9

lib/13/go/books/main.dart

@@ -0,0 +1,171 @@
+// Copyright 2013 The Flutter Authors. 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:flutter/material.dart';
+import 'package:go_router/go_router.dart';
+
+import 'src/auth.dart';
+import 'src/data/author.dart';
+import 'src/data/book.dart';
+import 'src/data/library.dart';
+import 'src/screens/author_details.dart';
+import 'src/screens/authors.dart';
+import 'src/screens/book_details.dart';
+import 'src/screens/books.dart';
+import 'src/screens/scaffold.dart';
+import 'src/screens/settings.dart';
+import 'src/screens/sign_in.dart';
+
+void main() => runApp(Bookstore());
+
+/// The book store view.
+class Bookstore extends StatelessWidget {
+  /// Creates a [Bookstore].
+  Bookstore({super.key});
+
+  final ValueKey<String> _scaffoldKey = const ValueKey<String>('App scaffold');
+
+  @override
+  Widget build(BuildContext context) => BookstoreAuthScope(
+        notifier: _auth,
+        child: MaterialApp.router(
+          routerConfig: _router,
+        ),
+      );
+
+  final BookstoreAuth _auth = BookstoreAuth();
+
+  late final GoRouter _router = GoRouter(
+    routes: <GoRoute>[
+      GoRoute(
+        path: '/',
+        redirect: (_, __) => '/books',
+      ),
+      GoRoute(
+        path: '/signin',
+        pageBuilder: (BuildContext context, GoRouterState state) =>
+            FadeTransitionPage(
+          key: state.pageKey,
+          child: SignInScreen(
+            onSignIn: (Credentials credentials) {
+              BookstoreAuthScope.of(context)
+                  .signIn(credentials.username, credentials.password);
+            },
+          ),
+        ),
+      ),
+      GoRoute(
+        path: '/books',
+        redirect: (_, __) => '/books/popular',
+      ),
+      GoRoute(
+        path: '/book/:bookId',
+        redirect: (BuildContext context, GoRouterState state) =>
+            '/books/all/${state.pathParameters['bookId']}',
+      ),
+      GoRoute(
+        path: '/books/:kind(new|all|popular)',
+        pageBuilder: (BuildContext context, GoRouterState state) =>
+            FadeTransitionPage(
+          key: _scaffoldKey,
+          child: BookstoreScaffold(
+            selectedTab: ScaffoldTab.books,
+            child: BooksScreen(state.pathParameters['kind']!),
+          ),
+        ),
+        routes: <GoRoute>[
+          GoRoute(
+            path: ':bookId',
+            builder: (BuildContext context, GoRouterState state) {
+              final String bookId = state.pathParameters['bookId']!;
+              final Book? selectedBook = libraryInstance.allBooks
+                  .firstWhereOrNull((Book b) => b.id.toString() == bookId);
+
+              return BookDetailsScreen(book: selectedBook);
+            },
+          ),
+        ],
+      ),
+      GoRoute(
+        path: '/author/:authorId',
+        redirect: (BuildContext context, GoRouterState state) =>
+            '/authors/${state.pathParameters['authorId']}',
+      ),
+      GoRoute(
+        path: '/authors',
+        pageBuilder: (BuildContext context, GoRouterState state) =>
+            FadeTransitionPage(
+          key: _scaffoldKey,
+          child: const BookstoreScaffold(
+            selectedTab: ScaffoldTab.authors,
+            child: AuthorsScreen(),
+          ),
+        ),
+        routes: <GoRoute>[
+          GoRoute(
+            path: ':authorId',
+            builder: (BuildContext context, GoRouterState state) {
+              final int authorId = int.parse(state.pathParameters['authorId']!);
+              final Author? selectedAuthor = libraryInstance.allAuthors
+                  .firstWhereOrNull((Author a) => a.id == authorId);
+
+              return AuthorDetailsScreen(author: selectedAuthor);
+            },
+          ),
+        ],
+      ),
+      GoRoute(
+        path: '/settings',
+        pageBuilder: (BuildContext context, GoRouterState state) =>
+            FadeTransitionPage(
+          key: _scaffoldKey,
+          child: const BookstoreScaffold(
+            selectedTab: ScaffoldTab.settings,
+            child: SettingsScreen(),
+          ),
+        ),
+      ),
+    ],
+    redirect: _guard,
+    refreshListenable: _auth,
+    debugLogDiagnostics: true,
+  );
+
+  String? _guard(BuildContext context, GoRouterState state) {
+    final bool signedIn = _auth.signedIn;
+    final bool signingIn = state.matchedLocation == '/signin';
+
+    // Go to /signin if the user is not signed in
+    if (!signedIn && !signingIn) {
+      return '/signin';
+    }
+    // Go to /books if the user is signed in and tries to go to /signin.
+    else if (signedIn && signingIn) {
+      return '/books';
+    }
+
+    // no redirect
+    return null;
+  }
+}
+
+/// A page that fades in an out.
+class FadeTransitionPage extends CustomTransitionPage<void> {
+  /// Creates a [FadeTransitionPage].
+  FadeTransitionPage({
+    required LocalKey super.key,
+    required super.child,
+  }) : super(
+            transitionsBuilder: (BuildContext context,
+                    Animation<double> animation,
+                    Animation<double> secondaryAnimation,
+                    Widget child) =>
+                FadeTransition(
+                  opacity: animation.drive(_curveTween),
+                  child: child,
+                ));
+
+  static final CurveTween _curveTween = CurveTween(curve: Curves.easeIn);
+}

lib/13/go/books/src/auth.dart

@@ -0,0 +1,46 @@
+// Copyright 2013 The Flutter Authors. 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';
+
+/// A mock authentication service.
+class BookstoreAuth extends ChangeNotifier {
+  bool _signedIn = false;
+
+  /// Whether user has signed in.
+  bool get signedIn => _signedIn;
+
+  /// Signs out the current user.
+  Future<void> signOut() async {
+    await Future<void>.delayed(const Duration(milliseconds: 200));
+    // Sign out.
+    _signedIn = false;
+    notifyListeners();
+  }
+
+  /// Signs in a user.
+  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;
+  }
+}
+
+/// An inherited notifier to host [BookstoreAuth] for the subtree.
+class BookstoreAuthScope extends InheritedNotifier<BookstoreAuth> {
+  /// Creates a [BookstoreAuthScope].
+  const BookstoreAuthScope({
+    required BookstoreAuth super.notifier,
+    required super.child,
+    super.key,
+  });
+
+  /// Gets the [BookstoreAuth] above the context.
+  static BookstoreAuth of(BuildContext context) => context
+      .dependOnInheritedWidgetOfExactType<BookstoreAuthScope>()!
+      .notifier!;
+}

lib/13/go/books/src/data.dart

@@ -0,0 +1,7 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+export 'data/author.dart';
+export 'data/book.dart';
+export 'data/library.dart';

lib/13/go/books/src/data/author.dart

@@ -0,0 +1,23 @@
+// Copyright 2013 The Flutter Authors. 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';
+
+/// Author data class.
+class Author {
+  /// Creates an author data object.
+  Author({
+    required this.id,
+    required this.name,
+  });
+
+  /// The id of the author.
+  final int id;
+
+  /// The name of the author.
+  final String name;
+
+  /// The books of the author.
+  final List<Book> books = <Book>[];
+}

lib/13/go/books/src/data/book.dart

@@ -0,0 +1,32 @@
+// Copyright 2013 The Flutter Authors. 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';
+
+/// Book data class.
+class Book {
+  /// Creates a book data object.
+  Book({
+    required this.id,
+    required this.title,
+    required this.isPopular,
+    required this.isNew,
+    required this.author,
+  });
+
+  /// The id of the book.
+  final int id;
+
+  /// The title of the book.
+  final String title;
+
+  /// The author of the book.
+  final Author author;
+
+  /// Whether the book is popular.
+  final bool isPopular;
+
+  /// Whether the book is new.
+  final bool isNew;
+}

lib/13/go/books/src/data/library.dart

@@ -0,0 +1,76 @@
+// Copyright 2013 The Flutter Authors. 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';
+import 'book.dart';
+
+/// Library data mock.
+final Library libraryInstance = Library()
+  ..addBook(
+      title: 'Left Hand of Darkness',
+      authorName: 'Ursula K. Le Guin',
+      isPopular: true,
+      isNew: true)
+  ..addBook(
+      title: 'Too Like the Lightning',
+      authorName: 'Ada Palmer',
+      isPopular: false,
+      isNew: true)
+  ..addBook(
+      title: 'Kindred',
+      authorName: 'Octavia E. Butler',
+      isPopular: true,
+      isNew: false)
+  ..addBook(
+      title: 'The Lathe of Heaven',
+      authorName: 'Ursula K. Le Guin',
+      isPopular: false,
+      isNew: false);
+
+/// A library that contains books and authors.
+class Library {
+  /// The books in the library.
+  final List<Book> allBooks = <Book>[];
+
+  /// The authors in the library.
+  final List<Author> allAuthors = <Author>[];
+
+  /// Adds a book into the library.
+  void addBook({
+    required String title,
+    required String authorName,
+    required bool isPopular,
+    required bool isNew,
+  }) {
+    final Author author = allAuthors.firstWhere(
+      (Author author) => author.name == authorName,
+      orElse: () {
+        final Author value = Author(id: allAuthors.length, name: authorName);
+        allAuthors.add(value);
+        return value;
+      },
+    );
+
+    final Book book = Book(
+      id: allBooks.length,
+      title: title,
+      isPopular: isPopular,
+      isNew: isNew,
+      author: author,
+    );
+
+    author.books.add(book);
+    allBooks.add(book);
+  }
+
+  /// The list of popular books in the library.
+  List<Book> get popularBooks => <Book>[
+        ...allBooks.where((Book book) => book.isPopular),
+      ];
+
+  /// The list of new books in the library.
+  List<Book> get newBooks => <Book>[
+        ...allBooks.where((Book book) => book.isNew),
+      ];
+}

lib/13/go/books/src/screens/author_details.dart

@@ -0,0 +1,49 @@
+// Copyright 2013 The Flutter Authors. 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:go_router/go_router.dart';
+
+import '../data.dart';
+import '../widgets/book_list.dart';
+
+/// The author detail screen.
+class AuthorDetailsScreen extends StatelessWidget {
+  /// Creates an author detail screen.
+  const AuthorDetailsScreen({
+    required this.author,
+    super.key,
+  });
+
+  /// The author to be displayed.
+  final Author? author;
+
+  @override
+  Widget build(BuildContext context) {
+    if (author == null) {
+      return const Scaffold(
+        body: Center(
+          child: Text('No author found.'),
+        ),
+      );
+    }
+    return Scaffold(
+      appBar: AppBar(
+        title: Text(author!.name),
+      ),
+      body: Center(
+        child: Column(
+          children: <Widget>[
+            Expanded(
+              child: BookList(
+                books: author!.books,
+                onTap: (Book book) => context.go('/book/${book.id}'),
+              ),
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+}

lib/13/go/books/src/screens/authors.dart

@@ -0,0 +1,31 @@
+// Copyright 2013 The Flutter Authors. 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:go_router/go_router.dart';
+
+import '../data.dart';
+import '../widgets/author_list.dart';
+
+/// A screen that displays a list of authors.
+class AuthorsScreen extends StatelessWidget {
+  /// Creates an [AuthorsScreen].
+  const AuthorsScreen({super.key});
+
+  /// The title of the screen.
+  static const String title = 'Authors';
+
+  @override
+  Widget build(BuildContext context) => Scaffold(
+        appBar: AppBar(
+          title: const Text(title),
+        ),
+        body: AuthorList(
+          authors: libraryInstance.allAuthors,
+          onTap: (Author author) {
+            context.go('/author/${author.id}');
+          },
+        ),
+      );
+}

lib/13/go/books/src/screens/book_details.dart

@@ -0,0 +1,77 @@
+// Copyright 2013 The Flutter Authors. 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:go_router/go_router.dart';
+import 'package:url_launcher/link.dart';
+
+import '../data.dart';
+import 'author_details.dart';
+
+/// A screen to display book details.
+class BookDetailsScreen extends StatelessWidget {
+  /// Creates a [BookDetailsScreen].
+  const BookDetailsScreen({
+    super.key,
+    this.book,
+  });
+
+  /// The book to be displayed.
+  final Book? book;
+
+  @override
+  Widget build(BuildContext context) {
+    if (book == null) {
+      return const Scaffold(
+        body: Center(
+          child: Text('No book found.'),
+        ),
+      );
+    }
+    return Scaffold(
+      appBar: AppBar(
+        title: Text(book!.title),
+      ),
+      body: Center(
+        child: Column(
+          children: <Widget>[
+            Text(
+              book!.title,
+              style: Theme.of(context).textTheme.headlineMedium,
+            ),
+            Text(
+              book!.author.name,
+              style: Theme.of(context).textTheme.titleMedium,
+            ),
+            TextButton(
+              onPressed: () {
+                Navigator.of(context).push<void>(
+                  MaterialPageRoute<void>(
+                    builder: (BuildContext context) =>
+                        AuthorDetailsScreen(author: book!.author),
+                  ),
+                );
+              },
+              child: const Text('View author (navigator.push)'),
+            ),
+            Link(
+              uri: Uri.parse('/author/${book!.author.id}'),
+              builder: (BuildContext context, FollowLink? followLink) =>
+                  TextButton(
+                onPressed: followLink,
+                child: const Text('View author (Link)'),
+              ),
+            ),
+            TextButton(
+              onPressed: () {
+                context.push('/author/${book!.author.id}');
+              },
+              child: const Text('View author (GoRouter.push)'),
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+}

lib/13/go/books/src/screens/books.dart

@@ -0,0 +1,118 @@
+// Copyright 2013 The Flutter Authors. 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:go_router/go_router.dart';
+
+import '../data.dart';
+import '../widgets/book_list.dart';
+
+/// A screen that displays a list of books.
+class BooksScreen extends StatefulWidget {
+  /// Creates a [BooksScreen].
+  const BooksScreen(this.kind, {super.key});
+
+  /// Which tab to display.
+  final String kind;
+
+  @override
+  State<BooksScreen> createState() => _BooksScreenState();
+}
+
+class _BooksScreenState extends State<BooksScreen>
+    with SingleTickerProviderStateMixin {
+  late TabController _tabController;
+
+  @override
+  void initState() {
+    super.initState();
+    _tabController = TabController(length: 3, vsync: this);
+  }
+
+  @override
+  void didUpdateWidget(BooksScreen oldWidget) {
+    super.didUpdateWidget(oldWidget);
+
+    switch (widget.kind) {
+      case 'popular':
+        _tabController.index = 0;
+        break;
+
+      case 'new':
+        _tabController.index = 1;
+        break;
+
+      case 'all':
+        _tabController.index = 2;
+        break;
+    }
+  }
+
+  @override
+  void dispose() {
+    _tabController.dispose();
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) => Scaffold(
+        appBar: AppBar(
+          title: const Text('Books'),
+          bottom: TabBar(
+            controller: _tabController,
+            onTap: _handleTabTapped,
+            tabs: const <Tab>[
+              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: <Widget>[
+            BookList(
+              books: libraryInstance.popularBooks,
+              onTap: _handleBookTapped,
+            ),
+            BookList(
+              books: libraryInstance.newBooks,
+              onTap: _handleBookTapped,
+            ),
+            BookList(
+              books: libraryInstance.allBooks,
+              onTap: _handleBookTapped,
+            ),
+          ],
+        ),
+      );
+
+  void _handleBookTapped(Book book) {
+    context.go('/book/${book.id}');
+  }
+
+  void _handleTabTapped(int index) {
+    switch (index) {
+      case 1:
+        context.go('/books/new');
+        break;
+      case 2:
+        context.go('/books/all');
+        break;
+      case 0:
+      default:
+        context.go('/books/popular');
+        break;
+    }
+  }
+}

lib/13/go/books/src/screens/scaffold.dart

@@ -0,0 +1,71 @@
+// Copyright 2013 The Flutter Authors. 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 'package:go_router/go_router.dart';
+
+/// The enum for scaffold tab.
+enum ScaffoldTab {
+  /// The books tab.
+  books,
+
+  /// The authors tab.
+  authors,
+
+  /// The settings tab.
+  settings
+}
+
+/// The scaffold for the book store.
+class BookstoreScaffold extends StatelessWidget {
+  /// Creates a [BookstoreScaffold].
+  const BookstoreScaffold({
+    required this.selectedTab,
+    required this.child,
+    super.key,
+  });
+
+  /// Which tab of the scaffold to display.
+  final ScaffoldTab selectedTab;
+
+  /// The scaffold body.
+  final Widget child;
+
+  @override
+  Widget build(BuildContext context) => Scaffold(
+        body: AdaptiveNavigationScaffold(
+          selectedIndex: selectedTab.index,
+          body: child,
+          onDestinationSelected: (int idx) {
+            switch (ScaffoldTab.values[idx]) {
+              case ScaffoldTab.books:
+                context.go('/books');
+                break;
+              case ScaffoldTab.authors:
+                context.go('/authors');
+                break;
+              case ScaffoldTab.settings:
+                context.go('/settings');
+                break;
+            }
+          },
+          destinations: const <AdaptiveScaffoldDestination>[
+            AdaptiveScaffoldDestination(
+              title: 'Books',
+              icon: Icons.book,
+            ),
+            AdaptiveScaffoldDestination(
+              title: 'Authors',
+              icon: Icons.person,
+            ),
+            AdaptiveScaffoldDestination(
+              title: 'Settings',
+              icon: Icons.settings,
+            ),
+          ],
+        ),
+      );
+}

lib/13/go/books/src/screens/settings.dart

@@ -0,0 +1,101 @@
+// Copyright 2013 The Flutter Authors. 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:go_router/go_router.dart';
+import 'package:url_launcher/link.dart';
+
+import '../auth.dart';
+
+/// The settings screen.
+class SettingsScreen extends StatefulWidget {
+  /// Creates a [SettingsScreen].
+  const SettingsScreen({super.key});
+
+  @override
+  State<SettingsScreen> createState() => _SettingsScreenState();
+}
+
+class _SettingsScreenState extends State<SettingsScreen> {
+  @override
+  Widget build(BuildContext context) => 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(),
+                  ),
+                ),
+              ),
+            ),
+          ),
+        ),
+      );
+}
+
+/// The content of a [SettingsScreen].
+class SettingsContent extends StatelessWidget {
+  /// Creates a [SettingsContent].
+  const SettingsContent({
+    super.key,
+  });
+
+  @override
+  Widget build(BuildContext context) => Column(
+        children: <Widget>[
+          ...<Widget>[
+            Text(
+              'Settings',
+              style: Theme.of(context).textTheme.headlineMedium,
+            ),
+            ElevatedButton(
+              onPressed: () {
+                BookstoreAuthScope.of(context).signOut();
+              },
+              child: const Text('Sign out'),
+            ),
+            Link(
+              uri: Uri.parse('/book/0'),
+              builder: (BuildContext context, FollowLink? followLink) =>
+                  TextButton(
+                onPressed: followLink,
+                child: const Text('Go directly to /book/0 (Link)'),
+              ),
+            ),
+            TextButton(
+              onPressed: () {
+                context.go('/book/0');
+              },
+              child: const Text('Go directly to /book/0 (GoRouter)'),
+            ),
+          ].map<Widget>((Widget w) =>
+              Padding(padding: const EdgeInsets.all(8), child: w)),
+          TextButton(
+            onPressed: () => showDialog<String>(
+              context: context,
+              builder: (BuildContext 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'),
+          )
+        ],
+      );
+}

lib/13/go/books/src/screens/sign_in.dart

@@ -0,0 +1,77 @@
+// Copyright 2013 The Flutter Authors. 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';
+
+/// Credential data class.
+class Credentials {
+  /// Creates a credential data object.
+  Credentials(this.username, this.password);
+
+  /// The username of the credentials.
+  final String username;
+
+  /// The password of the credentials.
+  final String password;
+}
+
+/// The sign-in screen.
+class SignInScreen extends StatefulWidget {
+  /// Creates a sign-in screen.
+  const SignInScreen({
+    required this.onSignIn,
+    super.key,
+  });
+
+  /// Called when users sign in with [Credentials].
+  final ValueChanged<Credentials> onSignIn;
+
+  @override
+  State<SignInScreen> createState() => _SignInScreenState();
+}
+
+class _SignInScreenState extends State<SignInScreen> {
+  final TextEditingController _usernameController = TextEditingController();
+  final TextEditingController _passwordController = TextEditingController();
+
+  @override
+  Widget build(BuildContext context) => 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: <Widget>[
+                  Text('Sign in',
+                      style: Theme.of(context).textTheme.headlineMedium),
+                  TextField(
+                    decoration: const InputDecoration(labelText: 'Username'),
+                    controller: _usernameController,
+                  ),
+                  TextField(
+                    decoration: const InputDecoration(labelText: 'Password'),
+                    obscureText: true,
+                    controller: _passwordController,
+                  ),
+                  Padding(
+                    padding: const EdgeInsets.all(16),
+                    child: TextButton(
+                      onPressed: () async {
+                        widget.onSignIn(Credentials(
+                            _usernameController.value.text,
+                            _passwordController.value.text));
+                      },
+                      child: const Text('Sign in'),
+                    ),
+                  ),
+                ],
+              ),
+            ),
+          ),
+        ),
+      );
+}

lib/13/go/books/src/widgets/author_list.dart

@@ -0,0 +1,37 @@
+// Copyright 2013 The Flutter Authors. 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';
+
+/// The author list view.
+class AuthorList extends StatelessWidget {
+  /// Creates an [AuthorList].
+  const AuthorList({
+    required this.authors,
+    this.onTap,
+    super.key,
+  });
+
+  /// The list of authors to be shown.
+  final List<Author> authors;
+
+  /// Called when the user taps an author.
+  final ValueChanged<Author>? onTap;
+
+  @override
+  Widget build(BuildContext context) => ListView.builder(
+        itemCount: authors.length,
+        itemBuilder: (BuildContext context, int index) => ListTile(
+          title: Text(
+            authors[index].name,
+          ),
+          subtitle: Text(
+            '${authors[index].books.length} books',
+          ),
+          onTap: onTap != null ? () => onTap!(authors[index]) : null,
+        ),
+      );
+}

lib/13/go/books/src/widgets/book_list.dart

@@ -0,0 +1,37 @@
+// Copyright 2013 The Flutter Authors. 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';
+
+/// The book list view.
+class BookList extends StatelessWidget {
+  /// Creates an [BookList].
+  const BookList({
+    required this.books,
+    this.onTap,
+    super.key,
+  });
+
+  /// The list of books to be displayed.
+  final List<Book> books;
+
+  /// Called when the user taps a book.
+  final ValueChanged<Book>? onTap;
+
+  @override
+  Widget build(BuildContext context) => ListView.builder(
+        itemCount: books.length,
+        itemBuilder: (BuildContext context, int index) => ListTile(
+          title: Text(
+            books[index].title,
+          ),
+          subtitle: Text(
+            books[index].author.name,
+          ),
+          onTap: onTap != null ? () => onTap!(books[index]) : null,
+        ),
+      );
+}