State Restoration support for Veggie Seasons app (#433)

experimental/veggieseasons/README.md

@@ -0,0 +1,42 @@
+# Veggie Seasons
+
+An iOS app that shows which fruits and vegetables are currently in season. It
+showcases Flutter's Cupertino package.
+
+[Available now in the App Store!](https://itunes.apple.com/is/app/veggie-seasons/id1450855435)
+
+**NOTE:** While Flutter supports many platforms, this application is designed
+specifically for iOS. It's not intended to be run on Android, web, or desktop.
+
+## Goals
+
+* Show how to build an interface that iOS users will feel right at home
+  with.
+* Show how Flutter's Cupertino widgets work together.
+
+## The important bits
+
+### `/screens/*`
+
+These are the screens presented in the app, roughly analogous to
+UIViewControllers. `HomeScreen` is the root, and the others are shown
+as the user navigates.
+
+### `/widgets/search_bar.dart`
+
+An example of how to construct an Cupertino-style search bar. The
+Flutter team [is working on an official widget](https://github.com/flutter/flutter/issues/9784)
+for this. Once that effort is complete, developers will not need to roll
+their own search bars, so to speak.
+
+## Questions/issues
+
+If you have a general question about any of the techniques you see in
+the sample, the best places to go are:
+
+* [The FlutterDev Google Group](https://groups.google.com/forum/#!forum/flutter-dev)
+* [The Flutter Gitter channel](https://gitter.im/flutter/flutter)
+* [StackOverflow](https://stackoverflow.com/questions/tagged/flutter)
+
+If you run into an issue with the sample itself, please file an issue
+in the [main Flutter repo](https://github.com/flutter/flutter/issues).

veggieseasons/lib/data/app_state.dart → experimental/veggieseasons/lib/data/app_state.dart

@@ -38,7 +38,14 @@ class AppState extends ChangeNotifier {
     notifyListeners();
   }
 
+  /// Used in tests to set the season independent of the current date.
+  static Season debugCurrentSeason;
+
   static Season _getSeasonForDate(DateTime date) {
+    if (debugCurrentSeason != null) {
+      return debugCurrentSeason;
+    }
+
     // Technically the start and end dates of seasons can vary by a day or so,
     // but this is close enough for produce.
     switch (date.month) {

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();
+  }
+}

veggieseasons/lib/screens/details.dart → experimental/veggieseasons/lib/screens/details.dart

@@ -238,15 +238,42 @@ class InfoView extends StatelessWidget {
 
 class DetailsScreen extends StatefulWidget {
   final int id;
+  final String restorationId;
 
-  DetailsScreen(this.id);
+  DetailsScreen({this.id, this.restorationId});
+
+  static String show(NavigatorState navigator, int veggieId) {
+    return navigator.restorablePush<void>(_routeBuilder, arguments: veggieId);
+  }
+
+  static Route<void> _routeBuilder(BuildContext context, Object arguments) {
+    final veggieId = arguments as int;
+    return CupertinoPageRoute(
+      builder: (context) => DetailsScreen(id: veggieId, restorationId: 'details'),
+      fullscreenDialog: true,
+    );
+  }
 
   @override
   _DetailsScreenState createState() => _DetailsScreenState();
 }
 
-class _DetailsScreenState extends State<DetailsScreen> {
-  int _selectedViewIndex = 0;
+class _DetailsScreenState extends State<DetailsScreen> with RestorationMixin {
+  final RestorableInt _selectedViewIndex = RestorableInt(0);
+
+  @override
+  String get restorationId => widget.restorationId;
+
+  @override
+  void restoreState(RestorationBucket oldBucket, bool initialRestore) {
+    registerForRestoration(_selectedViewIndex, 'tab');
+  }
+
+  @override
+  void dispose() {
+    _selectedViewIndex.dispose();
+    super.dispose();
+  }
 
   Widget _buildHeader(BuildContext context, AppState model) {
     final veggie = model.getVeggie(widget.id);
@@ -282,33 +309,37 @@ class _DetailsScreenState extends State<DetailsScreen> {
   Widget build(BuildContext context) {
     final appState = Provider.of<AppState>(context);
 
-    return CupertinoPageScaffold(
-      child: Column(
-        crossAxisAlignment: CrossAxisAlignment.stretch,
-        mainAxisSize: MainAxisSize.min,
-        children: [
-          Expanded(
-            child: ListView(
-              children: [
-                _buildHeader(context, appState),
-                SizedBox(height: 20),
-                CupertinoSegmentedControl<int>(
-                  children: {
-                    0: Text('Facts & Info'),
-                    1: Text('Trivia'),
-                  },
-                  groupValue: _selectedViewIndex,
-                  onValueChanged: (value) {
-                    setState(() => _selectedViewIndex = value);
-                  },
-                ),
-                _selectedViewIndex == 0
-                    ? InfoView(widget.id)
-                    : TriviaView(widget.id),
-              ],
+    return UnmanagedRestorationScope(
+      bucket: bucket,
+      child: CupertinoPageScaffold(
+        child: Column(
+          crossAxisAlignment: CrossAxisAlignment.stretch,
+          mainAxisSize: MainAxisSize.min,
+          children: [
+            Expanded(
+              child: ListView(
+                restorationId: 'list',
+                children: [
+                  _buildHeader(context, appState),
+                  SizedBox(height: 20),
+                  CupertinoSegmentedControl<int>(
+                    children: {
+                      0: Text('Facts & Info'),
+                      1: Text('Trivia'),
+                    },
+                    groupValue: _selectedViewIndex.value,
+                    onValueChanged: (value) {
+                      setState(() => _selectedViewIndex.value = value);
+                    },
+                  ),
+                  _selectedViewIndex.value == 0
+                      ? InfoView(widget.id)
+                      : TriviaView(id: widget.id, restorationId: 'trivia'),
+                ],
+              ),
             ),
-          ),
-        ],
+          ],
+        ),
       ),
     );
   }

veggieseasons/lib/screens/favorites.dart → experimental/veggieseasons/lib/screens/favorites.dart

@@ -11,9 +11,14 @@ import 'package:veggieseasons/styles.dart';
 import 'package:veggieseasons/widgets/veggie_headline.dart';
 
 class FavoritesScreen extends StatelessWidget {
+  FavoritesScreen({this.restorationId, Key key}) : super(key: key);
+
+  final String restorationId;
+
   @override
   Widget build(BuildContext context) {
     return CupertinoTabView(
+      restorationScopeId: restorationId,
       builder: (context) {
         final model = Provider.of<AppState>(context);
 
@@ -32,6 +37,7 @@ class FavoritesScreen extends StatelessWidget {
                     ),
                   )
                 : ListView(
+                    restorationId: 'list',
                     children: [
                       SizedBox(height: 24),
                       for (Veggie veggie in model.favoriteVeggies)

experimental/veggieseasons/lib/screens/home.dart

@@ -0,0 +1,55 @@
+// 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/widgets.dart';
+import 'package:veggieseasons/screens/favorites.dart';
+import 'package:veggieseasons/screens/list.dart';
+import 'package:veggieseasons/screens/search.dart';
+import 'package:veggieseasons/screens/settings.dart';
+
+class HomeScreen extends StatelessWidget {
+  HomeScreen({Key key, this.restorationId}) : super(key: key);
+
+  final String restorationId;
+
+  @override
+  Widget build(BuildContext context) {
+    return RestorationScope(
+      restorationId: restorationId,
+      child: CupertinoTabScaffold(
+        restorationId: 'scaffold',
+        tabBar: CupertinoTabBar(items: [
+          BottomNavigationBarItem(
+            icon: Icon(CupertinoIcons.home),
+            label: 'Home',
+          ),
+          BottomNavigationBarItem(
+            icon: Icon(CupertinoIcons.book),
+            label: 'My Garden',
+          ),
+          BottomNavigationBarItem(
+            icon: Icon(CupertinoIcons.search),
+            label: 'Search',
+          ),
+          BottomNavigationBarItem(
+            icon: Icon(CupertinoIcons.settings),
+            label: 'Settings',
+          ),
+        ]),
+        tabBuilder: (context, index) {
+          if (index == 0) {
+            return ListScreen(restorationId: 'list');
+          } else if (index == 1) {
+            return FavoritesScreen(restorationId: 'favorites');
+          } else if (index == 2) {
+            return SearchScreen(restorationId: 'search');
+          } else {
+            return SettingsScreen(restorationId: 'settings');
+          }
+        },
+      ),
+    );
+  }
+}

veggieseasons/lib/screens/list.dart → experimental/veggieseasons/lib/screens/list.dart

@@ -13,6 +13,10 @@ import 'package:veggieseasons/styles.dart';
 import 'package:veggieseasons/widgets/veggie_card.dart';
 
 class ListScreen extends StatelessWidget {
+  ListScreen({this.restorationId, Key key}) : super(key: key);
+
+  final String restorationId;
+
   Widget _generateVeggieRow(Veggie veggie, Preferences prefs,
       {bool inSeason = true}) {
     return Padding(
@@ -29,6 +33,7 @@ class ListScreen extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     return CupertinoTabView(
+      restorationScopeId: restorationId,
       builder: (context) {
         var dateString = DateFormat('MMMM y').format(DateTime.now());
 
@@ -38,6 +43,7 @@ class ListScreen extends StatelessWidget {
         return SafeArea(
           bottom: false,
           child: ListView.builder(
+            restorationId: 'list',
             itemCount: appState.allVeggies.length + 2,
             itemBuilder: (context, index) {
               if (index == 0) {