Move library to a top-level variable, since it never changes (#887)

navigation_and_routing/lib/src/app.dart

@@ -5,10 +5,8 @@
 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);
@@ -24,28 +22,6 @@ class _BookstoreState extends State<Bookstore> {
   late final SimpleRouterDelegate _routerDelegate;
   late final TemplateRouteParser _routeParser;
 
-  final library = 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);
-
   @override
   void initState() {
     /// Configure the parser with all of the app's allowed path templates.
@@ -85,12 +61,9 @@ class _BookstoreState extends State<Bookstore> {
         notifier: _routeState,
         child: BookstoreAuthScope(
           notifier: _auth,
-          child: LibraryScope(
-            library: library,
-            child: MaterialApp.router(
-              routerDelegate: _routerDelegate,
-              routeInformationParser: _routeParser,
-            ),
+          child: MaterialApp.router(
+            routerDelegate: _routerDelegate,
+            routeInformationParser: _routeParser,
           ),
         ),
       );

navigation_and_routing/lib/src/data/author.dart

@@ -7,7 +7,7 @@ import 'book.dart';
 class Author {
   final int id;
   final String name;
-  final List<Book> books;
+  final List<Book> books = <Book>[];
 
-  Author(this.id, this.name, this.books);
+  Author(this.id, this.name);
 }

navigation_and_routing/lib/src/data/book.dart

@@ -7,9 +7,9 @@ import 'author.dart';
 class Book {
   final int id;
   final String title;
-  late final Author author;
+  final Author author;
   final bool isPopular;
   final bool isNew;
 
-  Book(this.id, this.title, this.isPopular, this.isNew);
+  Book(this.id, this.title, this.isPopular, this.isNew, this.author);
 }

navigation_and_routing/lib/src/data/library.dart

@@ -2,11 +2,31 @@
 // 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';
 
+final 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);
+
 class Library {
   final List<Book> allBooks = [];
   final List<Author> allAuthors = [];
@@ -17,18 +37,17 @@ class Library {
     required bool isPopular,
     required bool isNew,
   }) {
-    var author =
-        allAuthors.firstWhereOrNull((author) => author.name == authorName);
-    var book = Book(allBooks.length, title, isPopular, isNew);
+    var author = allAuthors.firstWhere(
+      (author) => author.name == authorName,
+      orElse: () {
+        final value = Author(allAuthors.length, authorName);
+        allAuthors.add(value);
+        return value;
+      },
+    );
+    var book = Book(allBooks.length, title, isPopular, isNew, author);
 
-    if (author == null) {
-      author = Author(allAuthors.length, authorName, [book]);
-      allAuthors.add(author);
-    } else {
-      author.books.add(book);
-    }
-
-    book.author = author;
+    author.books.add(book);
     allBooks.add(book);
   }
 

navigation_and_routing/lib/src/screens/authors.dart

@@ -4,9 +4,9 @@
 
 import 'package:flutter/material.dart';
 
+import '../data/library.dart';
 import '../routing.dart';
 import '../widgets/author_list.dart';
-import '../widgets/library_scope.dart';
 
 class AuthorsScreen extends StatelessWidget {
   final String title = 'Authors';
@@ -19,7 +19,7 @@ class AuthorsScreen extends StatelessWidget {
           title: Text(title),
         ),
         body: AuthorList(
-          authors: LibraryScope.of(context).allAuthors,
+          authors: libraryInstance.allAuthors,
           onTap: (author) {
             RouteStateScope.of(context).go('/author/${author.id}');
           },

navigation_and_routing/lib/src/screens/books.dart

@@ -7,7 +7,6 @@ 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 {
   const BooksScreen({
@@ -50,48 +49,45 @@ class _BooksScreenState extends State<BooksScreen>
   }
 
   @override
-  Widget build(BuildContext context) {
-    final library = LibraryScope.of(context);
-    return Scaffold(
-      appBar: AppBar(
-        title: const Text('Books'),
-        bottom: TabBar(
+  Widget build(BuildContext context) => 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,
-          tabs: const [
-            Tab(
-              text: 'Popular',
-              icon: Icon(Icons.people),
+          children: [
+            BookList(
+              books: libraryInstance.popularBooks,
+              onTap: _handleBookTapped,
             ),
-            Tab(
-              text: 'New',
-              icon: Icon(Icons.new_releases),
+            BookList(
+              books: libraryInstance.newBooks,
+              onTap: _handleBookTapped,
             ),
-            Tab(
-              text: 'All',
-              icon: Icon(Icons.list),
+            BookList(
+              books: libraryInstance.allBooks,
+              onTap: _handleBookTapped,
             ),
           ],
         ),
-      ),
-      body: TabBarView(
-        controller: _tabController,
-        children: [
-          BookList(
-            books: library.popularBooks,
-            onTap: _handleBookTapped,
-          ),
-          BookList(
-            books: library.newBooks,
-            onTap: _handleBookTapped,
-          ),
-          BookList(
-            books: library.allBooks,
-            onTap: _handleBookTapped,
-          ),
-        ],
-      ),
-    );
-  }
+      );
 
   RouteState get _routeState => RouteStateScope.of(context);
 

navigation_and_routing/lib/src/screens/navigator.dart

@@ -7,10 +7,10 @@ import 'package:flutter/material.dart';
 
 import '../auth.dart';
 import '../data.dart';
+import '../data/library.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';
@@ -40,17 +40,16 @@ class _BookstoreNavigatorState extends State<BookstoreNavigator> {
     final routeState = RouteStateScope.of(context);
     final authState = BookstoreAuthScope.of(context);
     final pathTemplate = routeState.route.pathTemplate;
-    final library = LibraryScope.of(context);
 
     Book? selectedBook;
     if (pathTemplate == '/book/:bookId') {
-      selectedBook = library.allBooks.firstWhereOrNull(
+      selectedBook = libraryInstance.allBooks.firstWhereOrNull(
           (b) => b.id.toString() == routeState.route.parameters['bookId']);
     }
 
     Author? selectedAuthor;
     if (pathTemplate == '/author/:authorId') {
-      selectedAuthor = library.allAuthors.firstWhereOrNull(
+      selectedAuthor = libraryInstance.allAuthors.firstWhereOrNull(
           (b) => b.id.toString() == routeState.route.parameters['authorId']);
     }
 

navigation_and_routing/lib/src/widgets/library_scope.dart

@@ -1,24 +0,0 @@
-// 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) =>
-      context.dependOnInheritedWidgetOfExactType<LibraryScope>()!.library;
-}