Provide a way to override global InheritedWidgets (#14348)

For example, so that the gallery can override the media query globally.

examples/flutter_gallery/lib/gallery/app.dart

@@ -51,6 +51,7 @@ class GalleryAppState extends State<GalleryApp> {
   bool _showPerformanceOverlay = false;
   bool _checkerboardRasterCacheImages = false;
   bool _checkerboardOffscreenLayers = false;
+  TextDirection _overrideDirection = TextDirection.ltr;
   double _timeDilation = 1.0;
   TargetPlatform _platform;
 
@@ -139,6 +140,12 @@ class GalleryAppState extends State<GalleryApp> {
           _textScaleFactor = value;
         });
       },
+      overrideDirection: _overrideDirection,
+      onOverrideDirectionChanged: (TextDirection value) {
+        setState(() {
+          _overrideDirection = value;
+        });
+      },
       onSendFeedback: widget.onSendFeedback,
     );
 
@@ -155,7 +162,7 @@ class GalleryAppState extends State<GalleryApp> {
       // using named routes, consider the example in the Navigator class documentation:
       // https://docs.flutter.io/flutter/widgets/Navigator-class.html
       _kRoutes[item.routeName] = (BuildContext context) {
-        return _applyScaleFactor(item.buildRoute(context));
+        return item.buildRoute(context);
       };
     }
 
@@ -168,6 +175,12 @@ class GalleryAppState extends State<GalleryApp> {
       checkerboardOffscreenLayers: _checkerboardOffscreenLayers,
       routes: _kRoutes,
       home: _applyScaleFactor(home),
+      builder: (BuildContext context, Widget child) {
+        return new Directionality(
+          textDirection: _overrideDirection,
+          child: _applyScaleFactor(child),
+        );
+      },
     );
   }
 }

examples/flutter_gallery/lib/gallery/drawer.dart

@@ -120,6 +120,8 @@ class GalleryDrawer extends StatelessWidget {
     this.checkerboardOffscreenLayers,
     this.onCheckerboardOffscreenLayersChanged,
     this.onPlatformChanged,
+    this.overrideDirection: TextDirection.ltr,
+    this.onOverrideDirectionChanged,
     this.onSendFeedback,
   }) : assert(onThemeChanged != null),
        assert(onTimeDilationChanged != null),
@@ -145,6 +147,9 @@ class GalleryDrawer extends StatelessWidget {
 
   final ValueChanged<TargetPlatform> onPlatformChanged;
 
+  final TextDirection overrideDirection;
+  final ValueChanged<TextDirection> onOverrideDirectionChanged;
+
   final VoidCallback onSendFeedback;
 
   @override
@@ -220,6 +225,16 @@ class GalleryDrawer extends StatelessWidget {
       selected: timeDilation != 1.0,
     );
 
+    final Widget overrideDirectionItem = new CheckboxListTile(
+      title: const Text('Force RTL'),
+      value: overrideDirection == TextDirection.rtl,
+      onChanged: (bool value) {
+        onOverrideDirectionChanged(value ? TextDirection.rtl : TextDirection.ltr);
+      },
+      secondary: const Icon(Icons.format_textdirection_r_to_l),
+      selected: overrideDirection == TextDirection.rtl,
+    );
+
     final Widget sendFeedbackItem = new ListTile(
       leading: const Icon(Icons.report),
       title: const Text('Send feedback'),
@@ -285,6 +300,7 @@ class GalleryDrawer extends StatelessWidget {
     allDrawerItems.addAll(textSizeItems);
 
     allDrawerItems..addAll(<Widget>[
+      overrideDirectionItem,
       const Divider(),
       animateSlowlyItem,
       const Divider(),

examples/flutter_gallery/lib/gallery/home.dart

@@ -77,6 +77,8 @@ class GalleryHome extends StatefulWidget {
     this.checkerboardOffscreenLayers,
     this.onCheckerboardOffscreenLayersChanged,
     this.onPlatformChanged,
+    this.overrideDirection: TextDirection.ltr,
+    this.onOverrideDirectionChanged,
     this.onSendFeedback,
   }) : assert(onThemeChanged != null),
        assert(onTimeDilationChanged != null),
@@ -102,6 +104,9 @@ class GalleryHome extends StatefulWidget {
 
   final ValueChanged<TargetPlatform> onPlatformChanged;
 
+  final TextDirection overrideDirection;
+  final ValueChanged<TextDirection> onOverrideDirectionChanged;
+
   final VoidCallback onSendFeedback;
 
   @override
@@ -177,6 +182,8 @@ class GalleryHomeState extends State<GalleryHome> with SingleTickerProviderState
         checkerboardOffscreenLayers: widget.checkerboardOffscreenLayers,
         onCheckerboardOffscreenLayersChanged: widget.onCheckerboardOffscreenLayersChanged,
         onPlatformChanged: widget.onPlatformChanged,
+        overrideDirection: widget.overrideDirection,
+        onOverrideDirectionChanged: widget.onOverrideDirectionChanged,
         onSendFeedback: widget.onSendFeedback,
       ),
       body: new CustomScrollView(

examples/flutter_gallery/test/drawer_test.dart

@@ -69,7 +69,7 @@ void main() {
     expect(newTextSize, equals(origTextSize));
 
     // Scroll to the bottom of the menu.
-    await tester.drag(find.text('Small'), const Offset(0.0, -450.0));
+    await tester.drag(find.text('Small'), const Offset(0.0, -1000.0));
     await tester.pump();
     await tester.pump(const Duration(seconds: 1)); // Wait until it's changed.
 

examples/flutter_gallery/test/smoke_test.dart

@@ -159,7 +159,7 @@ Future<Null> runSmokeTest(WidgetTester tester) async {
   await tester.pump(const Duration(seconds: 1)); // Wait until it's changed.
 
   // Scroll the 'Send feedback' item into view.
-  await tester.drag(find.text('Small'), const Offset(0.0, -450.0));
+  await tester.drag(find.text('Small'), const Offset(0.0, -1000.0));
   await tester.pump();
   await tester.pump(const Duration(seconds: 1)); // Wait until it's changed.
 

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

@@ -3557,6 +3557,14 @@ typedef Widget WidgetBuilder(BuildContext context);
 /// Used by [ListView.builder] and other APIs that use lazily-generated widgets.
 typedef Widget IndexedWidgetBuilder(BuildContext context, int index);
 
+/// A builder that builds a widget given a child.
+///
+/// The child should typically be part of the returned widget tree.
+///
+/// Used by [AnimatedBuilder.builder], as well as [WidgetsApp.builder] and
+/// [MaterialApp.builder].
+typedef Widget TransitionBuilder(BuildContext context, Widget child);
+
 /// An [Element] that composes other [Element]s.
 ///
 /// Rather than creating a [RenderObject] directly, a [ComponentElement] creates

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

@@ -527,13 +527,6 @@ class AlignTransition extends AnimatedWidget {
   }
 }
 
-/// A builder that builds a widget given a child.
-///
-/// The child should typically be part of the returned widget tree.
-///
-/// Used by [AnimatedBuilder.builder].
-typedef Widget TransitionBuilder(BuildContext context, Widget child);
-
 /// A general-purpose widget for building animations.
 ///
 /// AnimatedBuilder is useful for more complex widgets that wish to include

packages/flutter/test/material/app_builder_test.dart

+// Copyright 2018 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 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/material.dart';
+
+void main() {
+  testWidgets('builder doesn\'t get called if app doesn\'t change', (WidgetTester tester) async {
+    final List<String> log = <String>[];
+    final Widget app = new MaterialApp(
+      theme: new ThemeData(
+        primarySwatch: Colors.green,
+      ),
+      home: const Placeholder(),
+      builder: (BuildContext context, Widget child) {
+        log.add('build');
+        expect(Theme.of(context).primaryColor, Colors.green.shade500);
+        expect(Directionality.of(context), TextDirection.ltr);
+        expect(child, const isInstanceOf<Navigator>());
+        return const Placeholder();
+      },
+    );
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.rtl,
+        child: app,
+      ),
+    );
+    expect(log, <String>['build']);
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.ltr,
+        child: app,
+      ),
+    );
+    expect(log, <String>['build']);
+  });
+
+  testWidgets('builder doesn\'t get called if app doesn\'t change', (WidgetTester tester) async {
+    final List<String> log = <String>[];
+    await tester.pumpWidget(
+      new MaterialApp(
+        theme: new ThemeData(
+          primarySwatch: Colors.yellow,
+        ),
+        home: new Builder(
+          builder: (BuildContext context) {
+            log.add('build');
+            expect(Theme.of(context).primaryColor, Colors.yellow.shade500);
+            expect(Directionality.of(context), TextDirection.rtl);
+            return const Placeholder();
+          },
+        ),
+        builder: (BuildContext context, Widget child) {
+          return new Directionality(
+            textDirection: TextDirection.rtl,
+            child: child,
+          );
+        },
+      ),
+    );
+    expect(log, <String>['build']);
+  });
+}