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

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']);
     }