Track scroll position

- Change RouteArguments to pass the route's BuildContext rather than
  the Navigator. This caused the bulk of the examples/ and .../test/
  changes (those are mostly mechanical changes). It also meant I could
  simplify Navigator.of().

- Make initState() actually get called when the State's Element is in
  the tree, so you can use Foo.of() functions there. Added a test for
  this also.

- Provide a RouteWidget so that routes have a position in the Widget
  tree. The bulk of the route logic is still in a longer-lived Route
  object for now.

- Make Route.setState() only rebuild the actual route, not the whole
  navigator.

- Provided a Route.of().

- Provided a Route.writeState / Route.readState API that tries to
  identify the clients by their runtimeType, their key, and their
  ancestors keys, up to the nearest ancestor with a GlobalKey.

- Made scrollables hook into this API to track state. Added a test to
  make sure this works.

- Fix the debug output of GestureDetector and the hashCode of
  MixedViewport.

- Fixed ScrollableWidgetListState<T> to handle infinite lists.

examples/fitness/lib/feed.dart

@@ -44,9 +44,8 @@ class DialogMenuItem extends StatelessComponent {
 }
 
 class FeedFragment extends StatefulComponent {
-  FeedFragment({ this.navigator, this.userData, this.onItemCreated, this.onItemDeleted });
+  FeedFragment({ this.userData, this.onItemCreated, this.onItemDeleted });
 
-  final NavigatorState navigator;
   final UserData userData;
   final FitnessItemHandler onItemCreated;
   final FitnessItemHandler onItemDeleted;
@@ -62,7 +61,7 @@ class FeedFragmentState extends State<FeedFragment> {
     setState(() {
       _fitnessMode = value;
     });
-    config.navigator.pop();
+    Navigator.of(context).pop();
   }
 
   void _showDrawer() {
@@ -93,8 +92,8 @@ class FeedFragmentState extends State<FeedFragment> {
   }
 
   void _handleShowSettings() {
-    config.navigator.pop();
-    config.navigator.pushNamed('/settings');
+    Navigator.of(context)..pop()
+                         ..pushNamed('/settings');
   }
 
   // TODO(jackson): We should be localizing
@@ -122,7 +121,7 @@ class FeedFragmentState extends State<FeedFragment> {
       content: new Text("Item deleted."),
       actions: <SnackBarAction>[new SnackBarAction(label: "UNDO", onPressed: () {
         config.onItemCreated(item);
-        config.navigator.pop();
+        Navigator.of(context).pop();
       })]
     );
   }
@@ -193,7 +192,7 @@ class FeedFragmentState extends State<FeedFragment> {
   void _handleActionButtonPressed() {
     showDialog(context: context, child: new AddItemDialog()).then((routeName) {
       if (routeName != null)
-        config.navigator.pushNamed(routeName);
+        Navigator.of(context).pushNamed(routeName);
     });
   }
 

examples/fitness/lib/main.dart

@@ -135,7 +135,6 @@ class FitnessAppState extends State<FitnessApp> {
       routes: <String, RouteBuilder>{
         '/': (RouteArguments args) {
           return new FeedFragment(
-            navigator: args.navigator,
             userData: _userData,
             onItemCreated: _handleItemCreated,
             onItemDeleted: _handleItemDeleted
@@ -143,19 +142,16 @@ class FitnessAppState extends State<FitnessApp> {
         },
         '/meals/new': (RouteArguments args) {
           return new MealFragment(
-            navigator: args.navigator,
             onCreated: _handleItemCreated
           );
         },
         '/measurements/new': (RouteArguments args) {
           return new MeasurementFragment(
-            navigator: args.navigator,
             onCreated: _handleItemCreated
           );
         },
         '/settings': (RouteArguments args) {
           return new SettingsFragment(
-            navigator: args.navigator,
             userData: _userData,
             updater: settingsUpdater
           );

examples/fitness/lib/meal.dart

@@ -43,9 +43,8 @@ class MealRow extends FitnessItemRow {
 }
 
 class MealFragment extends StatefulComponent {
-  MealFragment({ this.navigator, this.onCreated });
+  MealFragment({ this.onCreated });
 
-  NavigatorState navigator;
   FitnessItemHandler onCreated;
 
   MealFragmentState createState() => new MealFragmentState();
@@ -56,14 +55,14 @@ class MealFragmentState extends State<MealFragment> {
 
   void _handleSave() {
     config.onCreated(new Meal(when: new DateTime.now(), description: _description));
-    config.navigator.pop();
+    Navigator.of(context).pop();
   }
 
   Widget buildToolBar() {
     return new ToolBar(
       left: new IconButton(
         icon: "navigation/close",
-        onPressed: config.navigator.pop),
+        onPressed: Navigator.of(context).pop),
       center: new Text('New Meal'),
       right: <Widget>[
         // TODO(abarth): Should this be a FlatButton?

examples/fitness/lib/measurement.dart

@@ -104,9 +104,8 @@ class MeasurementDateDialogState extends State<MeasurementDateDialog> {
 }
 
 class MeasurementFragment extends StatefulComponent {
-  MeasurementFragment({ this.navigator, this.onCreated });
+  MeasurementFragment({ this.onCreated });
 
-  final NavigatorState navigator;
   final FitnessItemHandler onCreated;
 
   MeasurementFragmentState createState() => new MeasurementFragmentState();
@@ -131,14 +130,14 @@ class MeasurementFragmentState extends State<MeasurementFragment> {
       );
     }
     config.onCreated(new Measurement(when: _when, weight: parsedWeight));
-    config.navigator.pop();
+    Navigator.of(context).pop();
   }
 
   Widget buildToolBar() {
     return new ToolBar(
       left: new IconButton(
         icon: "navigation/close",
-        onPressed: config.navigator.pop),
+        onPressed: Navigator.of(context).pop),
       center: new Text('New Measurement'),
       right: <Widget>[
         // TODO(abarth): Should this be a FlatButton?

examples/fitness/lib/settings.dart

@@ -10,9 +10,8 @@ typedef void SettingsUpdater({
 });
 
 class SettingsFragment extends StatefulComponent {
-  SettingsFragment({ this.navigator, this.userData, this.updater });
+  SettingsFragment({ this.userData, this.updater });
 
-  final NavigatorState navigator;
   final UserData userData;
   final SettingsUpdater updater;
 
@@ -29,7 +28,7 @@ class SettingsFragmentState extends State<SettingsFragment> {
     return new ToolBar(
       left: new IconButton(
         icon: "navigation/arrow_back",
-        onPressed: config.navigator.pop
+        onPressed: () => Navigator.of(context).pop()
       ),
       center: new Text('Settings')
     );
@@ -48,7 +47,7 @@ class SettingsFragmentState extends State<SettingsFragment> {
   void _handleGoalWeightChanged(String goalWeight) {
     // TODO(jackson): Looking for null characters to detect enter key is a hack
     if (goalWeight.endsWith("\u{0}")) {
-      config.navigator.pop(double.parse(goalWeight.replaceAll("\u{0}", "")));
+      Navigator.of(context).pop(double.parse(goalWeight.replaceAll("\u{0}", "")));
     } else {
       setState(() {
         try {

examples/game/lib/main.dart

@@ -108,10 +108,10 @@ class GameDemoState extends State<GameDemo> {
                 _sounds,
                 (int lastScore) {
                   setState(() { _lastScore = lastScore; });
-                  args.navigator.pop();
+                  Navigator.of(args.context).pop();
                 }
               );
-              args.navigator.pushNamed('/game');
+              Navigator.of(args.context).pushNamed('/game');
             },
             texture: _spriteSheetUI['btn_play_up.png'],
             textureDown: _spriteSheetUI['btn_play_down.png'],

examples/stocks/lib/main.dart

@@ -92,8 +92,8 @@ class StocksAppState extends State<StocksApp> {
       title: 'Stocks',
       theme: theme,
       routes: <String, RouteBuilder>{
-         '/':         (RouteArguments args) => new StockHome(args.navigator, _stocks, _symbols, _optimismSetting, modeUpdater),
-         '/settings': (RouteArguments args) => new StockSettings(args.navigator, _optimismSetting, _backupSetting, settingsUpdater)
+         '/':         (RouteArguments args) => new StockHome(_stocks, _symbols, _optimismSetting, modeUpdater),
+         '/settings': (RouteArguments args) => new StockSettings(_optimismSetting, _backupSetting, settingsUpdater)
       },
       onGenerateRoute: _getRoute
     );

examples/stocks/lib/stock_home.dart

@@ -7,9 +7,8 @@ part of stocks;
 typedef void ModeUpdater(StockMode mode);
 
 class StockHome extends StatefulComponent {
-  StockHome(this.navigator, this.stocks, this.symbols, this.stockMode, this.modeUpdater);
+  StockHome(this.stocks, this.symbols, this.stockMode, this.modeUpdater);
 
-  final NavigatorState navigator;
   final Map<String, Stock> stocks;
   final List<String> symbols;
   final StockMode stockMode;
@@ -25,7 +24,7 @@ class StockHomeState extends State<StockHome> {
   String _searchQuery;
 
   void _handleSearchBegin() {
-    config.navigator.pushState(this, (_) {
+    Navigator.of(context).pushState(this, (_) {
       setState(() {
         _isSearching = false;
         _searchQuery = null;
@@ -38,10 +37,10 @@ class StockHomeState extends State<StockHome> {
 
   void _handleSearchEnd() {
     assert(() {
-      final StateRoute currentRoute = config.navigator.currentRoute;
+      final StateRoute currentRoute = Navigator.of(context).currentRoute;
       return currentRoute.owner == this;
     });
-    config.navigator.pop();
+    Navigator.of(context).pop();
   }
 
   void _handleSearchQueryChanged(String query) {
@@ -92,13 +91,13 @@ class StockHomeState extends State<StockHome> {
                   new FlatButton(
                     child: new Text('USE IT'),
                     onPressed: () {
-                      config.navigator.pop(false);
+                      Navigator.of(context).pop(false);
                     }
                   ),
                   new FlatButton(
                     child: new Text('OH WELL'),
                     onPressed: () {
-                      config.navigator.pop(false);
+                      Navigator.of(context).pop(false);
                     }
                   ),
                 ]
@@ -142,8 +141,8 @@ class StockHomeState extends State<StockHome> {
   }
 
   void _handleShowSettings() {
-    config.navigator.pop();
-    config.navigator.pushNamed('/settings');
+    Navigator.of(context)..pop()
+                         ..pushNamed('/settings');
   }
 
   Widget buildToolBar() {
@@ -193,7 +192,7 @@ class StockHomeState extends State<StockHome> {
       onOpen: (Stock stock, Key arrowKey) {
         Set<Key> mostValuableKeys = new Set<Key>();
         mostValuableKeys.add(arrowKey);
-        config.navigator.pushNamed('/stock/${stock.symbol}', mostValuableKeys: mostValuableKeys);
+        Navigator.of(context).pushNamed('/stock/${stock.symbol}', mostValuableKeys: mostValuableKeys);
       }
     );
   }
@@ -239,7 +238,7 @@ class StockHomeState extends State<StockHome> {
   }
 
   void _handleUndo() {
-    config.navigator.pop();
+    Navigator.of(context).pop();
   }
 
   void _handleStockPurchased() {

examples/stocks/lib/stock_settings.dart

@@ -10,9 +10,8 @@ typedef void SettingsUpdater({
 });
 
 class StockSettings extends StatefulComponent {
-  const StockSettings(this.navigator, this.optimism, this.backup, this.updater);
+  const StockSettings(this.optimism, this.backup, this.updater);
 
-  final NavigatorState navigator;
   final StockMode optimism;
   final BackupMode backup;
   final SettingsUpdater updater;
@@ -41,19 +40,19 @@ class StockSettingsState extends State<StockSettings> {
             title: new Text("Change mode?"),
             content: new Text("Optimistic mode means everything is awesome. Are you sure you can handle that?"),
             onDismiss: () {
-              config.navigator.pop(false);
+              Navigator.of(context).pop(false);
             },
             actions: <Widget>[
               new FlatButton(
                 child: new Text('NO THANKS'),
                 onPressed: () {
-                  config.navigator.pop(false);
+                  Navigator.of(context).pop(false);
                 }
               ),
               new FlatButton(
                 child: new Text('AGREE'),
                 onPressed: () {
-                  config.navigator.pop(true);
+                  Navigator.of(context).pop(true);
                 }
               ),
             ]
@@ -75,7 +74,7 @@ class StockSettingsState extends State<StockSettings> {
     return new ToolBar(
       left: new IconButton(
         icon: 'navigation/arrow_back',
-        onPressed: config.navigator.pop
+        onPressed: () => Navigator.of(context).pop()
       ),
       center: new Text('Settings')
     );

examples/widgets/drag_and_drop.dart

@@ -65,8 +65,7 @@ class Dot extends StatelessComponent {
 }
 
 class ExampleDragSource extends StatelessComponent {
-  ExampleDragSource({ Key key, this.navigator, this.name, this.color }) : super(key: key);
-  final NavigatorState navigator;
+  ExampleDragSource({ Key key, this.name, this.color }) : super(key: key);
   final String name;
   final Color color;
 
@@ -75,7 +74,6 @@ class ExampleDragSource extends StatelessComponent {
 
   Widget build(BuildContext context) {
     return new Draggable(
-      navigator: navigator,
       data: new DragData(name),
       child: new Dot(color: color, size: kDotSize),
       feedback: new Transform(
@@ -91,13 +89,7 @@ class ExampleDragSource extends StatelessComponent {
   }
 }
 
-class DragAndDropApp extends StatefulComponent {
-  DragAndDropApp({ this.navigator });
-  final NavigatorState navigator;
-  DragAndDropAppState createState() => new DragAndDropAppState();
-}
-
-class DragAndDropAppState extends State<DragAndDropApp> {
+class DragAndDropApp extends StatelessComponent {
   Widget build(BuildContext context) {
     return new Scaffold(
       toolBar: new ToolBar(
@@ -107,9 +99,9 @@ class DragAndDropAppState extends State<DragAndDropApp> {
         style: Theme.of(context).text.body1.copyWith(textAlign: TextAlign.center),
         child: new Column(<Widget>[
           new Flexible(child: new Row(<Widget>[
-              new ExampleDragSource(navigator: config.navigator, name: 'Orange', color: const Color(0xFFFF9000)),
-              new ExampleDragSource(navigator: config.navigator, name: 'Teal', color: const Color(0xFF00FFFF)),
-              new ExampleDragSource(navigator: config.navigator, name: 'Yellow', color: const Color(0xFFFFF000)),
+              new ExampleDragSource(name: 'Orange', color: const Color(0xFFFF9000)),
+              new ExampleDragSource(name: 'Teal', color: const Color(0xFF00FFFF)),
+              new ExampleDragSource(name: 'Yellow', color: const Color(0xFFFFF000)),
             ],
             alignItems: FlexAlignItems.center,
             justifyContent: FlexJustifyContent.spaceAround
@@ -130,7 +122,7 @@ void main() {
   runApp(new MaterialApp(
     title: 'Drag and Drop Flutter Demo',
     routes: <String, RouteBuilder>{
-     '/': (RouteArguments args) => new DragAndDropApp(navigator: args.navigator)
+     '/': (RouteArguments args) => new DragAndDropApp()
     }
   ));
 }

examples/widgets/navigation.dart

@@ -12,11 +12,11 @@ final Map<String, RouteBuilder> routes = <String, RouteBuilder>{
       new Text("You are at home"),
       new RaisedButton(
         child: new Text('GO SHOPPING'),
-        onPressed: () => args.navigator.pushNamed('/shopping')
+        onPressed: () => Navigator.of(args.context).pushNamed('/shopping')
       ),
       new RaisedButton(
         child: new Text('START ADVENTURE'),
-        onPressed: () => args.navigator.pushNamed('/adventure')
+        onPressed: () => Navigator.of(args.context).pushNamed('/adventure')
       )],
       justifyContent: FlexJustifyContent.center
     )
@@ -28,11 +28,11 @@ final Map<String, RouteBuilder> routes = <String, RouteBuilder>{
       new Text("Village Shop"),
       new RaisedButton(
         child: new Text('RETURN HOME'),
-        onPressed: () => args.navigator.pop()
+        onPressed: () => Navigator.of(args.context).pop()
       ),
       new RaisedButton(
         child: new Text('GO TO DUNGEON'),
-        onPressed: () => args.navigator.pushNamed('/adventure')
+        onPressed: () => Navigator.of(args.context).pushNamed('/adventure')
       )],
       justifyContent: FlexJustifyContent.center
     )
@@ -44,7 +44,7 @@ final Map<String, RouteBuilder> routes = <String, RouteBuilder>{
       new Text("Monster's Lair"),
       new RaisedButton(
         child: new Text('RUN!!!'),
-        onPressed: () => args.navigator.pop()
+        onPressed: () => Navigator.of(args.context).pop()
       )],
       justifyContent: FlexJustifyContent.center
     )

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

@@ -26,7 +26,7 @@ class IconTheme extends InheritedWidget {
   bool updateShouldNotify(IconTheme old) => data != old.data;
 
   void debugFillDescription(List<String> description) {
-  super.debugFillDescription(description);
+    super.debugFillDescription(description);
     description.add('$data');
   }
 }

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

@@ -37,19 +37,16 @@ enum DragAnchor {
 class Draggable extends StatefulComponent {
   Draggable({
     Key key,
-    this.navigator,
     this.data,
     this.child,
     this.feedback,
     this.feedbackOffset: Offset.zero,
     this.dragAnchor: DragAnchor.child
   }) : super(key: key) {
-    assert(navigator != null);
     assert(child != null);
     assert(feedback != null);
   }
 
-  final NavigatorState navigator;
   final dynamic data;
   final Widget child;
   final Widget feedback;
@@ -91,12 +88,12 @@ class _DraggableState extends State<Draggable> {
       }
     );
     _route.update(point);
-    config.navigator.push(_route);
+    Navigator.of(context).push(_route);
   }
 
   void _updateDrag(PointerInputEvent event) {
     if (_route != null) {
-      config.navigator.setState(() {
+      Navigator.of(context).setState(() {
         _route.update(new Point(event.x, event.y));
       });
     }
@@ -104,7 +101,7 @@ class _DraggableState extends State<Draggable> {
 
   void _cancelDrag(PointerInputEvent event) {
     if (_route != null) {
-      config.navigator.popRoute(_route, DragEndKind.canceled);
+      Navigator.of(context).popRoute(_route, DragEndKind.canceled);
       assert(_route == null);
     }
   }
@@ -112,7 +109,7 @@ class _DraggableState extends State<Draggable> {
   void _drop(PointerInputEvent event) {
     if (_route != null) {
       _route.update(new Point(event.x, event.y));
-      config.navigator.popRoute(_route, DragEndKind.dropped);
+      Navigator.of(context).popRoute(_route, DragEndKind.dropped);
       assert(_route == null);
     }
   }

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

@@ -111,8 +111,9 @@ class Focus extends StatefulComponent {
     return true;
   }
 
-  // Don't call moveTo() from your build() function, it's intended to be called
-  // from event listeners, e.g. in response to a finger tap or tab key.
+  // Don't call moveTo() and moveScopeTo() from your build()
+  // functions, it's intended to be called from event listeners, e.g.
+  // in response to a finger tap or tab key.
 
   static void moveTo(BuildContext context, Widget widget) {
     assert(widget != null);
@@ -122,7 +123,7 @@ class Focus extends StatefulComponent {
       focusScope.focusState._setFocusedWidget(widget.key);
   }
 
-  static void _moveScopeTo(BuildContext context, Focus component) {
+  static void moveScopeTo(BuildContext context, Focus component) {
     assert(component != null);
     assert(component.key != null);
     _FocusScope focusScope = context.inheritedWidgetOfType(_FocusScope);
@@ -209,8 +210,6 @@ class FocusState extends State<Focus> {
 
   void initState() {
     super.initState();
-    if (config.autofocus)
-      Focus._moveScopeTo(context, config);
     _updateWidgetRemovalListener(_focusedWidget);
     _updateScopeRemovalListener(_focusedScope);
   }

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

@@ -1023,10 +1023,14 @@ abstract class ComponentElement<T extends Widget> extends BuildableElement<T> {
     super.mount(parent, newSlot);
     assert(_child == null);
     assert(_active);
-    rebuild();
+    _firstBuild();
     assert(_child != null);
   }
 
+  void _firstBuild() {
+    rebuild();
+  }
+
   /// Reinvokes the build() method of the StatelessComponent object (for
   /// stateless components) or the State object (for stateful components) and
   /// then updates the widget tree.
@@ -1098,6 +1102,13 @@ class StatefulComponentElement<T extends StatefulComponent, U extends State<T>>
     assert(_state._config == null);
     _state._config = widget;
     assert(_state._debugLifecycleState == _StateLifecycle.created);
+  }
+
+  U get state => _state;
+  U _state;
+
+  void _firstBuild() {
+    assert(_state._debugLifecycleState == _StateLifecycle.created);
     try {
       _debugSetAllowIgnoredCallsToMarkNeedsBuild(true);
       _state.initState();
@@ -1111,11 +1122,9 @@ class StatefulComponentElement<T extends StatefulComponent, U extends State<T>>
       return false;
     });
     assert(() { _state._debugLifecycleState = _StateLifecycle.ready; return true; });
+    super._firstBuild();
   }
 
-  U get state => _state;
-  U _state;
-
   void update(T newWidget) {
     super.update(newWidget);
     assert(widget == newWidget);

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

@@ -245,6 +245,7 @@ class _GestureDetectorState extends State<GestureDetector> {
   }
 
   void debugFillDescription(List<String> description) {
+    super.debugFillDescription(description);
     List<String> gestures = <String>[];
     if (_tap != null)
       gestures.add('tap');
@@ -262,7 +263,7 @@ class _GestureDetectorState extends State<GestureDetector> {
       gestures.add('pan');
     if (_scale != null)
       gestures.add('scale');
-    if (gestures.isEmpty);
+    if (gestures.isEmpty)
       gestures.add('<none>');
     description.add('gestures: ${gestures.join(", ")}');
   }

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

@@ -63,7 +63,7 @@ class _ChildKey {
     return type == typedOther.type &&
            key == typedOther.key;
   }
-  int get hashCode => 373 * 37 * type.hashCode + key.hashCode;
+  int get hashCode => ((373 * 37) + type.hashCode) * 37 + key.hashCode;
   String toString() => "_ChildKey(type: $type, key: $key)";
 }
 

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

@@ -21,8 +21,8 @@ Color debugGridColor = const Color(0x7F7F2020);
 const String kDefaultRouteName = '/';
 
 class RouteArguments {
-  const RouteArguments(this.navigator, { this.previousPerformance, this.nextPerformance });
-  final NavigatorState navigator;
+  const RouteArguments({ this.context, this.previousPerformance, this.nextPerformance });
+  final BuildContext context;
   final PerformanceView previousPerformance;
   final PerformanceView nextPerformance;
 }
@@ -49,17 +49,13 @@ class Navigator extends StatefulComponent {
 
   static NavigatorState of(BuildContext context) {
     NavigatorState result;
-    bool visitor(Element element) {
-      if (element is StatefulComponentElement) {
-        if (element.state is NavigatorState) {
-          result = element.state;
-          return false;
-        }
+    context.visitAncestorElements((Element element) {
+      if (element is StatefulComponentElement && element.state is NavigatorState) {
+        result = element.state;
+        return false;
       }
       return true;
-    }
-    if (visitor(context))
-      context.visitAncestorElements(visitor);
+    });
     return result;
   }
 
@@ -268,9 +264,9 @@ class NavigatorState extends State<Navigator> {
       if (_desiredHeroes.hasInstructions) {
         if ((_desiredHeroes.to == route || _desiredHeroes.from == route) && nextHeroPerformance == null)
           nextHeroPerformance = route.performance;
-        visibleRoutes.add(route._internalBuild(nextContentRoute, buildTargetHeroes: _desiredHeroes.to == route));
+        visibleRoutes.add(new _RouteWidget(route: route, nextRoute: nextContentRoute, buildTargetHeroes: _desiredHeroes.to == route));
       } else {
-        visibleRoutes.add(route._internalBuild(nextContentRoute));
+        visibleRoutes.add(new _RouteWidget(route: route, nextRoute: nextContentRoute));
       }
       if (route.isActuallyOpaque) {
         assert(!_desiredHeroes.hasInstructions ||
@@ -330,6 +326,82 @@ class NavigatorState extends State<Navigator> {
 
 }
 
+class _RouteWidget extends StatefulComponent {
+  _RouteWidget({
+    Route route,
+    this.nextRoute,
+    this.buildTargetHeroes: false
+  }) : route = route,
+       super(key: new ObjectKey(route)) {
+    assert(route != null);
+  }
+  final Route route;
+  final Route nextRoute;
+  final bool buildTargetHeroes;
+  _RouteWidgetState createState() => new _RouteWidgetState();
+  void debugFillDescription(List<String> description) {
+    super.debugFillDescription(description);
+    if (route.performance != null)
+      description.add('${route.performance}');
+    else
+      description.add('${route.debugLabel}');
+    if (buildTargetHeroes)
+      description.add('building target heroes this frame');
+  }
+}
+
+class _RouteWidgetState extends State<_RouteWidget> {
+  void initState() {
+    super.initState();
+    config.route._widgetState = this;
+  }
+  void dispose() {
+    config.route._widgetState = null;
+    super.dispose();
+  }
+  Widget build(BuildContext context) {
+    return config.route._internalBuild(context, config.nextRoute, buildTargetHeroes: config.buildTargetHeroes);
+  }
+}
+
+class _StorageEntryIdentifier {
+  Type clientType;
+  List<Key> keys;
+  void addKey(Key key) {
+    assert(key != null);
+    assert(key is! GlobalKey);
+    keys ??= <Key>[];
+    keys.add(key);
+  }
+  GlobalKey scopeKey;
+  bool operator ==(dynamic other) {
+    if (other is! _StorageEntryIdentifier)
+      return false;
+    final _StorageEntryIdentifier typedOther = other;
+    if (clientType != typedOther.clientType ||
+        scopeKey != typedOther.scopeKey ||
+        keys?.length != typedOther.keys?.length)
+      return false;
+    if (keys != null) {
+      for (int index = 0; index < keys.length; index += 1) {
+        if (keys[index] != typedOther.keys[index])
+          return false;
+      }
+    }
+    return true;
+  }
+  int get hashCode {
+    int value = 373;
+    value = 37 * value + clientType.hashCode;
+    value = 37 * value + scopeKey.hashCode;
+    if (keys != null) {
+      for (Key key in keys)
+        value = 37 * value + key.hashCode;
+    }
+    return value;
+  }
+}
+
 abstract class Route {
   Route() {
     _subtreeKey = new GlobalKey(label: debugLabel);
@@ -390,10 +462,13 @@ abstract class Route {
 
   NavigatorState get navigator => _navigator;
   NavigatorState _navigator;
+  _RouteWidgetState _widgetState;
 
   void setState(void fn()) {
-    assert(navigator != null);
-    navigator.setState(fn);
+    if (_widgetState != null)
+      _widgetState.setState(fn);
+    else
+      fn();
   }
 
   void didPush(NavigatorState navigator) {
@@ -419,18 +494,21 @@ abstract class Route {
     }
   }
 
-  /// Called by the navigator.build() function if hasContent is true, to get the
-  /// subtree for this route.
+  /// Called (indirectly, via a RouteWidget) by the navigator.build()
+  /// function if hasContent is true, to get the subtree for this
+  /// route.
   ///
   /// If buildTargetHeroes is true, then getHeroesToAnimate() will be called
   /// after this build, before the next build, and this build should render the
   /// route off-screen, at the end of its animation. Next frame, the argument
   /// will be false, and the tree should be built at the first frame of the
   /// transition animation, whatever that is.
-  Widget _internalBuild(Route nextRoute, { bool buildTargetHeroes: false }) {
+  Widget _internalBuild(BuildContext context, Route nextRoute, { bool buildTargetHeroes: false }) {
     assert(navigator != null);
+    assert(_widgetState != null);
+    assert(hasContent);
     return keySubtree(build(new RouteArguments(
-      navigator,
+      context: context,
       previousPerformance: performance,
       nextPerformance: nextRoute?.performance
     )));
@@ -446,12 +524,12 @@ abstract class Route {
   Map<Object, HeroHandle> getHeroesToAnimate([Set<Key> mostValuableKeys]) => const <Object, HeroHandle>{};
   bool _hasActiveHeroes = false;
 
+  GlobalKey _subtreeKey;
+
   /// Returns the BuildContext for the root of the subtree built for this route,
   /// assuming that internalBuild used keySubtree to build that subtree.
   /// This is only valid after a build phase.
-  BuildContext get context => _subtreeKey.currentContext;
-
-  GlobalKey _subtreeKey;
+  BuildContext get subtreeContext => _subtreeKey.currentContext;
 
   /// Wraps the given subtree in a route-specific GlobalKey.
   Widget keySubtree(Widget child) {
@@ -465,6 +543,52 @@ abstract class Route {
   /// change what subtree is built for this route.
   Widget build(RouteArguments args);
 
+  static Route of(BuildContext context) {
+    Route result;
+    context.visitAncestorElements((Element element) {
+      if (element is StatefulComponentElement && element.state is _RouteWidgetState) {
+        result = element.widget.route;
+        return false;
+      }
+      return true;
+    });
+    return result;
+  }
+
+  _StorageEntryIdentifier _computeStorageIdentifier(BuildContext context) {
+    _StorageEntryIdentifier result = new _StorageEntryIdentifier();
+    result.clientType = context.widget.runtimeType;
+    Key lastKey = context.widget.key;
+    if (lastKey is! GlobalKey) {
+      context.visitAncestorElements((Element element) {
+        if (element.widget.key is GlobalKey) {
+          lastKey = element.widget.key;
+          return false;
+        } else if (element.widget is Navigator) {
+          // Not quite everyone who is in a Navigator actually is in a Route.
+          // For example, the modal barrier.
+          StatefulComponentElement statefulElement = element;
+          lastKey = new GlobalObjectKey(statefulElement.state);
+          return false;
+        } else if (element.widget.key != null) {
+          result.addKey(element.widget.key);
+        }
+        return true;
+      });
+      return result;
+    }
+    assert(lastKey is GlobalKey);
+    result.scopeKey = lastKey;
+    return result;
+  }
+
+  Map<_StorageEntryIdentifier, dynamic> _storage;
+  void writeState(BuildContext context, dynamic data) {
+    _storage ??= <_StorageEntryIdentifier, dynamic>{};
+    _storage[_computeStorageIdentifier(context)] = data;
+  }
+  dynamic readState(BuildContext context) => _storage != null ? _storage[_computeStorageIdentifier(context)] : null;
+
   String get debugLabel => '$runtimeType';
 
   String toString() => '$runtimeType(performance: $performance; key: $_subtreeKey)';
@@ -487,7 +611,7 @@ abstract class PerformanceRoute extends Route {
 
   Duration get transitionDuration;
 
-  Widget _internalBuild(Route nextRoute, { bool buildTargetHeroes: false }) {
+  Widget _internalBuild(BuildContext context, Route nextRoute, { bool buildTargetHeroes: false }) {
     assert(hasContent);
     assert(transitionDuration > Duration.ZERO);
     if (buildTargetHeroes && performance.progress != 1.0) {
@@ -496,11 +620,11 @@ abstract class PerformanceRoute extends Route {
       fakePerformance.progress = 1.0;
       return new OffStage(
         child: keySubtree(
-          build(new RouteArguments(navigator, previousPerformance: fakePerformance))
+          build(new RouteArguments(context: context, previousPerformance: fakePerformance))
         )
       );
     }
-    return super._internalBuild(nextRoute, buildTargetHeroes: buildTargetHeroes);
+    return super._internalBuild(context, nextRoute, buildTargetHeroes: buildTargetHeroes);
   }
 
   void didPush(NavigatorState navigator) {
@@ -539,7 +663,7 @@ class PageRoute extends PerformanceRoute {
   Duration get transitionDuration => _kTransitionDuration;
 
   Map<Object, HeroHandle> getHeroesToAnimate([Set<Key> mostValuableKeys]) {
-    return Hero.of(context, mostValuableKeys);
+    return Hero.of(subtreeContext, mostValuableKeys);
   }
 
   Widget build(RouteArguments args) {

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

@@ -16,6 +16,7 @@ import 'framework.dart';
 import 'gesture_detector.dart';
 import 'homogeneous_viewport.dart';
 import 'mixed_viewport.dart';
+import 'navigator.dart';
 
 // The gesture velocity properties are pixels/second, config min,max limits are pixels/ms
 const double _kMillisecondsPerSecond = 1000.0;
@@ -54,15 +55,14 @@ abstract class Scrollable extends StatefulComponent {
 abstract class ScrollableState<T extends Scrollable> extends State<T> {
   void initState() {
     super.initState();
-    if (config.initialScrollOffset is double)
-      _scrollOffset = config.initialScrollOffset;
     _animation = new SimulationStepper(_setScrollOffset);
+    _scrollOffset = Route.of(context)?.readState(context) ?? config.initialScrollOffset ?? 0.0;
   }
 
   SimulationStepper _animation;
 
-  double _scrollOffset = 0.0;
   double get scrollOffset => _scrollOffset;
+  double _scrollOffset;
 
   Offset get scrollOffsetVector {
     if (config.scrollDirection == ScrollDirection.horizontal)
@@ -178,6 +178,7 @@ abstract class ScrollableState<T extends Scrollable> extends State<T> {
     setState(() {
       _scrollOffset = newScrollOffset;
     });
+    Route.of(context)?.writeState(context, _scrollOffset);
     dispatchOnScroll();
   }
 
@@ -510,8 +511,8 @@ abstract class ScrollableWidgetListState<T extends ScrollableWidgetList> extends
     }
 
     if (itemCount != _previousItemCount) {
-      scrollBehaviorUpdateNeeded = true;
       _previousItemCount = itemCount;
+      scrollBehaviorUpdateNeeded = true;
     }
 
     if (scrollBehaviorUpdateNeeded)
@@ -558,6 +559,8 @@ abstract class ScrollableWidgetListState<T extends ScrollableWidgetList> extends
   }
 
   double get _contentExtent {
+    if (itemCount == null)
+      return null;
     double contentExtent = config.itemExtent * itemCount;
     if (config.padding != null)
       contentExtent += _leadingPadding + _trailingPadding;

packages/unit/test/widget/draggable_test.dart

@@ -15,7 +15,6 @@ void main() {
         routes: <String, RouteBuilder>{
           '/': (RouteArguments args) { return new Column(<Widget>[
               new Draggable(
-                navigator: args.navigator,
                 data: 1,
                 child: new Text('Source'),
                 feedback: new Text('Dragging')

packages/unit/test/widget/drawer_test.dart

@@ -8,12 +8,12 @@ void main() {
 
   test('Drawer control test', () {
     testWidgets((WidgetTester tester) {
-      NavigatorState navigator;
+      BuildContext context;
       tester.pumpWidget(
         new MaterialApp(
           routes: <String, RouteBuilder>{
             '/': (RouteArguments args) {
-              navigator = args.navigator;
+              context = args.context;
               return new Container();
             }
           }
@@ -21,12 +21,12 @@ void main() {
       );
       tester.pump(); // no effect
       expect(tester.findText('drawer'), isNull);
-      showDrawer(context: navigator.context, child: new Text('drawer'));
+      showDrawer(context: context, child: new Text('drawer'));
       tester.pump(); // drawer should be starting to animate in
       expect(tester.findText('drawer'), isNotNull);
       tester.pump(new Duration(seconds: 1)); // animation done
       expect(tester.findText('drawer'), isNotNull);
-      navigator.pop();
+      Navigator.of(context).pop();
       tester.pump(); // drawer should be starting to animate away
       expect(tester.findText('drawer'), isNotNull);
       tester.pump(new Duration(seconds: 1)); // animation done
@@ -36,13 +36,13 @@ void main() {
 
   test('Drawer tap test', () {
     testWidgets((WidgetTester tester) {
-      NavigatorState navigator;
+      BuildContext context;
       tester.pumpWidget(new Container()); // throw away the old App and its Navigator
       tester.pumpWidget(
         new MaterialApp(
           routes: <String, RouteBuilder>{
             '/': (RouteArguments args) {
-              navigator = args.navigator;
+              context = args.context;
               return new Container();
             }
           }
@@ -50,7 +50,7 @@ void main() {
       );
       tester.pump(); // no effect
       expect(tester.findText('drawer'), isNull);
-      showDrawer(context: navigator.context, child: new Text('drawer'));
+      showDrawer(context: context, child: new Text('drawer'));
       tester.pump(); // drawer should be starting to animate in
       expect(tester.findText('drawer'), isNotNull);
       tester.pump(new Duration(seconds: 1)); // animation done

packages/unit/test/widget/init_state_test.dart

+// 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 'package:flutter/widgets.dart';
+import 'package:test/test.dart';
+
+import 'widget_tester.dart';
+
+List<String> ancestors = <String>[];
+
+class TestComponent extends StatefulComponent {
+  TestComponentState createState() => new TestComponentState();
+}
+
+class TestComponentState extends State<TestComponent> {
+  void initState() {
+    super.initState();
+    context.visitAncestorElements((Element element) {
+      ancestors.add(element.widget.runtimeType.toString());
+      return true;
+    });
+  }
+
+  Widget build(BuildContext context) => new Container();
+}
+
+void main() {
+  test('initState() is called when we are in the tree', () {
+    testWidgets((WidgetTester tester) {
+      tester.pumpWidget(new Container(child: new TestComponent()));
+      expect(ancestors, equals(<String>['Container', 'RenderObjectToWidgetAdapter<RenderBox>']));
+    });
+  });
+}

packages/unit/test/widget/navigator_test.dart

@@ -4,14 +4,10 @@ import 'package:test/test.dart';
 import 'widget_tester.dart';
 
 class FirstComponent extends StatelessComponent {
-  FirstComponent(this.navigator);
-
-  final NavigatorState navigator;
-
   Widget build(BuildContext context) {
     return new GestureDetector(
       onTap: () {
-        navigator.pushNamed('/second');
+        Navigator.of(context).pushNamed('/second');
       },
       child: new Container(
         decoration: new BoxDecoration(
@@ -24,17 +20,13 @@ class FirstComponent extends StatelessComponent {
 }
 
 class SecondComponent extends StatefulComponent {
-  SecondComponent(this.navigator);
-
-  final NavigatorState navigator;
-
   SecondComponentState createState() => new SecondComponentState();
 }
 
 class SecondComponentState extends State<SecondComponent> {
   Widget build(BuildContext context) {
     return new GestureDetector(
-      onTap: config.navigator.pop,
+      onTap: Navigator.of(context).pop,
       child: new Container(
         decoration: new BoxDecoration(
           backgroundColor: new Color(0xFFFF00FF)
@@ -49,8 +41,8 @@ void main() {
   test('Can navigator navigate to and from a stateful component', () {
     testWidgets((WidgetTester tester) {
       final Map<String, RouteBuilder> routes = <String, RouteBuilder>{
-        '/': (RouteArguments args) => new FirstComponent(args.navigator),
-        '/second': (RouteArguments args) => new SecondComponent(args.navigator),
+        '/': (RouteArguments args) => new FirstComponent(),
+        '/second': (RouteArguments args) => new SecondComponent(),
       };
 
       tester.pumpWidget(new Navigator(routes: routes));

packages/unit/test/widget/remember_scroll_position_test.dart

+// 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 'package:flutter/animation.dart';
+import 'package:flutter/widgets.dart';
+import 'package:test/test.dart';
+
+import 'widget_tester.dart';
+
+class ThePositiveNumbers extends ScrollableWidgetList {
+  ThePositiveNumbers() : super(itemExtent: 100.0);
+  ThePositiveNumbersState createState() => new ThePositiveNumbersState();
+}
+
+class ThePositiveNumbersState extends ScrollableWidgetListState<ThePositiveNumbers> {
+
+  ScrollBehavior createScrollBehavior() => new UnboundedBehavior();
+
+  int get itemCount => null;
+
+  List<Widget> buildItems(BuildContext context, int start, int count) {
+    List<Widget> result = new List<Widget>();
+    for (int index = start; index < start + count; index += 1)
+      result.add(new Text('$index', key: new ValueKey<int>(index)));
+    return result;
+  }
+}
+
+
+void main() {
+  test('whether we remember our scroll position', () {
+    testWidgets((WidgetTester tester) {
+      GlobalKey<NavigatorState> navigatorKey = new GlobalKey<NavigatorState>();
+      tester.pumpWidget(new Navigator(
+        key: navigatorKey,
+        routes: <String, RouteBuilder>{
+         '/': (RouteArguments args) => new Container(child: new ThePositiveNumbers()),
+         '/second': (RouteArguments args) => new Container(child: new ThePositiveNumbers()),
+        }
+      ));
+
+      // we're 600 pixels high, each item is 100 pixels high, scroll position is
+      // zero, so we should have exactly 6 items, 0..5.
+      expect(tester.findText('0'), isNotNull);
+      expect(tester.findText('1'), isNotNull);
+      expect(tester.findText('2'), isNotNull);
+      expect(tester.findText('3'), isNotNull);
+      expect(tester.findText('4'), isNotNull);
+      expect(tester.findText('5'), isNotNull);
+      expect(tester.findText('6'), isNull);
+      expect(tester.findText('10'), isNull);
+      expect(tester.findText('100'), isNull);
+
+      StatefulComponentElement<ThePositiveNumbers, ThePositiveNumbersState> target =
+        tester.findElement((Element element) => element.widget is ThePositiveNumbers);
+      target.state.scrollTo(1000.0);
+      tester.pump(new Duration(seconds: 1));
+
+      // we're 600 pixels high, each item is 100 pixels high, scroll position is
+      // 1000, so we should have exactly 6 items, 10..15.
+
+      expect(tester.findText('0'), isNull);
+      expect(tester.findText('8'), isNull);
+      expect(tester.findText('9'), isNull);
+      expect(tester.findText('10'), isNotNull);
+      expect(tester.findText('11'), isNotNull);
+      expect(tester.findText('12'), isNotNull);
+      expect(tester.findText('13'), isNotNull);
+      expect(tester.findText('14'), isNotNull);
+      expect(tester.findText('15'), isNotNull);
+      expect(tester.findText('16'), isNull);
+      expect(tester.findText('100'), isNull);
+
+      navigatorKey.currentState.pushNamed('/second');
+      tester.pump(); // navigating always takes two frames
+      tester.pump(new Duration(seconds: 1));
+
+      // same as the first list again
+      expect(tester.findText('0'), isNotNull);
+      expect(tester.findText('1'), isNotNull);
+      expect(tester.findText('2'), isNotNull);
+      expect(tester.findText('3'), isNotNull);
+      expect(tester.findText('4'), isNotNull);
+      expect(tester.findText('5'), isNotNull);
+      expect(tester.findText('6'), isNull);
+      expect(tester.findText('10'), isNull);
+      expect(tester.findText('100'), isNull);
+
+      navigatorKey.currentState.pop();
+      tester.pump(); // navigating always takes two frames
+      tester.pump(new Duration(seconds: 1));
+
+      // we're 600 pixels high, each item is 100 pixels high, scroll position is
+      // 1000, so we should have exactly 6 items, 10..15.
+
+      expect(tester.findText('0'), isNull);
+      expect(tester.findText('8'), isNull);
+      expect(tester.findText('9'), isNull);
+      expect(tester.findText('10'), isNotNull);
+      expect(tester.findText('11'), isNotNull);
+      expect(tester.findText('12'), isNotNull);
+      expect(tester.findText('13'), isNotNull);
+      expect(tester.findText('14'), isNotNull);
+      expect(tester.findText('15'), isNotNull);
+      expect(tester.findText('16'), isNull);
+      expect(tester.findText('100'), isNull);
+      
+    });
+  });
+}

packages/unit/test/widget/snack_bar_test.dart

@@ -16,7 +16,7 @@ void main() {
             return new GestureDetector(
               onTap: () {
                 showSnackBar(
-                  context: args.navigator.context,
+                  context: args.context,
                   placeholderKey: placeholderKey,
                   content: new Text(helloSnackBar)
                 );