Add a LocaleQuery widget that can be used to fetch locale-specific data

Users of MaterialApp can provide an onLocaleChanged handler that will be
called to asynchronously fetch locale-specific data.  MaterialApp will
then instantiate a LocaleQuery that supplies the locale data to its
descendants.

examples/stocks/lib/main.dart

@@ -94,6 +94,14 @@ class StocksAppState extends State<StocksApp> {
     return null;
   }
 
+  Future<LocaleQueryData> _onLocaleChanged(ui.Locale locale) {
+    String localeString = locale.toString();
+    return initializeMessages(localeString).then((_) {
+      Intl.defaultLocale = localeString;
+      return StockStrings.instance;
+    });
+  }
+
   Widget build(BuildContext context) {
     return new MaterialApp(
       title: 'Stocks',
@@ -102,13 +110,12 @@ class StocksAppState extends State<StocksApp> {
          '/':         (RouteArguments args) => new StockHome(_stocks, _symbols, _optimismSetting, modeUpdater),
          '/settings': (RouteArguments args) => new StockSettings(_optimismSetting, _backupSetting, settingsUpdater)
       },
-      onGenerateRoute: _getRoute
+      onGenerateRoute: _getRoute,
+      onLocaleChanged: _onLocaleChanged
     );
   }
 }
 
 void main() {
-  initializeMessages(Intl.defaultLocale).then((_) {
-    runApp(new StocksApp());
-  });
+  runApp(new StocksApp());
 }

examples/stocks/lib/stock_home.dart

@@ -147,7 +147,7 @@ class StockHomeState extends State<StockHome> {
   Widget buildToolBar() {
     return new ToolBar(
       elevation: 0,
-      center: new Text(StockStrings.title()),
+      center: new Text(StockStrings.of(context).title()),
       right: <Widget>[
         new IconButton(
           icon: "action/search",
@@ -161,8 +161,9 @@ class StockHomeState extends State<StockHome> {
       tabBar: new TabBar(
         selection: _tabBarSelection,
         labels: <TabLabel>[
-          new TabLabel(text: StockStrings.market()),
-          new TabLabel(text: StockStrings.portfolio())]
+          new TabLabel(text: StockStrings.of(context).market()),
+          new TabLabel(text: StockStrings.of(context).portfolio())
+        ]
       )
     );
   }

examples/stocks/lib/stock_strings.dart

@@ -8,20 +8,26 @@ part of stocks;
 // To generate the stock_messages_*.dart files from the ARB files, run:
 //   pub run intl:generate_from_arb --output-dir=lib/i18n --generated-file-prefix=stock_ --no-use-deferred-loading lib/stock_strings.dart lib/i18n/stocks_*.arb
 
-class StockStrings {
-  static String title() => Intl.message(
+class StockStrings extends LocaleQueryData {
+  static StockStrings of(BuildContext context) {
+    return LocaleQuery.of(context);
+  }
+
+  static final StockStrings instance = new StockStrings();
+
+  String title() => Intl.message(
     'Stocks',
     name: 'title',
     desc: 'Title for the Stocks application'
   );
 
-  static String market() => Intl.message(
+  String market() => Intl.message(
     'MARKET',
     name: 'market',
     desc: 'Label for the Market tab'
   );
 
-  static String portfolio() => Intl.message(
+  String portfolio() => Intl.message(
     'PORTFOLIO',
     name: 'portfolio',
     desc: 'Label for the Portfolio tab'

packages/flutter/lib/src/material/material_app.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:async';
 import 'dart:ui' as ui;
 
 import 'package:flutter/rendering.dart';
@@ -37,13 +38,16 @@ class RouteArguments {
 }
 typedef Widget RouteBuilder(RouteArguments args);
 
+typedef Future<LocaleQueryData> LocaleChangedCallback(ui.Locale locale);
+
 class MaterialApp extends StatefulComponent {
   MaterialApp({
     Key key,
     this.title,
     this.theme,
     this.routes: const <String, RouteBuilder>{},
-    this.onGenerateRoute
+    this.onGenerateRoute,
+    this.onLocaleChanged
   }) : super(key: key) {
     assert(routes != null);
     assert(routes.containsKey(Navigator.defaultRouteName) || onGenerateRoute != null);
@@ -53,6 +57,7 @@ class MaterialApp extends StatefulComponent {
   final ThemeData theme;
   final Map<String, RouteBuilder> routes;
   final RouteFactory onGenerateRoute;
+  final LocaleChangedCallback onLocaleChanged;
 
   _MaterialAppState createState() => new _MaterialAppState();
 }
@@ -62,11 +67,13 @@ class _MaterialAppState extends State<MaterialApp> implements BindingObserver {
   GlobalObjectKey _navigator;
 
   Size _size;
+  LocaleQueryData _localeData;
 
   void initState() {
     super.initState();
     _navigator = new GlobalObjectKey(this);
     _size = ui.window.size;
+    didChangeLocale(ui.window.locale);
     FlutterBinding.instance.addObserver(this);
   }
 
@@ -88,6 +95,15 @@ class _MaterialAppState extends State<MaterialApp> implements BindingObserver {
 
   void didChangeSize(Size size) => setState(() { _size = size; });
 
+  void didChangeLocale(ui.Locale locale) {
+    if (config.onLocaleChanged != null) {
+      config.onLocaleChanged(locale).then((LocaleQueryData data) {
+        if (mounted)
+          setState(() { _localeData = data; });
+      });
+    }
+  }
+
   final HeroController _heroController = new HeroController();
 
   Route _generateRoute(NamedRouteSettings settings) {
@@ -106,23 +122,32 @@ class _MaterialAppState extends State<MaterialApp> implements BindingObserver {
   }
 
   Widget build(BuildContext context) {
+    if (config.onLocaleChanged != null && _localeData == null) {
+      // If the app expects a locale but we don't yet know the locale, then
+      // don't build the widgets now.
+      return new Container();
+    }
+
     ThemeData theme = config.theme ?? new ThemeData.fallback();
     return new MediaQuery(
       data: new MediaQueryData(size: _size),
-      child: new Theme(
-        data: theme,
-        child: new DefaultTextStyle(
-          style: _errorTextStyle,
-          child: new DefaultAssetBundle(
-            bundle: _defaultBundle,
-            child: new Title(
-              title: config.title,
-              color: theme.primaryColor,
-              child: new Navigator(
-                key: _navigator,
-                initialRoute: ui.window.defaultRouteName,
-                onGenerateRoute: _generateRoute,
-                observer: _heroController
+      child: new LocaleQuery(
+        data: _localeData,
+        child: new Theme(
+          data: theme,
+          child: new DefaultTextStyle(
+            style: _errorTextStyle,
+            child: new DefaultAssetBundle(
+              bundle: _defaultBundle,
+              child: new Title(
+                title: config.title,
+                color: theme.primaryColor,
+                child: new Navigator(
+                  key: _navigator,
+                  initialRoute: ui.window.defaultRouteName,
+                  onGenerateRoute: _generateRoute,
+                  observer: _heroController
+                )
               )
             )
           )

packages/flutter/lib/src/rendering/binding.dart

@@ -197,6 +197,7 @@ class _PointerEventConverter {
 class BindingObserver {
   bool didPopRoute() => false;
   void didChangeSize(Size size) { }
+  void didChangeLocale(ui.Locale locale) { }
 }
 
 /// The glue between the render tree and the Flutter engine
@@ -208,6 +209,7 @@ class FlutterBinding extends HitTestTarget {
 
     ui.window.onPointerPacket = _handlePointerPacket;
     ui.window.onMetricsChanged = _handleMetricsChanged;
+    ui.window.onLocaleChanged = _handleLocaleChanged;
     ui.window.onPopRoute = _handlePopRoute;
 
     if (renderViewOverride == null) {
@@ -244,6 +246,11 @@ class FlutterBinding extends HitTestTarget {
       observer.didChangeSize(size);
   }
 
+  void _handleLocaleChanged() {
+    for (BindingObserver observer in _observers)
+      observer.didChangeLocale(ui.window.locale);
+  }
+
   void _handlePersistentFrameCallback(Duration timeStamp) {
     beginFrame();
   }

packages/flutter/lib/src/widgets/locale_query.dart

@@ -0,0 +1,32 @@
+// Copyright 2015 The Chromium 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 'framework.dart';
+
+// Superclass for locale-specific data provided by the application.
+class LocaleQueryData { }
+
+class LocaleQuery<T extends LocaleQueryData> extends InheritedWidget {
+  LocaleQuery({
+    Key key,
+    this.data,
+    Widget child
+  }) : super(key: key, child: child) {
+    assert(child != null);
+  }
+
+  final T data;
+
+  static LocaleQueryData of(BuildContext context) {
+    LocaleQuery query = context.inheritFromWidgetOfType(LocaleQuery);
+    return query == null ? null : query.data;
+  }
+
+  bool updateShouldNotify(LocaleQuery old) => data != old.data;
+
+  void debugFillDescription(List<String> description) {
+    super.debugFillDescription(description);
+    description.add('$data');
+  }
+}

packages/flutter/lib/widgets.dart

@@ -19,6 +19,7 @@ export 'src/widgets/gesture_detector.dart';
 export 'src/widgets/gridpaper.dart';
 export 'src/widgets/heroes.dart';
 export 'src/widgets/homogeneous_viewport.dart';
+export 'src/widgets/locale_query.dart';
 export 'src/widgets/media_query.dart';
 export 'src/widgets/mimic.dart';
 export 'src/widgets/mixed_viewport.dart';

packages/flutter/pubspec.yaml

@@ -7,8 +7,8 @@ dependencies:
   collection: '>=1.1.3 <2.0.0'
   intl: '>=0.12.4+2 <0.13.0'
   material_design_icons: '>=0.0.3 <0.1.0'
-  sky_engine: 0.0.67
-  sky_services: 0.0.67
+  sky_engine: 0.0.68
+  sky_services: 0.0.68
   vector_math: '>=1.4.3 <2.0.0'
 
   # To pin the transitive dependency through mojo_sdk.