State Restoration support for Veggie Seasons app (#433)

experimental/veggieseasons/lib/main.dart

@@ -0,0 +1,89 @@
+// Copyright 2018 The Flutter team. 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/services.dart' show DeviceOrientation, SystemChrome;
+import 'package:provider/provider.dart';
+import 'package:veggieseasons/data/app_state.dart';
+import 'package:veggieseasons/data/preferences.dart';
+import 'package:veggieseasons/screens/home.dart';
+
+void main() {
+  WidgetsFlutterBinding.ensureInitialized();
+  SystemChrome.setPreferredOrientations([
+    DeviceOrientation.portraitUp,
+    DeviceOrientation.portraitDown,
+  ]);
+
+  runApp(
+    RootRestorationScope(
+      restorationId: 'root',
+      child: VeggieApp(),
+    ),
+  );
+}
+
+class VeggieApp extends StatefulWidget {
+  @override
+  State<StatefulWidget> createState() => _VeggieAppState();
+}
+
+class _VeggieAppState extends State<VeggieApp> with RestorationMixin {
+  final _RestorableAppState _appState = _RestorableAppState();
+
+  @override
+  String get restorationId => 'wrapper';
+
+  @override
+  void restoreState(RestorationBucket oldBucket, bool initialRestore) {
+    registerForRestoration(_appState, 'state');
+  }
+
+  @override
+  void dispose() {
+    _appState.dispose();
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return MultiProvider(
+      providers: [
+        ChangeNotifierProvider.value(
+          value: _appState.value,
+        ),
+        ChangeNotifierProvider(
+          create: (_) => Preferences()..load(),
+        ),
+      ],
+      child: CupertinoApp(
+        debugShowCheckedModeBanner: false,
+        home: HomeScreen(restorationId: 'home'),
+        restorationScopeId: 'app',
+      ),
+    );
+  }
+}
+
+class _RestorableAppState extends RestorableListenable<AppState> {
+  @override
+  AppState createDefaultValue() {
+    return AppState();
+  }
+
+  @override
+  AppState fromPrimitives(Object data) {
+    final appState = AppState();
+    final favorites = (data as List<dynamic>).cast<int>();
+    for (var id in favorites) {
+      appState.setFavorite(id, true);
+    }
+    return appState;
+  }
+
+  @override
+  Object toPrimitives() {
+    return value.favoriteVeggies.map((veggie) => veggie.id).toList();
+  }
+}