.signedIn) {
+      routeState.go('/signin');
+    }
+  }
+
+  @override
+  void dispose() {
+    auth.removeListener(_handleAuthStateChanged);
+    routeState.dispose();
+    routerDelegate.dispose();
+    super.dispose();
+  }
+}

navigation_and_routing/lib/src/auth.dart

@@ -0,0 +1,2 @@
+export 'auth/auth.dart';
+export 'auth/auth_guard.dart';

navigation_and_routing/lib/src/auth/auth.dart

@@ -0,0 +1,53 @@
+// Copyright 2021, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter/widgets.dart';
+
+/// A mock authentication service
+class BookstoreAuth extends ChangeNotifier {
+  bool _signedIn = false;
+
+  bool get signedIn {
+    return _signedIn;
+  }
+
+  Future<void> signOut() async {
+    await Future<void>.delayed(const Duration(milliseconds: 200));
+    // Sign out.
+    _signedIn = false;
+    notifyListeners();
+  }
+
+  Future<bool> signIn(String username, String password) async {
+    await Future<void>.delayed(const Duration(milliseconds: 200));
+
+    // Sign in. Allow any password.
+    _signedIn = true;
+    notifyListeners();
+    return _signedIn;
+  }
+
+  @override
+  bool operator ==(Object other) {
+    return other is BookstoreAuth && other._signedIn == _signedIn;
+  }
+
+  @override
+  int get hashCode => _signedIn.hashCode;
+}
+
+class BookstoreAuthScope extends InheritedNotifier<BookstoreAuth> {
+  const BookstoreAuthScope({
+    required BookstoreAuth notifier,
+    required Widget child,
+    Key? key,
+  }) : super(key: key, notifier: notifier, child: child);
+
+  static BookstoreAuth? of(BuildContext context) {
+    return context
+        .dependOnInheritedWidgetOfExactType<BookstoreAuthScope>()
+        ?.notifier;
+  }
+}

navigation_and_routing/lib/src/auth/auth_guard.dart

@@ -0,0 +1,32 @@
+// Copyright 2021, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import '../routing.dart';
+import 'auth.dart';
+
+/// An implementation of [RouteGuard] that redirects to /signIn
+class BookstoreRouteGuard implements RouteGuard<ParsedRoute> {
+  BookstoreAuth auth;
+
+  BookstoreRouteGuard({
+    required this.auth,
+  });
+
+  /// Redirect to /signin if the user isn't signed in.
+  @override
+  Future<ParsedRoute> redirect(ParsedRoute from) async {
+    final signedIn = auth.signedIn;
+    final signInRoute = ParsedRoute('/signin', '/signin', {}, {});
+
+    // Go to /signin if the user is not signed in
+    if (!signedIn && from != signInRoute) {
+      return signInRoute;
+    }
+    // Go to /books if the user is signed in and tries to go to /signin.
+    else if (signedIn && from == signInRoute) {
+      return ParsedRoute('/books/popular', '/books/popular', {}, {});
+    }
+    return from;
+  }
+}

navigation_and_routing/lib/src/data.dart

@@ -0,0 +1,3 @@
+export 'data/author.dart';
+export 'data/book.dart';
+export 'data/library.dart';

navigation_and_routing/lib/src/data/author.dart

@@ -0,0 +1,13 @@
+// Copyright 2021, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'book.dart';
+
+class Author {
+  final int id;
+  final String name;
+  final List<Book> books;
+
+  Author(this.id, this.name, this.books);
+}

navigation_and_routing/lib/src/data/book.dart

@@ -0,0 +1,15 @@
+// Copyright 2021, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'author.dart';
+
+class Book {
+  final int id;
+  final String title;
+  late final Author author;
+  final bool isPopular;
+  final bool isNew;
+
+  Book(this.id, this.title, this.isPopular, this.isNew);
+}

navigation_and_routing/lib/src/data/library.dart

@@ -0,0 +1,41 @@
+// Copyright 2021, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:collection/collection.dart';
+
+import 'author.dart';
+import 'book.dart';
+
+class Library {
+  final List<Book> allBooks = [];
+  final List<Author> allAuthors = [];
+
+  void addBook(String title, String authorName, bool isPopular, bool isNew) {
+    var author =
+        allAuthors.firstWhereOrNull((author) => author.name == authorName);
+    var book = Book(allBooks.length, title, isPopular, isNew);
+
+    if (author == null) {
+      author = Author(allAuthors.length, authorName, [book]);
+      allAuthors.add(author);
+    } else {
+      author.books.add(book);
+    }
+
+    book.author = author;
+    allBooks.add(book);
+  }
+
+  List<Book> get popularBooks {
+    return [
+      ...allBooks.where((book) => book.isPopular),
+    ];
+  }
+
+  List<Book> get newBooks {
+    return [
+      ...allBooks.where((book) => book.isNew),
+    ];
+  }
+}

navigation_and_routing/lib/src/routing.dart

@@ -0,0 +1,4 @@
+export 'routing/delegate.dart';
+export 'routing/parsed_route.dart';
+export 'routing/parser.dart';
+export 'routing/route_state.dart';

navigation_and_routing/lib/src/routing/delegate.dart

@@ -0,0 +1,52 @@
+// Copyright 2021, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter/widgets.dart';
+
+import 'parsed_route.dart';
+import 'route_state.dart';
+
+class SimpleRouterDelegate extends RouterDelegate<ParsedRoute>
+    with ChangeNotifier, PopNavigatorRouterDelegateMixin<ParsedRoute> {
+  final RouteState routeState;
+  final WidgetBuilder builder;
+
+  @override
+  final GlobalKey<NavigatorState> navigatorKey;
+
+  SimpleRouterDelegate({
+    required this.routeState,
+    required this.builder,
+    required this.navigatorKey,
+    // ignore: prefer_initializing_formals
+  }) {
+    routeState.addListener(notifyListeners);
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return builder(context);
+  }
+
+  @override
+  Future<void> setNewRoutePath(ParsedRoute configuration) async {
+    routeState.route = configuration;
+    return SynchronousFuture(null);
+  }
+
+  @override
+  ParsedRoute get currentConfiguration {
+    return routeState.route;
+  }
+
+  @override
+  void dispose() {
+    routeState.removeListener(notifyListeners);
+    routeState.dispose();
+    super.dispose();
+  }
+}

navigation_and_routing/lib/src/routing/parsed_route.dart

@@ -0,0 +1,45 @@
+// Copyright 2021, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:collection/collection.dart';
+import 'package:quiver/core.dart';
+
+import 'parser.dart';
+
+/// A route path that has been parsed by [TemplateRouteParser].
+class ParsedRoute {
+  final String path;
+  final String pathTemplate;
+  final Map<String, String> parameters;
+  final Map<String, String> queryParameters;
+
+  static const _mapEquality = MapEquality<String, String>();
+
+  ParsedRoute(
+      this.path, this.pathTemplate, this.parameters, this.queryParameters);
+
+  @override
+  bool operator ==(Object other) {
+    return other is ParsedRoute &&
+        other.pathTemplate == pathTemplate &&
+        other.path == path &&
+        _mapEquality.equals(parameters, other.parameters) &&
+        _mapEquality.equals(queryParameters, other.queryParameters);
+  }
+
+  @override
+  int get hashCode => hash4(
+        path,
+        pathTemplate,
+        _mapEquality.hash(parameters),
+        _mapEquality.hash(queryParameters),
+      );
+
+  @override
+  String toString() => '<ParsedRoute '
+      'template: $pathTemplate '
+      'path: $path '
+      'parameters: $parameters '
+      'query parameters: $queryParameters>';
+}

navigation_and_routing/lib/src/routing/parser.dart

@@ -0,0 +1,68 @@
+// Copyright 2021, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:flutter/widgets.dart';
+import 'package:path_to_regexp/path_to_regexp.dart';
+
+import 'parsed_route.dart';
+
+abstract class RouteGuard<T> {
+  Future<T> redirect(T from);
+}
+
+/// Parses the URI path into a [ParsedRoute].
+class TemplateRouteParser extends RouteInformationParser<ParsedRoute> {
+  final List<String> _pathTemplates = [];
+  RouteGuard<ParsedRoute>? guard;
+  final ParsedRoute initialRoute;
+
+  TemplateRouteParser(List<String> pathTemplates,
+      {String? initialRoute = '/', this.guard})
+      : initialRoute =
+            ParsedRoute(initialRoute ?? '/', initialRoute ?? '/', {}, {}) {
+    for (var template in pathTemplates) {
+      _addRoute(template);
+    }
+  }
+
+  void _addRoute(String pathTemplate) {
+    _pathTemplates.add(pathTemplate);
+  }
+
+  @override
+  Future<ParsedRoute> parseRouteInformation(
+      RouteInformation routeInformation) async {
+    return await _parse(routeInformation);
+  }
+
+  Future<ParsedRoute> _parse(RouteInformation routeInformation) async {
+    final path = routeInformation.location!;
+    final queryParams = Uri.parse(path).queryParameters;
+    var parsedRoute = initialRoute;
+
+    for (var pathTemplate in _pathTemplates) {
+      final parameters = <String>[];
+      var pathRegExp = pathToRegExp(pathTemplate, parameters: parameters);
+      if (pathRegExp.hasMatch(path)) {
+        final match = pathRegExp.matchAsPrefix(path);
+        if (match == null) continue;
+        final params = extract(parameters, match);
+        parsedRoute = ParsedRoute(path, pathTemplate, params, queryParams);
+      }
+    }
+
+    // Redirect if a guard is present
+    var guard = this.guard;
+    if (guard != null) {
+      return guard.redirect(parsedRoute);
+    }
+
+    return parsedRoute;
+  }
+
+  @override
+  RouteInformation restoreRouteInformation(ParsedRoute configuration) {
+    return RouteInformation(location: configuration.path);
+  }
+}

navigation_and_routing/lib/src/routing/route_state.dart

@@ -0,0 +1,50 @@
+// Copyright 2021, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter/widgets.dart';
+
+import 'parsed_route.dart';
+import 'parser.dart';
+
+/// The current route state. To change the current route, call obtain the state using
+/// `RouteState.of(context)` and call `go()`:
+///
+/// ```
+/// RouteState.of(context).go('/book/2');
+/// ```
+class RouteState extends ChangeNotifier {
+  TemplateRouteParser parser;
+  ParsedRoute _route;
+
+  RouteState(this.parser)
+      : _route = parser.initialRoute;
+
+  ParsedRoute get route => _route;
+
+  set route(ParsedRoute route) {
+    _route = route;
+    notifyListeners();
+  }
+
+  Future<void> go(String route) async {
+    this.route =
+        await parser.parseRouteInformation(RouteInformation(location: route));
+  }
+}
+
+/// Provides the current [RouteState] to descendent widgets in the tree.
+class RouteStateScope extends InheritedNotifier<RouteState> {
+  const RouteStateScope({
+    required RouteState notifier,
+    required Widget child,
+    Key? key,
+  }) : super(key: key, notifier: notifier, child: child);
+
+  static RouteState? of(BuildContext context) {
+    return context
+        .dependOnInheritedWidgetOfExactType<RouteStateScope>()
+        ?.notifier;
+  }
+}

navigation_and_routing/lib/src/screens/author_details.dart

@@ -0,0 +1,49 @@
+// Copyright 2021, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+
+import '../data.dart';
+import '../widgets/book_list.dart';
+import 'book_details.dart';
+
+class AuthorDetailsScreen extends StatelessWidget {
+  final Author author;
+
+  const AuthorDetailsScreen({
+    Key? key,
+    required this.author,
+  }) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: Text(author.name),
+      ),
+      body: Center(
+        child: Column(
+          children: [
+            Expanded(
+              child: BookList(
+                books: author.books,
+                onTap: (book) {
+                  Navigator.of(context).push<dynamic>(
+                    MaterialPageRoute<dynamic>(
+                      builder: (context) {
+                        return BookDetailsScreen(
+                          book: book,
+                        );
+                      },
+                    ),
+                  );
+                },
+              ),
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+}

navigation_and_routing/lib/src/screens/authors.dart

@@ -0,0 +1,30 @@
+// Copyright 2021, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+
+import '../routing.dart';
+import '../widgets/author_list.dart';
+import '../widgets/library_scope.dart';
+
+class AuthorsScreen extends StatelessWidget {
+  final String title = "Authors";
+
+  const AuthorsScreen({Key? key}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: Text(title),
+      ),
+      body: AuthorList(
+        authors: LibraryScope.of(context).allAuthors,
+        onTap: (author) {
+          RouteStateScope.of(context)!.go('/author/${author.id}');
+        },
+      ),
+    );
+  }
+}

navigation_and_routing/lib/src/screens/book_details.dart

@@ -0,0 +1,75 @@
+// Copyright 2021, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+import 'package:url_launcher/link.dart';
+
+import '../data.dart';
+import 'author_details.dart';
+
+class BookDetailsScreen extends StatelessWidget {
+  final Book? book;
+
+  const BookDetailsScreen({
+    Key? key,
+    this.book,
+  }) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    if (book == null) {
+      return const Scaffold(
+        body: Center(
+          child: Text('No book with found.'),
+        ),
+      );
+    }
+    return Scaffold(
+      appBar: AppBar(
+        title: Text(book!.title),
+      ),
+      body: Center(
+        child: Column(
+          children: [
+            Text(
+              book!.title,
+              style: Theme
+                  .of(context)
+                  .textTheme
+                  .headline4,
+            ),
+            Text(
+              book!.author.name,
+              style: Theme
+                  .of(context)
+                  .textTheme
+                  .subtitle1,
+            ),
+            TextButton(
+              child: const Text('View author (Push)'),
+              onPressed: () {
+                Navigator.of(context).push<void>(
+                  MaterialPageRoute<void>(
+                    builder: (context) {
+                      return AuthorDetailsScreen(author: book!.author);
+                    },
+                  ),
+                );
+              },
+            ),
+            Link(
+              uri: Uri.parse('/author/${book!.author.id}'),
+              builder: (context, followLink) {
+                return TextButton(
+                  child: const Text('View author (Link)'),
+                  onPressed: followLink,
+                );
+              },
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+}

navigation_and_routing/lib/src/screens/books.dart

@@ -0,0 +1,130 @@
+// Copyright 2021, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+
+import '../data.dart';
+import '../routing.dart';
+import '../widgets/book_list.dart';
+import '../widgets/library_scope.dart';
+
+class BooksScreen extends StatefulWidget {
+  final ParsedRoute currentRoute;
+
+  const BooksScreen({
+    Key? key,
+    required this.currentRoute,
+  }) : super(key: key);
+
+  @override
+  _BooksScreenState createState() => _BooksScreenState();
+}
+
+class _BooksScreenState extends State<BooksScreen>
+    with SingleTickerProviderStateMixin {
+  late TabController _tabController;
+
+  @override
+  void initState() {
+    super.initState();
+    _tabController = TabController(length: 3, vsync: this)
+      ..addListener(_handleTabIndexChanged);
+  }
+
+  @override
+  void dispose() {
+    _tabController.removeListener(_handleTabIndexChanged);
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final library = LibraryScope.of(context);
+    return Scaffold(
+      appBar: AppBar(
+        title: const Text('Books'),
+        bottom: TabBar(
+          controller: _tabController,
+          tabs: const [
+            Tab(
+              text: 'Popular',
+              icon: Icon(Icons.people),
+            ),
+            Tab(
+              text: 'New',
+              icon: Icon(Icons.new_releases),
+            ),
+            Tab(
+              text: 'All',
+              icon: Icon(Icons.list),
+            ),
+          ],
+        ),
+      ),
+      body: TabBarView(
+        controller: _tabController,
+        children: [
+          BookList(
+            books: library.popularBooks,
+            onTap: _handleBookTapped,
+          ),
+          BookList(
+            books: library.newBooks,
+            onTap: _handleBookTapped,
+          ),
+          BookList(
+            books: library.allBooks,
+            onTap: _handleBookTapped,
+          ),
+        ],
+      ),
+    );
+  }
+
+  String get title {
+    switch (_tabController.index) {
+      case 1:
+        return 'New';
+      case 2:
+        return 'All';
+      case 0:
+      default:
+        return 'Popular';
+    }
+  }
+
+  RouteState get routeState => RouteStateScope.of(context)!;
+
+  void _handleBookTapped(Book book) {
+    routeState.go('/book/${book.id}');
+  }
+
+  void _handleTabIndexChanged() {
+    switch (_tabController.index) {
+      case 1:
+        routeState.go('/books/new');
+        break;
+      case 2:
+        routeState.go('/books/all');
+        break;
+      case 0:
+      default:
+        routeState.go('/books/popular');
+        break;
+    }
+  }
+
+  @override
+  void didUpdateWidget(BooksScreen oldWidget) {
+    var newPath = routeState.route.pathTemplate;
+    if (newPath.startsWith('/books/popular')) {
+      _tabController.index = 0;
+    } else if (newPath.startsWith('/books/new')) {
+      _tabController.index = 1;
+    } else if (newPath == '/books/all') {
+      _tabController.index = 2;
+    }
+    super.didUpdateWidget(oldWidget);
+  }
+}

navigation_and_routing/lib/src/screens/navigator.dart

@@ -0,0 +1,111 @@
+import 'package:collection/collection.dart';
+import 'package:flutter/material.dart';
+
+import '../auth.dart';
+import '../data.dart';
+import '../routing.dart';
+import '../screens/sign_in.dart';
+import '../widgets/fade_transition_page.dart';
+import '../widgets/library_scope.dart';
+import 'author_details.dart';
+import 'book_details.dart';
+import 'scaffold.dart';
+
+/// Builds the top-level navigator for the app. The pages to display are based
+/// on the [routeState] that was parsed by the TemplateRouteParser.
+class BookstoreNavigator extends StatefulWidget {
+  final GlobalKey<NavigatorState> navigatorKey;
+  final BookstoreAuth auth;
+
+  const BookstoreNavigator({
+    required this.auth,
+    required this.navigatorKey,
+    Key? key,
+  }) : super(key: key);
+
+  @override
+  _BookstoreNavigatorState createState() => _BookstoreNavigatorState();
+}
+
+class _BookstoreNavigatorState extends State<BookstoreNavigator> {
+  final scaffoldKey = const ValueKey<String>('App scaffold');
+  final bookDetailsKey = const ValueKey<String>('Book details screen');
+  final authorDetailsKey = const ValueKey<String>('Author details screen');
+
+  @override
+  Widget build(BuildContext context) {
+    final routeState = RouteStateScope.of(context)!;
+    final pathTemplate = routeState.route.pathTemplate;
+    final library = LibraryScope.of(context);
+
+    Book? book;
+    if (pathTemplate == '/book/:bookId') {
+      book = library.allBooks.firstWhereOrNull(
+          (b) => b.id.toString() == routeState.route.parameters['bookId']);
+    }
+
+    Author? author;
+    if (pathTemplate == '/author/:authorId') {
+      author = library.allAuthors.firstWhereOrNull(
+          (b) => b.id.toString() == routeState.route.parameters['authorId']);
+    }
+
+    return Navigator(
+      key: widget.navigatorKey,
+      onPopPage: (route, dynamic result) {
+        // When a page that is stacked on top of the scaffold is popped, display
+        // the /books or /authors tab in BookstoreScaffold.
+        if (route.settings is Page &&
+            (route.settings as Page).key == bookDetailsKey) {
+          routeState.go('/books/popular');
+        }
+
+        if (route.settings is Page &&
+            (route.settings as Page).key == authorDetailsKey) {
+          routeState.go('/authors');
+        }
+
+        return route.didPop(result);
+      },
+      pages: [
+        if (routeState.route.pathTemplate == '/signin')
+          // Display the sign in screen.
+          FadeTransitionPage<void>(
+            key: const ValueKey('Sign in'),
+            child: SignInScreen(
+              onSignIn: (credentials) async {
+                var signedIn = await widget.auth
+                    .signIn(credentials.username, credentials.password);
+                if (signedIn) {
+                  routeState.go('/books/popular');
+                }
+              },
+            ),
+          )
+        else ...[
+          // Display the app
+          FadeTransitionPage<void>(
+            key: scaffoldKey,
+            child: const BookstoreScaffold(),
+          ),
+          // Add an additional page to the stack if the user is viewing a book
+          // or an author
+          if (book != null)
+            MaterialPage<void>(
+              key: bookDetailsKey,
+              child: BookDetailsScreen(
+                book: book,
+              ),
+            )
+          else if (author != null)
+            MaterialPage<void>(
+              key: authorDetailsKey,
+              child: AuthorDetailsScreen(
+                author: author,
+              ),
+            ),
+        ],
+      ],
+    );
+  }
+}

navigation_and_routing/lib/src/screens/scaffold.dart

@@ -0,0 +1,54 @@
+// Copyright 2021, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:adaptive_navigation/adaptive_navigation.dart';
+import 'package:flutter/material.dart';
+
+import '../routing.dart';
+import 'scaffold_body.dart';
+
+class BookstoreScaffold extends StatelessWidget {
+  const BookstoreScaffold({
+    Key? key,
+  }) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    final routeState = RouteStateScope.of(context)!;
+    final selectedIndex = _getSelectedIndex(routeState.route.pathTemplate);
+
+    return Scaffold(
+      body: AdaptiveNavigationScaffold(
+        selectedIndex: selectedIndex,
+        body: const BookstoreScaffoldBody(),
+        onDestinationSelected: (idx) {
+          if (idx == 0) routeState.go('/books/popular');
+          if (idx == 1) routeState.go('/authors');
+          if (idx == 2) routeState.go('/settings');
+        },
+        destinations: const [
+          AdaptiveScaffoldDestination(
+            title: 'Books',
+            icon: Icons.book,
+          ),
+          AdaptiveScaffoldDestination(
+            title: 'Authors',
+            icon: Icons.person,
+          ),
+          AdaptiveScaffoldDestination(
+            title: 'Settings',
+            icon: Icons.settings,
+          ),
+        ],
+      ),
+    );
+  }
+
+  int _getSelectedIndex(String pathTemplate) {
+    if (pathTemplate.startsWith('/books')) return 0;
+    if (pathTemplate == '/authors') return 1;
+    if (pathTemplate == '/settings') return 2;
+    return 0;
+  }
+}

navigation_and_routing/lib/src/screens/scaffold_body.dart

@@ -0,0 +1,62 @@
+// Copyright 2021, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+
+import '../routing.dart';
+import '../screens/settings.dart';
+import '../widgets/fade_transition_page.dart';
+import 'authors.dart';
+import 'books.dart';
+
+/// Displays the contents of the body of [BookstoreScaffold]
+class BookstoreScaffoldBody extends StatelessWidget {
+  static GlobalKey<NavigatorState> navigatorKey = GlobalKey<NavigatorState>();
+
+  const BookstoreScaffoldBody({
+    Key? key,
+  }) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    var currentRoute = RouteStateScope.of(context)!.route;
+
+    // A nested Router isn't necessary because the back button behavior doesn't
+    // need to be customized.
+    return Navigator(
+      key: navigatorKey,
+      onPopPage: (route, dynamic result) => route.didPop(result),
+      pages: [
+        if (currentRoute.pathTemplate.startsWith('/authors'))
+          const FadeTransitionPage<void>(
+            key: ValueKey('authors'),
+            child: AuthorsScreen(),
+          )
+        else if (currentRoute.pathTemplate.startsWith('/settings'))
+          const FadeTransitionPage<void>(
+            key: ValueKey('settings'),
+            child: SettingsScreen(),
+          )
+        else if (currentRoute.pathTemplate.startsWith('/books') ||
+            currentRoute.pathTemplate == '/')
+          FadeTransitionPage<void>(
+            key: const ValueKey('books'),
+            child: BooksScreen(currentRoute: currentRoute),
+          )
+
+          // Avoid building a Navigator with an empty `pages` list when the
+          // RouteState is set to an unexpected path, such as /signin.
+          //
+          // Since RouteStateScope is an InheritedNotifier, any change to the
+          // route will result in a call to this build method, even though this
+          // widget isn't built when those routes are active.
+        else
+          FadeTransitionPage<void>(
+            key: const ValueKey('empty'),
+            child: Container(),
+          ),
+      ],
+    );
+  }
+}

navigation_and_routing/lib/src/screens/settings.dart

@@ -0,0 +1,103 @@
+// Copyright 2021, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+import 'package:url_launcher/link.dart';
+
+import '../auth/auth.dart';
+
+class SettingsScreen extends StatefulWidget {
+  const SettingsScreen({Key? key}) : super(key: key);
+
+  @override
+  _SettingsScreenState createState() => _SettingsScreenState();
+}
+
+class _SettingsScreenState extends State<SettingsScreen> {
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      body: SafeArea(
+        child: SingleChildScrollView(
+          child: Align(
+            alignment: Alignment.topCenter,
+            child: ConstrainedBox(
+              constraints: const BoxConstraints(maxWidth: 400),
+              child: const Card(
+                child: Padding(
+                  padding: EdgeInsets.symmetric(vertical: 18, horizontal: 12),
+                  child: SettingsContent(),
+                ),
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+  }
+}
+
+class SettingsContent extends StatelessWidget {
+  const SettingsContent({
+    Key? key,
+  }) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return Column(
+      children: [
+        ...[
+          Text(
+            'Settings',
+            style: Theme.of(context).textTheme.headline4,
+          ),
+          ElevatedButton(
+            onPressed: () {
+              BookstoreAuthScope.of(context)!.signOut();
+            },
+            child: const Text('Sign out'),
+          ),
+          Link(
+            uri: Uri.parse('/book/0'),
+            builder: (context, followLink) {
+              return TextButton(
+                child: const Text('Go directly to /book/0'),
+                onPressed: followLink,
+              );
+            },
+          ),
+          Link(
+            uri: Uri.parse('/author/0'),
+            builder: (context, followLink) {
+              return TextButton(
+                child: const Text('Go directly to /author/0'),
+                onPressed: followLink,
+              );
+            },
+          ),
+        ].map((w) => Padding(padding: const EdgeInsets.all(8), child: w)),
+        TextButton(
+          onPressed: () => showDialog<String>(
+            context: context,
+            builder: (context) => AlertDialog(
+              title: const Text('Alert!'),
+              content: const Text('The alert description goes here.'),
+              actions: <Widget>[
+                TextButton(
+                  onPressed: () => Navigator.pop(context, 'Cancel'),
+                  child: const Text('Cancel'),
+                ),
+                TextButton(
+                  onPressed: () => Navigator.pop(context, 'OK'),
+                  child: const Text('OK'),
+                ),
+              ],
+            ),
+          ),
+          child: const Text('Show Dialog'),
+        )
+      ],
+    );
+  }
+}

navigation_and_routing/lib/src/screens/sign_in.dart

@@ -0,0 +1,76 @@
+// Copyright 2021, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:flutter/cupertino.dart';
+import 'package:flutter/material.dart';
+
+class Credentials {
+  final String username;
+  final String password;
+  Credentials(this.username, this.password);
+}
+
+class SignInScreen extends StatefulWidget {
+  final ValueChanged<Credentials> onSignIn;
+
+  const SignInScreen({
+    required this.onSignIn,
+    Key? key,
+  }) : super(key: key);
+
+  @override
+  _SignInScreenState createState() => _SignInScreenState();
+}
+
+class _SignInScreenState extends State<SignInScreen> {
+  String username = '';
+  String password = '';
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      body: Center(
+        child: Card(
+          child: Container(
+            constraints: BoxConstraints.loose(const Size(600, 600)),
+            padding: const EdgeInsets.all(8),
+            child: Column(
+              mainAxisAlignment: MainAxisAlignment.center,
+              mainAxisSize: MainAxisSize.min,
+              children: [
+                Text('Sign in', style: Theme.of(context).textTheme.headline4),
+                TextField(
+                  decoration: const InputDecoration(labelText: 'Username'),
+                  onChanged: (v) {
+                    setState(() {
+                      username = v;
+                    });
+                  },
+                ),
+                TextField(
+                  decoration: const InputDecoration(labelText: 'Password'),
+                  obscureText: true,
+                  onChanged: (v) {
+                    setState(() {
+                      password = v;
+                    });
+                  },
+                ),
+                Padding(
+                  padding: const EdgeInsets.all(16),
+                  child: TextButton(
+                    onPressed: () async {
+                      widget.onSignIn(Credentials(username, password));
+                    },
+                    child: const Text('Sign in'),
+                  ),
+                ),
+              ],
+            ),
+          ),
+        ),
+      ),
+    );
+  }
+}

navigation_and_routing/lib/src/widgets/author_list.dart

@@ -0,0 +1,36 @@
+// Copyright 2021, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+
+import '../data.dart';
+
+class AuthorList extends StatelessWidget {
+  final List<Author> authors;
+  final ValueChanged<Author>? onTap;
+
+  const AuthorList({
+    required this.authors,
+    this.onTap,
+    Key? key,
+  }) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return ListView.builder(
+      itemCount: authors.length,
+      itemBuilder: (context, index) {
+        return ListTile(
+          title: Text(
+            authors[index].name,
+          ),
+          subtitle: Text(
+            '${authors[index].books.length} books',
+          ),
+          onTap: onTap != null ? () => onTap!(authors[index]) : null,
+        );
+      },
+    );
+  }
+}

navigation_and_routing/lib/src/widgets/book_list.dart

@@ -0,0 +1,36 @@
+// Copyright 2021, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+
+import '../data.dart';
+
+class BookList extends StatelessWidget {
+  final List<Book> books;
+  final ValueChanged<Book>? onTap;
+
+  const BookList({
+    required this.books,
+    this.onTap,
+    Key? key,
+  }) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return ListView.builder(
+      itemCount: books.length,
+      itemBuilder: (context, index) {
+        return ListTile(
+          title: Text(
+            books[index].title,
+          ),
+          subtitle: Text(
+            books[index].author.name,
+          ),
+          onTap: onTap != null ? () => onTap!(books[index]) : null,
+        );
+      },
+    );
+  }
+}

navigation_and_routing/lib/src/widgets/fade_transition_page.dart

@@ -0,0 +1,52 @@
+// Copyright 2021, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+
+class FadeTransitionPage<T> extends Page<T> {
+  final Widget child;
+
+  const FadeTransitionPage({LocalKey? key, required this.child})
+      : super(key: key);
+
+  @override
+  Route<T> createRoute(BuildContext context) {
+    return PageBasedFadeTransitionRoute<T>(this);
+  }
+}
+
+class PageBasedFadeTransitionRoute<T> extends PageRoute<T> {
+  PageBasedFadeTransitionRoute(Page page)
+      : super(
+          settings: page,
+        );
+
+  @override
+  Color? get barrierColor => null;
+
+  @override
+  String? get barrierLabel => null;
+
+  @override
+  Duration get transitionDuration => const Duration(milliseconds: 300);
+
+  @override
+  bool get maintainState => true;
+
+  @override
+  Widget buildPage(BuildContext context, Animation<double> animation,
+      Animation<double> secondaryAnimation) {
+    var curveTween = CurveTween(curve: Curves.easeIn);
+    return FadeTransition(
+      opacity: animation.drive(curveTween),
+      child: (settings as FadeTransitionPage).child,
+    );
+  }
+
+  @override
+  Widget buildTransitions(BuildContext context, Animation<double> animation,
+      Animation<double> secondaryAnimation, Widget child) {
+    return child;
+  }
+}

navigation_and_routing/lib/src/widgets/library_scope.dart

@@ -0,0 +1,25 @@
+// Copyright 2021, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:flutter/widgets.dart';
+
+import '../data.dart';
+
+class LibraryScope extends InheritedWidget {
+  final Library library;
+
+  const LibraryScope({
+    Key? key,
+    required this.library,
+    required Widget child,
+  }) : super(key: key, child: child);
+
+  @override
+  bool updateShouldNotify(LibraryScope oldWidget) =>
+      library != oldWidget.library;
+
+  static Library of(BuildContext context) {
+    return context.dependOnInheritedWidgetOfExactType<LibraryScope>()!.library;
+  }
+}