NavigatorTransaction

To make it easier to avoid pushing twice in one frame, provide a
transaction mechanism for the navigator.

examples/fitness/lib/feed.dart

@@ -60,7 +60,7 @@ class FeedFragmentState extends State<FeedFragment> {
     setState(() {
       _fitnessMode = value;
     });
-    Navigator.of(context).pop();
+    Navigator.pop(context);
   }
 
   void _showDrawer() {
@@ -91,8 +91,7 @@ class FeedFragmentState extends State<FeedFragment> {
   }
 
   void _handleShowSettings() {
-    Navigator.of(context)..pop()
-                         ..pushNamed('/settings');
+    Navigator.popAndPushNamed(context, '/settings');
   }
 
   // TODO(jackson): We should be localizing
@@ -190,7 +189,7 @@ class FeedFragmentState extends State<FeedFragment> {
   void _handleActionButtonPressed() {
     showDialog(context: context, child: new AddItemDialog()).then((routeName) {
       if (routeName != null)
-        Navigator.of(context).pushNamed(routeName);
+        Navigator.pushNamed(context, routeName);
     });
   }
 
@@ -249,13 +248,13 @@ class AddItemDialogState extends State<AddItemDialog> {
         new FlatButton(
           child: new Text('CANCEL'),
           onPressed: () {
-            Navigator.of(context).pop();
+            Navigator.pop(context);
           }
         ),
         new FlatButton(
           child: new Text('ADD'),
           onPressed: () {
-            Navigator.of(context).pop(_addItemRoute);
+            Navigator.pop(context, _addItemRoute);
           }
         ),
       ]

examples/fitness/lib/meal.dart

@@ -55,14 +55,15 @@ class MealFragmentState extends State<MealFragment> {
 
   void _handleSave() {
     config.onCreated(new Meal(when: new DateTime.now(), description: _description));
-    Navigator.of(context).pop();
+    Navigator.pop(context);
   }
 
   Widget buildToolBar() {
     return new ToolBar(
       left: new IconButton(
         icon: "navigation/close",
-        onPressed: Navigator.of(context).pop),
+        onPressed: () => Navigator.pop(context)
+      ),
       center: new Text('New Meal'),
       right: <Widget>[
         // TODO(abarth): Should this be a FlatButton?

examples/fitness/lib/measurement.dart

@@ -77,14 +77,15 @@ class MeasurementFragmentState extends State<MeasurementFragment> {
       ));
     }
     config.onCreated(new Measurement(when: _when, weight: parsedWeight));
-    Navigator.of(context).pop();
+    Navigator.pop(context);
   }
 
   Widget buildToolBar() {
     return new ToolBar(
       left: new IconButton(
         icon: "navigation/close",
-        onPressed: Navigator.of(context).pop),
+        onPressed: () => Navigator.pop(context)
+      ),
       center: new Text('New Measurement'),
       right: <Widget>[
         // TODO(abarth): Should this be a FlatButton?

examples/fitness/lib/settings.dart

@@ -28,7 +28,7 @@ class SettingsFragmentState extends State<SettingsFragment> {
     return new ToolBar(
       left: new IconButton(
         icon: "navigation/arrow_back",
-        onPressed: () => Navigator.of(context).pop()
+        onPressed: () => Navigator.pop(context)
       ),
       center: new Text('Settings')
     );
@@ -47,7 +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}")) {
-      Navigator.of(context).pop(double.parse(goalWeight.replaceAll("\u{0}", "")));
+      Navigator.pop(context, double.parse(goalWeight.replaceAll("\u{0}", "")));
     } else {
       setState(() {
         try {
@@ -74,13 +74,13 @@ class SettingsFragmentState extends State<SettingsFragment> {
           new FlatButton(
             child: new Text('CANCEL'),
             onPressed: () {
-              Navigator.of(context).pop();
+              Navigator.pop(context);
             }
           ),
           new FlatButton(
             child: new Text('SAVE'),
             onPressed: () {
-              Navigator.of(context).pop(_goalWeight);
+              Navigator.pop(context, _goalWeight);
             }
           ),
         ]

examples/material_gallery/lib/gallery_page.dart

@@ -21,7 +21,7 @@ class GalleryPage extends StatelessComponent {
     for (WidgetDemo demo in demos) {
       items.add(new DrawerItem(
         onPressed: () {
-          Navigator.of(context).pushNamed(demo.routeName);
+          Navigator.pushNamed(context, demo.routeName);
         },
         child: new Text(demo.title)
       ));

examples/stocks/lib/stock_home.dart

@@ -41,7 +41,7 @@ class StockHomeState extends State<StockHome> {
   }
 
   void _handleSearchEnd() {
-    Navigator.of(context).pop();
+    Navigator.pop(context);
   }
 
   void _handleSearchQueryChanged(String query) {
@@ -92,13 +92,13 @@ class StockHomeState extends State<StockHome> {
                   new FlatButton(
                     child: new Text('USE IT'),
                     onPressed: () {
-                      Navigator.of(context).pop(false);
+                      Navigator.pop(context, false);
                     }
                   ),
                   new FlatButton(
                     child: new Text('OH WELL'),
                     onPressed: () {
-                      Navigator.of(context).pop(false);
+                      Navigator.pop(context, false);
                     }
                   ),
                 ]
@@ -142,8 +142,7 @@ class StockHomeState extends State<StockHome> {
   }
 
   void _handleShowSettings() {
-    Navigator.of(context)..pop()
-                         ..pushNamed('/settings');
+    Navigator.popAndPushNamed(context, '/settings');
   }
 
   Widget buildToolBar() {
@@ -207,7 +206,7 @@ class StockHomeState extends State<StockHome> {
       onOpen: (Stock stock, Key arrowKey) {
         Set<Key> mostValuableKeys = new Set<Key>();
         mostValuableKeys.add(arrowKey);
-        Navigator.of(context).pushNamed('/stock/${stock.symbol}', mostValuableKeys: mostValuableKeys);
+        Navigator.pushNamed(context, '/stock/${stock.symbol}', mostValuableKeys: mostValuableKeys);
       },
       onShow: (Stock stock, Key arrowKey) {
         scaffoldKey.currentState.showBottomSheet((BuildContext context) => new StockSymbolBottomSheet(stock: stock));

examples/stocks/lib/stock_menu.dart

@@ -23,10 +23,9 @@ Future showStockMenu({BuildContext context, bool autorefresh, ValueChanged<bool>
             new Checkbox(
               value: autorefresh,
               onChanged: (bool value) {
-                Navigator.of(context).setState(() {
-                  autorefresh = value;
-                });
-                Navigator.of(context).pop(_MenuItems.autorefreshCheckbox);
+                // TODO(ianh): https://github.com/flutter/flutter/issues/187
+                autorefresh = value;
+                Navigator.pop(context, _MenuItems.autorefreshCheckbox);
               }
             )
           ]
@@ -43,9 +42,8 @@ Future showStockMenu({BuildContext context, bool autorefresh, ValueChanged<bool>
     ]
   )) {
     case _MenuItems.autorefresh:
-      Navigator.of(context).setState(() {
-        autorefresh = !autorefresh;
-      });
+      // TODO(ianh): https://github.com/flutter/flutter/issues/187
+      autorefresh = !autorefresh;
       continue autorefreshNotify;
     autorefreshNotify:
     case _MenuItems.autorefreshCheckbox:
@@ -75,7 +73,7 @@ Future showStockMenu({BuildContext context, bool autorefresh, ValueChanged<bool>
             new FlatButton(
               child: new Text('OH WELL'),
               onPressed: () {
-                Navigator.of(context).pop(false);
+                Navigator.pop(context, false);
               }
             ),
           ]

examples/stocks/lib/stock_settings.dart

@@ -44,13 +44,13 @@ class StockSettingsState extends State<StockSettings> {
               new FlatButton(
                 child: new Text('NO THANKS'),
                 onPressed: () {
-                  Navigator.of(context).pop(false);
+                  Navigator.pop(context, false);
                 }
               ),
               new FlatButton(
                 child: new Text('AGREE'),
                 onPressed: () {
-                  Navigator.of(context).pop(true);
+                  Navigator.pop(context, true);
                 }
               ),
             ]
@@ -72,7 +72,7 @@ class StockSettingsState extends State<StockSettings> {
     return new ToolBar(
       left: new IconButton(
         icon: 'navigation/arrow_back',
-        onPressed: () => Navigator.of(context).pop()
+        onPressed: () => Navigator.pop(context)
       ),
       center: new Text('Settings')
     );

examples/stocks/lib/stock_symbol_viewer.dart

@@ -58,7 +58,7 @@ class StockSymbolPage extends StatelessComponent {
         left: new IconButton(
           icon: 'navigation/arrow_back',
           onPressed: () {
-            Navigator.of(context).pop();
+            Navigator.pop(context);
           }
         ),
         center: new Text(stock.name)

examples/widgets/navigation.dart

@@ -15,11 +15,11 @@ class Home extends StatelessComponent {
             ),
             new RaisedButton(
               child: new Text('GO SHOPPING'),
-              onPressed: () => Navigator.of(context).pushNamed('/shopping')
+              onPressed: () => Navigator.pushNamed(context, '/shopping')
             ),
             new RaisedButton(
               child: new Text('START ADVENTURE'),
-              onPressed: () => Navigator.of(context).pushNamed('/adventure')
+              onPressed: () => Navigator.pushNamed(context, '/adventure')
             )
           ],
           padding: const EdgeDims.all(30.0)
@@ -41,11 +41,11 @@ class Shopping extends StatelessComponent {
             ),
             new RaisedButton(
               child: new Text('RETURN HOME'),
-              onPressed: () => Navigator.of(context).pop()
+              onPressed: () => Navigator.pop(context)
             ),
             new RaisedButton(
               child: new Text('GO TO DUNGEON'),
-              onPressed: () => Navigator.of(context).pushNamed('/adventure')
+              onPressed: () => Navigator.pushNamed(context, '/adventure')
             )
           ],
           padding: const EdgeDims.all(30.0)
@@ -67,7 +67,7 @@ class Adventure extends StatelessComponent {
             ),
             new RaisedButton(
               child: new Text('RUN!!!'),
-              onPressed: () => Navigator.of(context).pop()
+              onPressed: () => Navigator.pop(context)
             )
           ],
           padding: const EdgeDims.all(30.0)

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

@@ -119,7 +119,7 @@ class _ModalBottomSheetState extends State<_ModalBottomSheet> {
 
   Widget build(BuildContext context) {
     return new GestureDetector(
-      onTap: () { Navigator.of(context).pop(); },
+      onTap: () => Navigator.pop(context),
       child: new BuilderTransition(
         performance: config.route.performance,
         variables: <AnimatedValue<double>>[_layout.childTop],
@@ -130,7 +130,7 @@ class _ModalBottomSheetState extends State<_ModalBottomSheet> {
               token: _layout.childTop.value,
               child: new BottomSheet(
                 performance: config.route.performance,
-                onClosing: () { Navigator.of(context).pop(); },
+                onClosing: () => Navigator.pop(context),
                 childHeight: _layout.childTop.end,
                 builder: config.route.builder
               )
@@ -167,7 +167,7 @@ Future showModalBottomSheet({ BuildContext context, WidgetBuilder builder }) {
   assert(context != null);
   assert(builder != null);
   final Completer completer = new Completer();
-  Navigator.of(context).push(new _ModalBottomSheetRoute(
+  Navigator.push(context, new _ModalBottomSheetRoute(
     completer: completer,
     builder: builder
   ));

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

@@ -40,11 +40,11 @@ class _DatePickerDialogState extends State<_DatePickerDialog> {
   }
 
   void _handleCancel() {
-    Navigator.of(context).pop();
+    Navigator.pop(context);
   }
 
   void _handleOk() {
-    Navigator.of(context).pop(_selectedDate);
+    Navigator.pop(context, _selectedDate);
   }
 
   Widget build(BuildContext context) {

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

@@ -140,6 +140,6 @@ class _DialogRoute<T> extends PopupRoute<T> {
 
 Future showDialog({ BuildContext context, Widget child }) {
   Completer completer = new Completer();
-  Navigator.of(context).push(new _DialogRoute(completer: completer, child: child));
+  Navigator.push(context, new _DialogRoute(completer: completer, child: child));
   return completer.future;
 }

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

@@ -71,7 +71,7 @@ class _DrawerRoute extends OverlayRoute {
           _state = _DrawerState.closed;
           switch (previousState) {
             case _DrawerState.showing:
-              Navigator.of(context).pop();
+              Navigator.pop(context);
               break;
             case _DrawerState.popped:
               finished();
@@ -220,5 +220,5 @@ class _DrawerControllerState extends State<_DrawerController> {
 }
 
 void showDrawer({ BuildContext context, Widget child, int elevation: 16 }) {
-  Navigator.of(context).push(new _DrawerRoute(child: child, elevation: elevation));
+  Navigator.push(context, new _DrawerRoute(child: child, elevation: elevation));
 }

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

@@ -93,9 +93,7 @@ class _DropDownMenu<T> extends StatusTransitionComponent {
             padding: _kMenuHorizontalPadding,
             child: route.items[itemIndex]
           ),
-          onTap: () {
-            Navigator.of(context).pop(route.items[itemIndex].value);
-          }
+          onTap: () => Navigator.pop(context, route.items[itemIndex].value)
         )
       ));
     }
@@ -117,7 +115,7 @@ class _DropDownMenu<T> extends StatusTransitionComponent {
       reverseCurve: const Interval(0.0, 0.001)
     );
 
-    final RenderBox renderBox = Navigator.of(context).context.findRenderObject();
+    final RenderBox renderBox = route.navigator.context.findRenderObject();
     final Size navigatorSize = renderBox.size;
     final RelativeRect menuRect = new RelativeRect.fromSize(route.rect, navigatorSize);
 
@@ -216,7 +214,7 @@ class DropDownButton<T> extends StatelessComponent {
     final RenderBox renderBox = indexedStackKey.currentContext.findRenderObject();
     final Rect rect = renderBox.localToGlobal(Point.origin) & renderBox.size;
     final Completer completer = new Completer<T>();
-    Navigator.of(context).push(new _DropDownRoute<T>(
+    Navigator.push(context, new _DropDownRoute<T>(
       completer: completer,
       items: items,
       selectedIndex: selectedIndex,

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

@@ -81,8 +81,10 @@ class _MaterialAppState extends State<MaterialApp> implements BindingObserver {
     assert(mounted);
     NavigatorState navigator = _navigator.currentState;
     assert(navigator != null);
-    if (!navigator.pop())
-      activity.finishCurrentActivity();
+    navigator.openTransaction((NavigatorTransaction transaction) {
+      if (!transaction.pop())
+        activity.finishCurrentActivity();
+    });
     return true;
   }
 

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

@@ -38,7 +38,7 @@ class _PopupMenu<T> extends StatelessComponent {
         performance: route.performance,
         opacity: new AnimatedValue<double>(0.0, end: 1.0, curve: new Interval(start, end)),
         child: new InkWell(
-          onTap: () { Navigator.of(context).pop(route.items[i].value); },
+          onTap: () => Navigator.pop(context, route.items[i].value),
           child: route.items[i]
         ))
       );
@@ -114,7 +114,7 @@ class _PopupMenuRoute<T> extends PopupRoute<T> {
 
 Future showMenu({ BuildContext context, ModalPosition position, List<PopupMenuItem> items, int elevation: 8 }) {
   Completer completer = new Completer();
-  Navigator.of(context).push(new _PopupMenuRoute(
+  Navigator.push(context, new _PopupMenuRoute(
     completer: completer,
     position: position,
     items: items,

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

@@ -36,11 +36,11 @@ class _TimePickerDialogState extends State<_TimePickerDialog> {
   }
 
   void _handleCancel() {
-    Navigator.of(context).pop();
+    Navigator.pop(context);
   }
 
   void _handleOk() {
-    Navigator.of(context).pop(_selectedTime);
+    Navigator.pop(context, _selectedTime);
   }
 
   Widget build(BuildContext context) {

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

@@ -11,7 +11,6 @@ import 'package:flutter/services.dart';
 import 'basic.dart';
 import 'binding.dart';
 import 'framework.dart';
-import 'navigator.dart';
 import 'overlay.dart';
 
 typedef bool DragTargetWillAccept<T>(T data);
@@ -165,7 +164,7 @@ class _DraggableState<T> extends State<DraggableBase<T>> implements GestureArena
     new _DragAvatar<T>(
       pointer: pointer,
       router: router,
-      overlay: Navigator.of(context).overlay,
+      overlay: Overlay.of(context),
       data: config.data,
       initialPosition: position,
       dragStartPoint: dragStartPoint,

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

@@ -23,7 +23,7 @@ class ModalBarrier extends StatelessComponent {
     return new Listener(
       onPointerDown: (_) {
         if (dismissable)
-          Navigator.of(context).pop();
+          Navigator.pop(context);
       },
       behavior: HitTestBehavior.opaque,
       child: new ConstrainedBox(

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

@@ -14,13 +14,13 @@ abstract class Route<T> {
 
   /// Called when the route is inserted into the navigator.
   ///
-  /// Use this to populate overlayEntries and add them to the overlay.
-  /// (The reason the Route is responsible for doing this, rather than the
-  /// Navigator, is that the Route will be responsible for _removing_ the
-  /// entries and this way it's symmetric.
+  /// Use this to populate overlayEntries and add them to the overlay
+  /// (accessible as navigator.overlay). (The reason the Route is responsible
+  /// for doing this, rather than the Navigator, is that the Route will be
+  /// responsible for _removing_ the entries and this way it's symmetric.)
   ///
   /// The overlay argument will be null if this is the first route inserted.
-  void install(OverlayState overlay, OverlayEntry insertionPoint) { }
+  void install(OverlayEntry insertionPoint) { }
 
   /// Called after install() when the route is pushed onto the navigator.
   void didPush() { }
@@ -81,6 +81,7 @@ class NamedRouteSettings {
 }
 
 typedef Route RouteFactory(NamedRouteSettings settings);
+typedef void NavigatorTransactionCallback(NavigatorTransaction transaction);
 
 class NavigatorObserver {
   /// The navigator that the observer is observing, if any.
@@ -108,7 +109,37 @@ class Navigator extends StatefulComponent {
 
   static const String defaultRouteName = '/';
 
-  static NavigatorState of(BuildContext context) => context.ancestorStateOfType(NavigatorState);
+  static void pushNamed(BuildContext context, String routeName, { Set<Key> mostValuableKeys }) {
+    openTransaction(context, (NavigatorTransaction transaction) {
+      transaction.pushNamed(routeName, mostValuableKeys: mostValuableKeys);
+    });
+  }
+
+  static void push(BuildContext context, Route route, { Set<Key> mostValuableKeys }) {
+    openTransaction(context, (NavigatorTransaction transaction) {
+      transaction.push(route, mostValuableKeys: mostValuableKeys);
+    });
+  }
+
+  static bool pop(BuildContext context, [ dynamic result ]) {
+    bool returnValue;
+    openTransaction(context, (NavigatorTransaction transaction) {
+      returnValue = transaction.pop(result);
+    });
+    return returnValue;
+  }
+
+  static void popAndPushNamed(BuildContext context, String routeName, { Set<Key> mostValuableKeys }) {
+    openTransaction(context, (NavigatorTransaction transaction) {
+      transaction.pop();
+      transaction.pushNamed(routeName, mostValuableKeys: mostValuableKeys);
+    });
+  }
+
+  static void openTransaction(BuildContext context, NavigatorTransactionCallback callback) {
+    NavigatorState navigator = context.ancestorStateOfType(NavigatorState);
+    navigator.openTransaction(callback);
+  }
 
   NavigatorState createState() => new NavigatorState();
 }
@@ -121,7 +152,7 @@ class NavigatorState extends State<Navigator> {
     super.initState();
     assert(config.observer == null || config.observer.navigator == null);
     config.observer?._navigator = this;
-    push(config.onGenerateRoute(new NamedRouteSettings(
+    _push(config.onGenerateRoute(new NamedRouteSettings(
       name: config.initialRoute ?? Navigator.defaultRouteName
     )));
   }
@@ -146,9 +177,10 @@ class NavigatorState extends State<Navigator> {
     assert(() { _debugLocked = false; return true; });
   }
 
+  // Used by Routes and NavigatorObservers
   OverlayState get overlay => _overlayKey.currentState;
 
-  OverlayEntry get _currentOverlay {
+  OverlayEntry get _currentOverlayEntry {
     for (Route route in _history.reversed) {
       if (route.overlayEntries.isNotEmpty)
         return route.overlayEntries.last;
@@ -158,17 +190,17 @@ class NavigatorState extends State<Navigator> {
 
   bool _debugLocked = false; // used to prevent re-entrant calls to push, pop, and friends
 
-  void pushNamed(String name, { Set<Key> mostValuableKeys }) {
+  void _pushNamed(String name, { Set<Key> mostValuableKeys }) {
     assert(!_debugLocked);
     assert(name != null);
     NamedRouteSettings settings = new NamedRouteSettings(
       name: name,
       mostValuableKeys: mostValuableKeys
     );
-    push(config.onGenerateRoute(settings) ?? config.onUnknownRoute(settings));
+    _push(config.onGenerateRoute(settings) ?? config.onUnknownRoute(settings));
   }
 
-  void push(Route route, { Set<Key> mostValuableKeys }) {
+  void _push(Route route, { Set<Key> mostValuableKeys }) {
     assert(!_debugLocked);
     assert(() { _debugLocked = true; return true; });
     assert(route != null);
@@ -176,7 +208,7 @@ class NavigatorState extends State<Navigator> {
     setState(() {
       Route oldRoute = _history.isNotEmpty ? _history.last : null;
       route._navigator = this;
-      route.install(overlay, _currentOverlay);
+      route.install(_currentOverlayEntry);
       _history.add(route);
       route.didPush();
       if (oldRoute != null)
@@ -186,18 +218,7 @@ class NavigatorState extends State<Navigator> {
     assert(() { _debugLocked = false; return true; });
   }
 
-  /// Replaces one given route with another, but does not call didPush/didPop.
-  /// Instead, this calls install() on the new route, then didReplace() on the
-  /// new route passing the old route, then dispose() on the old route.
-  ///
-  /// The old route must have overlays, otherwise we won't know where to insert
-  /// the overlays of the new route. The old route must not be currently visible
-  /// (i.e. a later route have overlays that are currently opaque), otherwise
-  /// the replacement would have a jarring effect.
-  ///
-  /// It is safe to call this redundantly (replacing a route with itself). Such
-  /// calls are ignored.
-  void replace({ Route oldRoute, Route newRoute }) {
+  void _replace({ Route oldRoute, Route newRoute }) {
     assert(!_debugLocked);
     assert(oldRoute != null);
     assert(newRoute != null);
@@ -213,7 +234,7 @@ class NavigatorState extends State<Navigator> {
       int index = _history.indexOf(oldRoute);
       assert(index >= 0);
       newRoute._navigator = this;
-      newRoute.install(overlay, oldRoute.overlayEntries.last);
+      newRoute.install(oldRoute.overlayEntries.last);
       _history[index] = newRoute;
       newRoute.didReplace(oldRoute);
       if (index > 0)
@@ -224,24 +245,14 @@ class NavigatorState extends State<Navigator> {
     assert(() { _debugLocked = false; return true; });
   }
 
-  /// Like replace(), but affects the route before the given anchorRoute rather
-  /// than the anchorRoute itself.
-  ///
-  /// If newRoute is already the route before anchorRoute, then the call is
-  /// ignored.
-  ///
-  /// The conditions described for [replace()] apply; for instance, the route
-  /// before anchorRoute must have overlays.
-  void replaceRouteBefore({ Route anchorRoute, Route newRoute }) {
+  void _replaceRouteBefore({ Route anchorRoute, Route newRoute }) {
     assert(anchorRoute != null);
     assert(anchorRoute._navigator == this);
     assert(_history.indexOf(anchorRoute) > 0);
-    replace(oldRoute: _history[_history.indexOf(anchorRoute)-1], newRoute: newRoute);
+    _replace(oldRoute: _history[_history.indexOf(anchorRoute)-1], newRoute: newRoute);
   }
  
-  /// Removes the route prior to the given anchorRoute without notifying
-  /// neighbouring routes or the navigator observer, if any.
-  void removeRouteBefore(Route anchorRoute) {
+  void _removeRouteBefore(Route anchorRoute) {
     assert(!_debugLocked);
     assert(() { _debugLocked = true; return true; });
     assert(anchorRoute._navigator == this);
@@ -258,16 +269,7 @@ class NavigatorState extends State<Navigator> {
     assert(() { _debugLocked = false; return true; });
   }
 
-  /// Removes the current route, notifying the observer (if any), and the
-  /// previous routes (using [Route.didPopNext]).
-  ///
-  /// The type of the result argument, if provided, must match the type argument
-  /// of the class of the current route. (In practice, this is usually
-  /// "dynamic".)
-  ///
-  /// Returns true if a route was popped; returns false if there are no further
-  /// previous routes.
-  bool pop([dynamic result]) {
+  bool _pop([dynamic result]) {
     assert(!_debugLocked);
     assert(() { _debugLocked = true; return true; });
     Route route = _history.last;
@@ -292,20 +294,123 @@ class NavigatorState extends State<Navigator> {
     return true;
   }
 
-  /// Calls pop() repeatedly until the given route is the current route.
-  /// If it is already the current route, nothing happens.
-  void popUntil(Route targetRoute) {
+  void _popUntil(Route targetRoute) {
     assert(_history.contains(targetRoute));
     while (!targetRoute.isCurrent)
-      pop();
+      _pop();
+  }
+
+  bool _hadTransaction = true;
+
+  bool openTransaction(NavigatorTransactionCallback callback) {
+    assert(callback != null);
+    if (_hadTransaction)
+      return false;
+    _hadTransaction = true;
+    NavigatorTransaction transaction = new NavigatorTransaction._(this);
+    setState(() {
+      callback(transaction);
+    });
+    assert(() { transaction._debugClose(); return true; });
+    return true;
   }
 
   Widget build(BuildContext context) {
     assert(!_debugLocked);
     assert(_history.isNotEmpty);
+    _hadTransaction = false;
     return new Overlay(
       key: _overlayKey,
       initialEntries: _history.first.overlayEntries
     );
   }
 }
+
+class NavigatorTransaction {
+  NavigatorTransaction._(this._navigator) {
+    assert(_navigator != null);
+  }
+  NavigatorState _navigator;
+  bool _debugOpen = true;
+ 
+  /// Invokes the Navigator's onGenerateRoute callback to create a route with
+  /// the given name, then calls [push()] with that route.
+  void pushNamed(String name, { Set<Key> mostValuableKeys }) {
+    assert(_debugOpen);
+    _navigator._pushNamed(name, mostValuableKeys: mostValuableKeys);
+  }
+
+  /// Adds the given route to the Navigator's history, and transitions to it.
+  /// The route will have didPush() called on it; the previous route, if any,
+  /// will have didPushNext() called on it; and the Navigator observer, if any,
+  /// will have didPush() called on it.
+  void push(Route route, { Set<Key> mostValuableKeys }) {
+    assert(_debugOpen);
+    _navigator._push(route, mostValuableKeys: mostValuableKeys);
+  }
+
+  /// Replaces one given route with another, but does not call didPush/didPop.
+  /// Instead, this calls install() on the new route, then didReplace() on the
+  /// new route passing the old route, then dispose() on the old route. The
+  /// navigator is not informed of the replacement.
+  ///
+  /// The old route must have overlay entries, otherwise we won't know where to
+  /// insert the entries of the new route. The old route must not be currently
+  /// visible (i.e. a later route have overlay entries that are currently
+  /// opaque), otherwise the replacement would have a jarring effect.
+  ///
+  /// It is safe to call this redundantly (replacing a route with itself). Such
+  /// calls are ignored.
+  void replace({ Route oldRoute, Route newRoute }) {
+    assert(_debugOpen);
+    _navigator._replace(oldRoute: oldRoute, newRoute: newRoute);
+  }
+
+  /// Like replace(), but affects the route before the given anchorRoute rather
+  /// than the anchorRoute itself.
+  ///
+  /// If newRoute is already the route before anchorRoute, then the call is
+  /// ignored.
+  ///
+  /// The conditions described for [replace()] apply; for instance, the route
+  /// before anchorRoute must have overlay entries.
+  void replaceRouteBefore({ Route anchorRoute, Route newRoute }) {
+    assert(_debugOpen);
+    _navigator._replaceRouteBefore(anchorRoute: anchorRoute, newRoute: newRoute);
+  }
+
+  /// Removes the route prior to the given anchorRoute without notifying
+  /// neighbouring routes or the navigator observer, if any.
+  void removeRouteBefore(Route anchorRoute) {
+    assert(_debugOpen);
+    _navigator._removeRouteBefore(anchorRoute);
+  }
+
+  /// Tries to removes the current route, calling its didPop() method. If that
+  /// method returns false, then nothing else happens. Otherwise, the observer
+  /// (if any) is notified using its didPop() method, and the previous route is
+  /// notified using [Route.didPopNext].
+  ///
+  /// The type of the result argument, if provided, must match the type argument
+  /// of the class of the current route. (In practice, this is usually
+  /// "dynamic".)
+  ///
+  /// Returns true if a route was popped; returns false if there are no further
+  /// previous routes.
+  bool pop([dynamic result]) {
+    assert(_debugOpen);
+    return _navigator._pop(result);
+  }
+ 
+  /// Calls pop() repeatedly until the given route is the current route.
+  /// If it is already the current route, nothing happens.
+  void popUntil(Route targetRoute) {
+    assert(_debugOpen);
+    _navigator._popUntil(targetRoute);
+  }
+
+  void _debugClose() {
+    assert(_debugOpen);
+    _debugOpen = false;
+  }
+}
\ No newline at end of file

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

@@ -44,6 +44,8 @@ class Overlay extends StatefulComponent {
 
   final List<OverlayEntry> initialEntries;
 
+  static OverlayState of(BuildContext context) => context.ancestorStateOfType(OverlayState);
+
   OverlayState createState() => new OverlayState();
 }
 

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

@@ -23,11 +23,11 @@ abstract class OverlayRoute<T> extends Route<T> {
   List<OverlayEntry> get overlayEntries => _overlayEntries;
   final List<OverlayEntry> _overlayEntries = <OverlayEntry>[];
 
-  void install(OverlayState overlay, OverlayEntry insertionPoint) {
+  void install(OverlayEntry insertionPoint) {
     assert(_overlayEntries.isEmpty);
     for (WidgetBuilder builder in builders)
       _overlayEntries.add(new OverlayEntry(builder: builder));
-    overlay?.insertAll(_overlayEntries, above: insertionPoint);
+    navigator.overlay?.insertAll(_overlayEntries, above: insertionPoint);
   }
 
   // Subclasses shouldn't call this if they want to delay the finished() call.
@@ -108,9 +108,9 @@ abstract class TransitionRoute<T> extends OverlayRoute<T> {
     }
   }
 
-  void install(OverlayState overlay, OverlayEntry insertionPoint) {
+  void install(OverlayEntry insertionPoint) {
     _performance = createPerformance();
-    super.install(overlay, insertionPoint);
+    super.install(insertionPoint);
   }
 
   void didPush() {

packages/unit/test/widget/drawer_test.dart

@@ -29,7 +29,7 @@ void main() {
       expect(tester.findText('drawer'), isNotNull);
       tester.pump(new Duration(seconds: 1)); // animation done
       expect(tester.findText('drawer'), isNotNull);
-      Navigator.of(context).pop();
+      Navigator.pop(context);
       tester.pump(); // drawer should be starting to animate away
       expect(tester.findText('drawer'), isNotNull);
       tester.pump(new Duration(seconds: 1)); // animation done

packages/unit/test/widget/heroes_test.dart

@@ -15,13 +15,13 @@ final Map<String, RouteBuilder> routes = <String, RouteBuilder>{
     new Container(height: 100.0, width: 100.0),
     new Card(child: new Hero(tag: 'a', child: new Container(height: 100.0, width: 100.0, key: firstKey))),
     new Container(height: 100.0, width: 100.0),
-    new FlatButton(child: new Text('button'), onPressed: () => Navigator.of(args.context).pushNamed('/two')),
+    new FlatButton(child: new Text('button'), onPressed: () => Navigator.pushNamed(args.context, '/two')),
   ]),
   '/two': (RouteArguments args) => new Block([
     new Container(height: 150.0, width: 150.0),
     new Card(child: new Hero(tag: 'a', child: new Container(height: 150.0, width: 150.0, key: secondKey))),
     new Container(height: 150.0, width: 150.0),
-    new FlatButton(child: new Text('button'), onPressed: () => Navigator.of(args.context).pop()),
+    new FlatButton(child: new Text('button'), onPressed: () => Navigator.pop(args.context)),
   ]),
 };
 

packages/unit/test/widget/navigator_test.dart

@@ -10,7 +10,7 @@ class FirstComponent extends StatelessComponent {
   Widget build(BuildContext context) {
     return new GestureDetector(
       onTap: () {
-        Navigator.of(context).pushNamed('/second');
+        Navigator.pushNamed(context, '/second');
       },
       child: new Container(
         decoration: new BoxDecoration(
@@ -29,7 +29,7 @@ class SecondComponent extends StatefulComponent {
 class SecondComponentState extends State<SecondComponent> {
   Widget build(BuildContext context) {
     return new GestureDetector(
-      onTap: Navigator.of(context).pop,
+      onTap: () => Navigator.pop(context),
       child: new Container(
         decoration: new BoxDecoration(
           backgroundColor: new Color(0xFFFF00FF)

packages/unit/test/widget/page_transitions_test.dart

@@ -16,10 +16,11 @@ class TestOverlayRoute extends OverlayRoute {
 void main() {
   test('Check onstage/offstage handling around transitions', () {
     testWidgets((WidgetTester tester) {
-      GlobalKey containerKey = new GlobalKey();
+      GlobalKey containerKey1 = new GlobalKey();
+      GlobalKey containerKey2 = new GlobalKey();
       final Map<String, RouteBuilder> routes = <String, RouteBuilder>{
-        '/': (_) => new Container(key: containerKey, child: new Text('Home')),
-        '/settings': (_) => new Container(child: new Text('Settings')),
+        '/': (_) => new Container(key: containerKey1, child: new Text('Home')),
+        '/settings': (_) => new Container(key: containerKey2, child: new Text('Settings')),
       };
 
       tester.pumpWidget(new MaterialApp(routes: routes));
@@ -28,9 +29,7 @@ void main() {
       expect(tester.findText('Settings'), isNull);
       expect(tester.findText('Overlay'), isNull);
 
-      NavigatorState navigator = Navigator.of(containerKey.currentContext);
-
-      navigator.pushNamed('/settings');
+      Navigator.pushNamed(containerKey1.currentContext, '/settings');
 
       tester.pump();
 
@@ -50,7 +49,7 @@ void main() {
       expect(tester.findText('Settings'), isOnStage);
       expect(tester.findText('Overlay'), isNull);
 
-      navigator.push(new TestOverlayRoute());
+      Navigator.push(containerKey2.currentContext, new TestOverlayRoute());
 
       tester.pump();
 
@@ -64,7 +63,7 @@ void main() {
       expect(tester.findText('Settings'), isOnStage);
       expect(tester.findText('Overlay'), isOnStage);
 
-      navigator.pop();
+      Navigator.pop(containerKey2.currentContext);
       tester.pump();
 
       expect(tester.findText('Home'), isNull);
@@ -77,7 +76,7 @@ void main() {
       expect(tester.findText('Settings'), isOnStage);
       expect(tester.findText('Overlay'), isNull);
 
-      navigator.pop();
+      Navigator.pop(containerKey2.currentContext);
       tester.pump();
 
       expect(tester.findText('Home'), isOnStage);

packages/unit/test/widget/remember_scroll_position_test.dart

@@ -74,7 +74,9 @@ void main() {
       expect(tester.findText('16'), isNull);
       expect(tester.findText('100'), isNull);
 
-      navigatorKey.currentState.pushNamed('/second');
+      navigatorKey.currentState.openTransaction(
+        (NavigatorTransaction transaction) => transaction.pushNamed('/second')
+      );
       tester.pump(); // navigating always takes two frames
       tester.pump(new Duration(seconds: 1));
 
@@ -89,7 +91,9 @@ void main() {
       expect(tester.findText('10'), isNull);
       expect(tester.findText('100'), isNull);
 
-      navigatorKey.currentState.pop();
+      navigatorKey.currentState.openTransaction(
+        (NavigatorTransaction transaction) => transaction.pop()
+      );
       tester.pump(); // navigating always takes two frames
       tester.pump(new Duration(seconds: 1));
 

packages/unit/test/widget/routes_test.dart

@@ -22,14 +22,14 @@ class TestRoute extends Route<String> {
     results.add('$name: $s');
   }
 
-  void install(OverlayState overlay, OverlayEntry insertionPoint) {
+  void install(OverlayEntry insertionPoint) {
     log('install');
     OverlayEntry entry = new OverlayEntry(
       builder: (BuildContext context) => new Container(),
       opaque: true
     );
     _entries.add(entry);
-    overlay?.insert(entry, above: insertionPoint);
+    navigator.overlay?.insert(entry, above: insertionPoint);
     routes.add(this);
   }
 
@@ -73,11 +73,11 @@ class TestRoute extends Route<String> {
 void runNavigatorTest(
   WidgetTester tester,
   NavigatorState host,
-  void test(NavigatorState transaction),
+  NavigatorTransactionCallback test,
   List<String> expectations
 ) {
   expect(host, isNotNull);
-  test(host);
+  host.openTransaction(test);
   expect(results, equals(expectations));
   results.clear();
   tester.pump();
@@ -95,7 +95,7 @@ void main() {
       runNavigatorTest(
         tester,
         host,
-        (NavigatorState transaction) {
+        (NavigatorTransaction transaction) {
         },
         [
           'initial: install',
@@ -106,7 +106,7 @@ void main() {
       runNavigatorTest(
         tester,
         host,
-        (NavigatorState transaction) {
+        (NavigatorTransaction transaction) {
           transaction.push(second = new TestRoute('second'));
         },
         [
@@ -118,7 +118,7 @@ void main() {
       runNavigatorTest(
         tester,
         host,
-        (NavigatorState transaction) {
+        (NavigatorTransaction transaction) {
           transaction.push(new TestRoute('third'));
         },
         [
@@ -130,7 +130,7 @@ void main() {
       runNavigatorTest(
         tester,
         host,
-        (NavigatorState transaction) {
+        (NavigatorTransaction transaction) {
           transaction.replace(oldRoute: second, newRoute: new TestRoute('two'));
         },
         [
@@ -143,7 +143,7 @@ void main() {
       runNavigatorTest(
         tester,
         host,
-        (NavigatorState transaction) {
+        (NavigatorTransaction transaction) {
           transaction.pop('hello');
         },
         [
@@ -155,7 +155,7 @@ void main() {
       runNavigatorTest(
         tester,
         host,
-        (NavigatorState transaction) {
+        (NavigatorTransaction transaction) {
           transaction.pop('good bye');
         },
         [
@@ -182,7 +182,7 @@ void main() {
       runNavigatorTest(
         tester,
         host,
-        (NavigatorState transaction) {
+        (NavigatorTransaction transaction) {
         },
         [
           'first: install',
@@ -193,7 +193,7 @@ void main() {
       runNavigatorTest(
         tester,
         host,
-        (NavigatorState transaction) {
+        (NavigatorTransaction transaction) {
           transaction.push(second = new TestRoute('second'));
         },
         [
@@ -205,7 +205,7 @@ void main() {
       runNavigatorTest(
         tester,
         host,
-        (NavigatorState transaction) {
+        (NavigatorTransaction transaction) {
           transaction.push(new TestRoute('third'));
         },
         [
@@ -217,7 +217,7 @@ void main() {
       runNavigatorTest(
         tester,
         host,
-        (NavigatorState transaction) {
+        (NavigatorTransaction transaction) {
           transaction.removeRouteBefore(second);
         },
         [
@@ -227,7 +227,7 @@ void main() {
       runNavigatorTest(
         tester,
         host,
-        (NavigatorState transaction) {
+        (NavigatorTransaction transaction) {
           transaction.pop('good bye');
         },
         [
@@ -239,7 +239,7 @@ void main() {
       runNavigatorTest(
         tester,
         host,
-        (NavigatorState transaction) {
+        (NavigatorTransaction transaction) {
           transaction.push(new TestRoute('three'));
         },
         [
@@ -252,7 +252,7 @@ void main() {
       runNavigatorTest(
         tester,
         host,
-        (NavigatorState transaction) {
+        (NavigatorTransaction transaction) {
           transaction.push(four = new TestRoute('four'));
         },
         [
@@ -264,7 +264,7 @@ void main() {
       runNavigatorTest(
         tester,
         host,
-        (NavigatorState transaction) {
+        (NavigatorTransaction transaction) {
           transaction.removeRouteBefore(four);
         },
         [
@@ -274,7 +274,7 @@ void main() {
       runNavigatorTest(
         tester,
         host,
-        (NavigatorState transaction) {
+        (NavigatorTransaction transaction) {
           transaction.pop('the end');
         },
         [
@@ -301,7 +301,7 @@ void main() {
       runNavigatorTest(
         tester,
         host,
-        (NavigatorState transaction) {
+        (NavigatorTransaction transaction) {
         },
         [
           'A: install',
@@ -311,7 +311,7 @@ void main() {
       runNavigatorTest(
         tester,
         host,
-        (NavigatorState transaction) {
+        (NavigatorTransaction transaction) {
           transaction.push(new TestRoute('B'));
         },
         [
@@ -324,7 +324,7 @@ void main() {
       runNavigatorTest(
         tester,
         host,
-        (NavigatorState transaction) {
+        (NavigatorTransaction transaction) {
           transaction.push(routeC = new TestRoute('C'));
         },
         [
@@ -337,7 +337,7 @@ void main() {
       runNavigatorTest(
         tester,
         host,
-        (NavigatorState transaction) {
+        (NavigatorTransaction transaction) {
           transaction.replaceRouteBefore(anchorRoute: routeC, newRoute: routeB = new TestRoute('b'));
         },
         [
@@ -350,7 +350,7 @@ void main() {
       runNavigatorTest(
         tester,
         host,
-        (NavigatorState transaction) {
+        (NavigatorTransaction transaction) {
           transaction.popUntil(routeB);
         },
         [