Port AppBar to Scrollable2 (#7996)

Move the back button and drawer opening logic into the app bar.

Move the tap-status-bar-to-scroll-to-top logic to using
ScrollControllers. Provide a PrimaryScrollController and a `primary`
flag on scroll views.

Make it possible to track when a route becomes or stops being poppable.

examples/flutter_gallery/lib/demo/pesto_demo.dart

@@ -86,24 +86,27 @@ class _RecipeGridPageState extends State<RecipeGridPage> {
       data: _kTheme.copyWith(platform: Theme.of(context).platform),
       child: new Scaffold(
         key: scaffoldKey,
-        scrollableKey: config.scrollableKey,
-        appBarBehavior: AppBarBehavior.under,
-        appBar: _buildAppBar(context, statusBarHeight),
         floatingActionButton: new FloatingActionButton(
           child: new Icon(Icons.edit),
           onPressed: () {
             scaffoldKey.currentState.showSnackBar(new SnackBar(
-              content: new Text('Not supported.')
+              content: new Text('Not supported.'),
             ));
           },
         ),
-        body: _buildBody(context, statusBarHeight),
+        body: new CustomScrollView(
+          slivers: <Widget>[
+            _buildAppBar(context, statusBarHeight),
+            _buildBody(context, statusBarHeight),
+          ],
+        ),
       )
     );
   }
 
   Widget _buildAppBar(BuildContext context, double statusBarHeight) {
-    return new AppBar(
+    return new SliverAppBar(
+      pinned: true,
       expandedHeight: _kAppBarHeight,
       actions: <Widget>[
         new IconButton(
@@ -111,7 +114,7 @@ class _RecipeGridPageState extends State<RecipeGridPage> {
           tooltip: 'Search',
           onPressed: () {
             scaffoldKey.currentState.showSnackBar(new SnackBar(
-              content: new Text('Not supported.')
+              content: new Text('Not supported.'),
             ));
           },
         ),
@@ -138,22 +141,25 @@ class _RecipeGridPageState extends State<RecipeGridPage> {
   }
 
   Widget _buildBody(BuildContext context, double statusBarHeight) {
-    final EdgeInsets padding = new EdgeInsets.fromLTRB(8.0, 8.0 + _kAppBarHeight + statusBarHeight, 8.0, 8.0);
-
-    return new ScrollableGrid(
-      scrollableKey: config.scrollableKey,
-      delegate: new MaxTileWidthGridDelegate(
-        maxTileWidth: _kRecipePageMaxWidth,
-        rowSpacing: 8.0,
-        columnSpacing: 8.0,
-        padding: padding
+    final EdgeInsets padding = const EdgeInsets.all(8.0);
+    return new SliverPadding(
+      padding: padding,
+      child: new SliverGrid(
+        gridDelegate: new SliverGridDelegateWithMaxCrossAxisExtent(
+          maxCrossAxisExtent: _kRecipePageMaxWidth,
+          crossAxisSpacing: 8.0,
+          mainAxisSpacing: 8.0,
+        ),
+        delegate: new SliverChildBuilderDelegate(
+          (BuildContext context, int index) {
+            Recipe recipe = config.recipes[index];
+            return new RecipeCard(
+              recipe: recipe,
+              onTap: () { showRecipePage(context, recipe); },
+            );
+          }
+        ),
       ),
-      children: config.recipes.map((Recipe recipe) {
-        return new RecipeCard(
-          recipe: recipe,
-          onTap: () { showRecipePage(context, recipe); }
-        );
-      }),
     );
   }
 
@@ -297,84 +303,69 @@ class RecipePage extends StatefulWidget {
 
 class _RecipePageState extends State<RecipePage> {
   final GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState>();
-  final GlobalKey<ScrollableState> _scrollableKey = new GlobalKey<ScrollableState>();
   final TextStyle menuItemStyle = new PestoStyle(fontSize: 15.0, color: Colors.black54, height: 24.0/15.0);
-  final Object _disableHeroTransition = new Object();
 
   double _getAppBarHeight(BuildContext context) => MediaQuery.of(context).size.height * 0.3;
 
   @override
   Widget build(BuildContext context) {
-    return new Scaffold(
-      key: _scaffoldKey,
-      scrollableKey: _scrollableKey,
-      appBarBehavior: AppBarBehavior.scroll,
-      appBar: new AppBar(
-        heroTag: _disableHeroTransition,
-        expandedHeight: _getAppBarHeight(context) - _kFabHalfSize,
-        backgroundColor: Colors.transparent,
-        elevation: 0,
-        actions: <Widget>[
-          new PopupMenuButton<String>(
-            onSelected: (String item) {},
-            itemBuilder: (BuildContext context) => <PopupMenuItem<String>>[
-              _buildMenuItem(Icons.share, 'Tweet recipe'),
-              _buildMenuItem(Icons.email, 'Email recipe'),
-              _buildMenuItem(Icons.message, 'Message recipe'),
-              _buildMenuItem(Icons.people, 'Share on Facebook'),
-            ]
-          )
-        ],
-        flexibleSpace: new FlexibleSpaceBar(
-          background: new DecoratedBox(
-            decoration: new BoxDecoration(
-              gradient: new LinearGradient(
-                begin: const FractionalOffset(0.5, 0.0),
-                end: const FractionalOffset(0.5, 0.40),
-                colors: <Color>[const Color(0x60000000), const Color(0x00000000)],
-              )
-            )
-          )
-        ),
-      ),
-      body: _buildBody(context),
-    );
-  }
-
-  // The full page content with the recipe's image behind it. This
-  // adjusts based on the size of the screen. If the recipe sheet touches
-  // the edge of the screen, use a slightly different layout.
-  Widget _buildBody(BuildContext context) {
-    final bool isFavorite = _favoriteRecipes.contains(config.recipe);
+    // The full page content with the recipe's image behind it. This
+    // adjusts based on the size of the screen. If the recipe sheet touches
+    // the edge of the screen, use a slightly different layout.
+    final double appBarHeight = _getAppBarHeight(context);
     final Size screenSize = MediaQuery.of(context).size;
     final bool fullWidth = (screenSize.width < _kRecipePageMaxWidth);
-    final double appBarHeight = _getAppBarHeight(context);
-    return new Stack(
-      children: <Widget>[
-        new Positioned(
-          top: 0.0,
-          left: 0.0,
-          right: 0.0,
-          height: appBarHeight + _kFabHalfSize,
-          child: new Hero(
-            tag: config.recipe.imagePath,
-            child: new Image.asset(
-              config.recipe.imagePath,
-              fit: fullWidth ? ImageFit.fitWidth : ImageFit.cover,
+    final bool isFavorite = _favoriteRecipes.contains(config.recipe);
+    return new Scaffold(
+      key: _scaffoldKey,
+      body: new Stack(
+        children: <Widget>[
+          new Positioned(
+            top: 0.0,
+            left: 0.0,
+            right: 0.0,
+            height: appBarHeight + _kFabHalfSize,
+            child: new Hero(
+              tag: config.recipe.imagePath,
+              child: new Image.asset(
+                config.recipe.imagePath,
+                fit: fullWidth ? ImageFit.fitWidth : ImageFit.cover,
+              ),
             ),
           ),
-        ),
-        new ClampOverscrolls(
-          edge: ScrollableEdge.both,
-          child: new ScrollableViewport(
-            scrollableKey: _scrollableKey,
-            child: new RepaintBoundary(
-              child: new Padding(
-                padding: new EdgeInsets.only(top: appBarHeight),
+          new CustomScrollView(
+            slivers: <Widget>[
+              new SliverAppBar(
+                expandedHeight: appBarHeight - _kFabHalfSize,
+                backgroundColor: Colors.transparent,
+                actions: <Widget>[
+                  new PopupMenuButton<String>(
+                    onSelected: (String item) {},
+                    itemBuilder: (BuildContext context) => <PopupMenuItem<String>>[
+                      _buildMenuItem(Icons.share, 'Tweet recipe'),
+                      _buildMenuItem(Icons.email, 'Email recipe'),
+                      _buildMenuItem(Icons.message, 'Message recipe'),
+                      _buildMenuItem(Icons.people, 'Share on Facebook'),
+                    ],
+                  ),
+                ],
+                flexibleSpace: new FlexibleSpaceBar(
+                  background: new DecoratedBox(
+                    decoration: new BoxDecoration(
+                      gradient: new LinearGradient(
+                        begin: const FractionalOffset(0.5, 0.0),
+                        end: const FractionalOffset(0.5, 0.40),
+                        colors: <Color>[const Color(0x60000000), const Color(0x00000000)],
+                      ),
+                    ),
+                  ),
+                ),
+              ),
+              new SliverToBoxAdapter(
                 child: new Stack(
                   children: <Widget>[
                     new Container(
-                      padding: new EdgeInsets.only(top: _kFabHalfSize),
+                      padding: const EdgeInsets.only(top: _kFabHalfSize),
                       width: fullWidth ? null : _kRecipePageMaxWidth,
                       child: new RecipeSheet(recipe: config.recipe),
                     ),
@@ -386,12 +377,12 @@ class _RecipePageState extends State<RecipePage> {
                       ),
                     ),
                   ],
-                ),
+                )
               ),
-            ),
+            ],
           ),
-        ),
-      ],
+        ],
+      ),
     );
   }
 

examples/flutter_gallery/lib/demo/shrine/shrine_page.dart

@@ -40,8 +40,8 @@ class ShrinePage extends StatefulWidget {
 class ShrinePageState extends State<ShrinePage> {
   int _appBarElevation = 0;
 
-  bool _handleScrollNotification(ScrollNotification notification) {
-    int elevation = notification.scrollable.scrollOffset <= 0.0 ? 0 : 1;
+  bool _handleScrollNotification(ScrollNotification2 notification) {
+    int elevation = notification.metrics.extentBefore <= 0.0 ? 0 : 1;
     if (elevation != _appBarElevation) {
       setState(() {
         _appBarElevation = elevation;
@@ -141,7 +141,7 @@ class ShrinePageState extends State<ShrinePage> {
         ]
       ),
       floatingActionButton: config.floatingActionButton,
-      body: new NotificationListener<ScrollNotification>(
+      body: new NotificationListener<ScrollNotification2>(
         onNotification: _handleScrollNotification,
         child: config.body
       )

examples/flutter_gallery/lib/gallery/home.dart

@@ -41,16 +41,13 @@ class _AppBarBackground extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    // TODO(abarth): Wire up to the parallax of the FlexibleSpaceBar in a way
-    // that doesn't pop during hero transition.
-    Animation<double> effectiveAnimation = kAlwaysDismissedAnimation;
     return new AnimatedBuilder(
-      animation: effectiveAnimation,
+      animation: animation,
       builder: (BuildContext context, Widget child) {
         return new Stack(
           children: _kBackgroundLayers.map((_BackgroundLayer layer) {
             return new Positioned(
-              top: -layer.parallaxTween.evaluate(effectiveAnimation),
+              top: -layer.parallaxTween.evaluate(animation),
               left: 0.0,
               right: 0.0,
               bottom: 0.0,
@@ -107,7 +104,6 @@ class GalleryHome extends StatefulWidget {
 
 class GalleryHomeState extends State<GalleryHome> with SingleTickerProviderStateMixin {
   static final GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState>();
-  static final GlobalKey<ScrollableState> _scrollableKey = new GlobalKey<ScrollableState>();
 
   AnimationController _controller;
 
@@ -153,10 +149,8 @@ class GalleryHomeState extends State<GalleryHome> with SingleTickerProviderState
 
   @override
   Widget build(BuildContext context) {
-    final double statusBarHeight = MediaQuery.of(context).padding.top;
     Widget home = new Scaffold(
       key: _scaffoldKey,
-      scrollableKey: _scrollableKey,
       drawer: new GalleryDrawer(
         useLightTheme: config.useLightTheme,
         onThemeChanged: config.onThemeChanged,
@@ -169,27 +163,19 @@ class GalleryHomeState extends State<GalleryHome> with SingleTickerProviderState
         onPlatformChanged: config.onPlatformChanged,
         onSendFeedback: config.onSendFeedback,
       ),
-      appBar: new AppBar(
-        expandedHeight: _kFlexibleSpaceMaxHeight,
-        flexibleSpace: new FlexibleSpaceBar(
-          title: new Text('Flutter Gallery'),
-          background: new Builder(
-            builder: (BuildContext context) {
-              return new _AppBarBackground(
-                animation: _scaffoldKey.currentState.appBarAnimation
-              );
-            }
-          )
-        )
-      ),
-      appBarBehavior: AppBarBehavior.under,
-      // The block's padding just exists to occupy the space behind the flexible app bar.
-      // As the block's padded region is scrolled upwards, the app bar's height will
-      // shrink keep it above the block content's and over the padded region.
-      body: new Block(
-       scrollableKey: _scrollableKey,
-       padding: new EdgeInsets.only(top: _kFlexibleSpaceMaxHeight + statusBarHeight),
-       children: _galleryListItems()
+      body: new CustomScrollView(
+        slivers: <Widget>[
+          new SliverAppBar(
+            pinned: true,
+            expandedHeight: _kFlexibleSpaceMaxHeight,
+            flexibleSpace: new FlexibleSpaceBar(
+              title: new Text('Flutter Gallery'),
+              // TODO(abarth): Wire up to the parallax in a way that doesn't pop during hero transition.
+              background: new _AppBarBackground(animation: kAlwaysDismissedAnimation),
+            ),
+          ),
+          new SliverList(delegate: new SliverChildListDelegate(_galleryListItems())),
+        ],
       )
     );
 

examples/flutter_gallery/test/example_code_display_test.dart

@@ -21,11 +21,12 @@ void main() {
 
     // Scroll the Buttons demo into view so that a tap will succeed
     final Point allDemosOrigin = tester.getTopRight(find.text('Demos'));
-    final Point buttonsDemoOrigin = tester.getTopRight(find.text('Buttons'));
-    final double scrollDelta  = buttonsDemoOrigin.y - allDemosOrigin.y;
-    await tester.scrollAt(allDemosOrigin, new Offset(0.0, -scrollDelta));
-    await tester.pump(); // start the scroll
-    await tester.pump(const Duration(seconds: 1));
+    final Finder button = find.text('Buttons');
+    while (button.evaluate().isEmpty) {
+      await tester.scrollAt(allDemosOrigin, new Offset(0.0, -100.0));
+      await tester.pump(); // start the scroll
+      await tester.pump(const Duration(seconds: 1));
+    }
 
     // Launch the buttons demo and then prove that showing the example
     // code dialog does not crash.

examples/flutter_gallery/test/smoke_test.dart

@@ -38,6 +38,7 @@ Future<Null> smokeDemo(WidgetTester tester, String routeName) async {
   await tester.pump(const Duration(seconds: 1)); // Wait until the demo has opened.
 
   expect(find.text(kCaption), findsNothing);
+  await tester.pump(const Duration(seconds: 1)); // Leave the demo on the screen briefly for manual testing.
 
   // Go back
   Finder backButton = find.byTooltip('Back');
@@ -61,22 +62,12 @@ Future<Null> runSmokeTest(WidgetTester tester) async {
 
   expect(find.text(kCaption), findsOneWidget);
 
-  final List<double> scrollDeltas = new List<double>();
-  double previousY = tester.getTopRight(find.text(demoCategories[0])).y;
   for (String routeName in routeNames) {
-    final double y = tester.getTopRight(findGalleryItemByRouteName(tester, routeName)).y;
-    scrollDeltas.add(previousY - y);
-    previousY = y;
-  }
-
-  // Launch each demo and then scroll that item out of the way.
-  for (int i = 0; i < routeNames.length; i += 1) {
-    final String routeName = routeNames[i];
+    Finder finder = findGalleryItemByRouteName(tester, routeName);
+    Scrollable2.ensureVisible(tester.element(finder), alignment: 0.5);
+    await tester.pump();
+    await tester.pumpUntilNoTransientCallbacks();
     await smokeDemo(tester, routeName);
-    await tester.scroll(findGalleryItemByRouteName(tester, routeName), new Offset(0.0, scrollDeltas[i]));
-    await tester.pump(); // start the scroll
-    await tester.pump(const Duration(milliseconds: 500)); // wait for overscroll to timeout, if necessary
-    await tester.pump(const Duration(seconds: 3)); // wait for overscroll to fade away, if necessary
     tester.binding.debugAssertNoTransientCallbacks('A transient callback was still active after leaving route $routeName');
   }
 

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

@@ -4,33 +4,32 @@
 
 import 'dart:math' as math;
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/widgets.dart';
 
-import 'app_bar.dart';
 import 'constants.dart';
-import 'scaffold.dart';
 import 'theme.dart';
 
 /// The part of a material design [AppBar] that expands and collapses.
 ///
-/// Most commonly used in in the [AppBar.flexibleSpace] field, a flexible space
-/// bar expands and contracts as the app scrolls so that the [AppBar] reaches
-/// from the top of the app to the top of the scrolling contents of the app.
+/// Most commonly used in in the [SliverAppBar.flexibleSpace] field, a flexible
+/// space bar expands and contracts as the app scrolls so that the [AppBar]
+/// reaches from the top of the app to the top of the scrolling contents of the
+/// app.
 ///
-/// Requires one of its ancestors to be a [Scaffold] widget because the
-/// [Scaffold] coordinates the scrolling effect between the flexible space and
-/// its body.
+/// The widget that sizes the [AppBar] must wrap it in the widget returned by
+/// [FlexibleSpaceBar.createSettings], to convey sizing information down to the
+/// [FlexibleSpaceBar].
 ///
 /// See also:
 ///
-///  * [AppBar]
-///  * [Scaffold]
+///  * [SliverAppBar], which implements the expanding and contracting.
+///  * [AppBar], which is used by [SliverAppBar].
 ///  * <https://material.google.com/patterns/scrolling-techniques.html>
 class FlexibleSpaceBar extends StatefulWidget {
   /// Creates a flexible space bar.
   ///
-  /// Most commonly used in the [AppBar.flexibleSpace] field. Requires one of
-  /// its ancestors to be a [Scaffold] widget.
+  /// Most commonly used in the [AppBar.flexibleSpace] field.
   FlexibleSpaceBar({
     Key key,
     this.title,
@@ -53,6 +52,23 @@ class FlexibleSpaceBar extends StatefulWidget {
   /// Defaults to being adapted to the current [TargetPlatform].
   final bool centerTitle;
 
+  static Widget createSettings({
+    double toolbarOpacity,
+    double minExtent,
+    double maxExtent,
+    @required double currentExtent,
+    @required Widget child,
+  }) {
+    assert(currentExtent != null);
+    return new _FlexibleSpaceBarSettings(
+      toolbarOpacity: toolbarOpacity ?? 1.0,
+      minExtent: minExtent ?? currentExtent,
+      maxExtent: maxExtent ?? currentExtent,
+      currentExtent: currentExtent,
+      child: child,
+    );
+  }
+
   @override
   _FlexibleSpaceBarState createState() => new _FlexibleSpaceBarState();
 }
@@ -72,34 +88,32 @@ class _FlexibleSpaceBarState extends State<FlexibleSpaceBar> {
     return null;
   }
 
-  Widget _buildContent(BuildContext context, BoxConstraints constraints) {
-    final Size size = constraints.biggest;
-    final double statusBarHeight = MediaQuery.of(context).padding.top;
+  @override
+  Widget build(BuildContext context) {
+    _FlexibleSpaceBarSettings settings = context.inheritFromWidgetOfExactType(_FlexibleSpaceBarSettings);
+    assert(settings != null, 'A FlexibleSpaceBar must be wrapped in the widget returned by FlexibleSpaceBar.createSettings().');
+
+    final List<Widget> children = <Widget>[];
 
-    final double currentHeight = size.height;
-    final double maxHeight = statusBarHeight + AppBar.getExpandedHeightFor(context);
-    final double minHeight = statusBarHeight + kToolbarHeight;
-    final double deltaHeight = maxHeight - minHeight;
+    final double deltaExtent = settings.maxExtent - settings.minExtent;
 
     // 0.0 -> Expanded
     // 1.0 -> Collapsed to toolbar
-    final double t = (1.0 - (currentHeight - minHeight) / deltaHeight).clamp(0.0, 1.0);
-
-    final List<Widget> children = <Widget>[];
+    final double t = (1.0 - (settings.currentExtent - settings.minExtent) / (deltaExtent)).clamp(0.0, 1.0);
 
     // background image
     if (config.background != null) {
-      final double fadeStart = math.max(0.0, 1.0 - kToolbarHeight / deltaHeight);
+      final double fadeStart = math.max(0.0, 1.0 - kToolbarHeight / deltaExtent);
       final double fadeEnd = 1.0;
       assert(fadeStart <= fadeEnd);
       final double opacity = 1.0 - new Interval(fadeStart, fadeEnd).transform(t);
-      final double parallax = new Tween<double>(begin: 0.0, end: deltaHeight / 4.0).lerp(t);
+      final double parallax = new Tween<double>(begin: 0.0, end: deltaExtent / 4.0).lerp(t);
       if (opacity > 0.0) {
         children.add(new Positioned(
           top: -parallax,
           left: 0.0,
           right: 0.0,
-          height: maxHeight,
+          height: settings.maxExtent,
           child: new Opacity(
             opacity: opacity,
             child: config.background
@@ -110,7 +124,7 @@ class _FlexibleSpaceBarState extends State<FlexibleSpaceBar> {
 
     if (config.title != null) {
       final ThemeData theme = Theme.of(context);
-      final double opacity = (1.0 - (minHeight - currentHeight) / (kToolbarHeight - statusBarHeight)).clamp(0.0, 1.0);
+      final double opacity = settings.toolbarOpacity;
       if (opacity > 0.0) {
         TextStyle titleStyle = theme.primaryTextTheme.title;
         titleStyle = titleStyle.copyWith(
@@ -140,9 +154,28 @@ class _FlexibleSpaceBarState extends State<FlexibleSpaceBar> {
 
     return new ClipRect(child: new Stack(children: children));
   }
+}
+
+class _FlexibleSpaceBarSettings extends InheritedWidget {
+  _FlexibleSpaceBarSettings({
+    Key key,
+    this.toolbarOpacity,
+    this.minExtent,
+    this.maxExtent,
+    this.currentExtent,
+    Widget child,
+  }) : super(key: key, child: child);
+
+  final double toolbarOpacity;
+  final double minExtent;
+  final double maxExtent;
+  final double currentExtent;
 
   @override
-  Widget build(BuildContext context) {
-    return new LayoutBuilder(builder: _buildContent);
+  bool updateShouldNotify(_FlexibleSpaceBarSettings oldWidget) {
+    return toolbarOpacity != oldWidget.toolbarOpacity
+        || minExtent != oldWidget.minExtent
+        || maxExtent != oldWidget.maxExtent
+        || currentExtent != oldWidget.currentExtent;
   }
 }

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

@@ -473,6 +473,7 @@ class SemanticsNode extends AbstractNode {
     owner._nodes.remove(id);
     owner._detachedNodes.add(this);
     super.detach();
+    assert(owner == null);
     if (_children != null) {
       for (SemanticsNode child in _children) {
         // The list of children may be stale and may contain nodes that have
@@ -481,6 +482,10 @@ class SemanticsNode extends AbstractNode {
           child.detach();
       }
     }
+    // The other side will have forgotten this node if we ever send
+    // it again, so make sure to mark it dirty so that it'll get
+    // sent if it is resurrected.
+    _markDirty();
   }
 
   bool _dirty = false;
@@ -563,7 +568,7 @@ class SemanticsNode extends AbstractNode {
     StringBuffer buffer = new StringBuffer();
     buffer.write('$runtimeType($id');
     if (_dirty)
-      buffer.write(" (${ owner != null && owner._dirtyNodes.contains(this) ? 'dirty' : 'STALE' })");
+      buffer.write(' (${ owner != null && owner._dirtyNodes.contains(this) ? "dirty" : "STALE; owner=$owner" })');
     if (_shouldMergeAllDescendantsIntoThisNode)
       buffer.write(' (leaf merge)');
     buffer.write('; $rect');
@@ -624,19 +629,13 @@ class SemanticsOwner extends ChangeNotifier {
 
   /// Update the semantics using [ui.window.updateSemantics].
   void sendSemanticsUpdate() {
-    for (SemanticsNode oldNode in _detachedNodes) {
-      // The other side will have forgotten this node if we even send
-      // it again, so make sure to mark it dirty so that it'll get
-      // sent if it is resurrected.
-      oldNode._dirty = true;
-    }
-    _detachedNodes.clear();
     if (_dirtyNodes.isEmpty)
       return;
     List<SemanticsNode> visitedNodes = <SemanticsNode>[];
     while (_dirtyNodes.isNotEmpty) {
-      List<SemanticsNode> localDirtyNodes = _dirtyNodes.toList();
+      List<SemanticsNode> localDirtyNodes = _dirtyNodes.where((SemanticsNode node) => !_detachedNodes.contains(node)).toList();
       _dirtyNodes.clear();
+      _detachedNodes.clear();
       localDirtyNodes.sort((SemanticsNode a, SemanticsNode b) => a.depth - b.depth);
       visitedNodes.addAll(localDirtyNodes);
       for (SemanticsNode node in localDirtyNodes) {
@@ -759,4 +758,7 @@ class SemanticsOwner extends ChangeNotifier {
     SemanticsActionHandler handler = _getSemanticsActionHandlerForPosition(node, position, action);
     handler?.performAction(action);
   }
+
+  @override
+  String toString() => '$runtimeType@$hashCode';
 }

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

@@ -20,16 +20,19 @@ abstract class RenderSliverPersistentHeader extends RenderSliver with RenderObje
     this.child = child;
   }
 
+  /// The biggest that this render object can become, in the main axis direction.
+  ///
+  /// This value should not be based on the child. If it changes, call
+  /// [markNeedsLayout].
   double get maxExtent;
 
-  /// The intrinsic size of the child as of the last time the sliver was laid out.
+  /// The smallest that this render object can become, in the main axis direction.
   ///
-  /// If the render object is dirty (i.e. if [markNeedsLayout] has been called,
-  /// or if the object was newly created), then the returned value will be stale
-  /// until [layoutChild] has been called.
-  @protected
-  double get minExtent => _minExtent;
-  double _minExtent;
+  /// If this is based on the intrinsic dimensions of the child, the child
+  /// should be measured during [updateChild] and the value cached and returned
+  /// here. The [updateChild] method will automatically be invoked any time the
+  /// child changes its intrinsic dimensions.
+  double get minExtent;
 
   @protected
   double get childExtent {
@@ -46,69 +49,65 @@ abstract class RenderSliverPersistentHeader extends RenderSliver with RenderObje
     return null;
   }
 
-  @protected
-  double _getChildIntrinsicExtent() {
-    if (child == null)
-      return 0.0;
-    assert(child != null);
-    assert(constraints.axis != null);
-    switch (constraints.axis) {
-      case Axis.vertical:
-        return child.getMinIntrinsicHeight(constraints.crossAxisExtent);
-      case Axis.horizontal:
-        return child.getMinIntrinsicWidth(constraints.crossAxisExtent);
-    }
-    return null;
-  }
+  bool _needsUpdateChild = true;
+  double _lastShrinkOffset = 0.0;
+  bool _lastOverlapsContent = false;
 
-  /// The last value that we passed to updateChild().
-  double _lastShrinkOffset;
-
-  /// Called during layout if the shrink offset has changed.
+  /// Update the child render object if necessary.
   ///
-  /// During this callback, the [child] can be set, mutated, or replaced.
-  @protected
-  void updateChild(double shrinkOffset) { }
-
-  /// Flag the current child as stale and needing updating even if the shrink
-  /// offset has not changed.
+  /// Called before the first layout, any time [markNeedsLayout] is called, and
+  /// any time the scroll offset changes. The `shrinkOffset` is the difference
+  /// between the [maxExtent] and the current size. Zero means the header is
+  /// fully expanded, any greater number up to [maxExtent] means that the header
+  /// has been scrolled by that much. The `overlapsContent` argument is true if
+  /// the sliver's leading edge is beyond its normal place in the viewport
+  /// contents, and false otherwise. It may still paint beyond its normal place
+  /// if the [minExtent] after this call is greater than the amount of space that
+  /// would normally be left.
+  ///
+  /// The render object will size itself to the larger of (a) the [maxExtent]
+  /// minus the child's intrinsic height and (b) the [maxExtent] minus the
+  /// shrink offset.
   ///
-  /// Call this whenever [updateChild] would change or mutate the child even if
-  /// given the same `shrinkOffset` as the last time it was called.
+  /// When this method is called by [layoutChild], the [child] can be set,
+  /// mutated, or replaced. (It should not be called outside [layoutChild].)
   ///
-  /// This must be implemented by [RenderSliverPersistentHeader] subclasses such
-  /// that the next layout after this call will result in [updateChild] being
-  /// called.
+  /// Any time this method would mutate the child, call [markNeedsLayout].
   @protected
-  void markNeedsUpdate() {
-    markNeedsLayout();
-    _lastShrinkOffset = null;
+  void updateChild(double shrinkOffset, bool overlapsContent) { }
+
+  @override
+  void markNeedsLayout() {
+    // This is automatically called whenever the child's intrinsic dimensions
+    // change, at which point we should remeasure them during the next layout.
+    _needsUpdateChild = true;
+    super.markNeedsLayout();
   }
 
-  void layoutChild(double scrollOffset, double maxExtent) {
+  void layoutChild(double scrollOffset, double maxExtent, { bool overlapsContent: false }) {
     assert(maxExtent != null);
     final double shrinkOffset = math.min(scrollOffset, maxExtent);
-    if (shrinkOffset != _lastShrinkOffset) {
+    if (_needsUpdateChild || _lastShrinkOffset != shrinkOffset || _lastOverlapsContent != overlapsContent) {
       invokeLayoutCallback<SliverConstraints>((SliverConstraints constraints) {
         assert(constraints == this.constraints);
-        updateChild(shrinkOffset);
-        _minExtent = _getChildIntrinsicExtent();
+        updateChild(shrinkOffset, overlapsContent);
       });
       _lastShrinkOffset = shrinkOffset;
+      _lastOverlapsContent = overlapsContent;
+      _needsUpdateChild = false;
     }
-    assert(_minExtent != null);
+    assert(minExtent != null);
     assert(() {
-      if (_minExtent <= maxExtent)
+      if (minExtent <= maxExtent)
         return true;
       throw new FlutterError(
-        'The maxExtent for this $runtimeType is less than the child\'s intrinsic extent.\n'
+        'The maxExtent for this $runtimeType is less than its minExtent.\n'
         'The specified maxExtent was: ${maxExtent.toStringAsFixed(1)}\n'
-        'The child was updated with shrink offset: ${shrinkOffset.toStringAsFixed(1)}\n'
-        'The actual measured intrinsic extent of the child was: ${_minExtent.toStringAsFixed(1)}\n'
+        'The specified minExtent was: ${minExtent.toStringAsFixed(1)}\n'
       );
     });
     child?.layout(
-      constraints.asBoxConstraints(maxExtent: math.max(_minExtent, maxExtent - shrinkOffset)),
+      constraints.asBoxConstraints(maxExtent: math.max(minExtent, maxExtent - shrinkOffset)),
       parentUsesSize: true,
     );
   }
@@ -237,7 +236,7 @@ abstract class RenderSliverPinnedPersistentHeader extends RenderSliverPersistent
   @override
   void performLayout() {
     final double maxExtent = this.maxExtent;
-    layoutChild(constraints.scrollOffset + constraints.overlap, maxExtent);
+    layoutChild(constraints.scrollOffset + constraints.overlap, maxExtent, overlapsContent: constraints.overlap > 0.0);
     geometry = new SliverGeometry(
       scrollExtent: maxExtent,
       paintExtent: math.min(constraints.overlap + childExtent, constraints.remainingPaintExtent),
@@ -285,7 +284,7 @@ abstract class RenderSliverFloatingPersistentHeader extends RenderSliverPersiste
     } else {
       _effectiveScrollOffset = constraints.scrollOffset;
     }
-    layoutChild(_effectiveScrollOffset, maxExtent);
+    layoutChild(_effectiveScrollOffset, maxExtent, overlapsContent: _effectiveScrollOffset < constraints.scrollOffset);
     final double paintExtent = maxExtent - _effectiveScrollOffset;
     final double layoutExtent = (maxExtent - constraints.scrollOffset).clamp(0.0, constraints.remainingPaintExtent);
     geometry = new SliverGeometry(

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

@@ -155,9 +155,7 @@ class _WidgetsAppState extends State<WidgetsApp> implements WidgetsBindingObserv
     assert(mounted);
     NavigatorState navigator = _navigator.currentState;
     assert(navigator != null);
-    if (!await navigator.willPop())
-      return true;
-    return mounted && navigator.pop();
+    return await navigator.maybePop();
   }
 
   @override

packages/flutter/lib/src/widgets/primary_scroll_controller.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/foundation.dart';
+
+import 'framework.dart';
+import 'scroll_controller.dart';
+
+class PrimaryScrollController extends InheritedWidget {
+  PrimaryScrollController({
+    Key key,
+    @required this.controller,
+    @required Widget child
+  }) : super(key: key, child: child) {
+    assert(controller != null);
+  }
+
+  final ScrollController controller;
+
+  static ScrollController of(BuildContext context) {
+    PrimaryScrollController result = context.inheritFromWidgetOfExactType(PrimaryScrollController);
+    return result?.controller;
+  }
+
+  @override
+  bool updateShouldNotify(PrimaryScrollController old) => controller != old.controller;
+
+  @override
+  void debugFillDescription(List<String> description) {
+    super.debugFillDescription(description);
+    description.add('$controller');
+  }
+}

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

@@ -295,7 +295,10 @@ abstract class LocalHistoryRoute<T> extends Route<T> {
     assert(entry._owner == null);
     entry._owner = this;
     _localHistory ??= <LocalHistoryEntry>[];
+    final bool wasEmpty = _localHistory.isEmpty;
     _localHistory.add(entry);
+    if (wasEmpty)
+      changedInternalState();
   }
 
   /// Remove a local history entry from this route.
@@ -308,6 +311,8 @@ abstract class LocalHistoryRoute<T> extends Route<T> {
     _localHistory.remove(entry);
     entry._owner = null;
     entry._notifyRemoved();
+    if (_localHistory.isEmpty)
+      changedInternalState();
   }
 
   @override
@@ -317,6 +322,8 @@ abstract class LocalHistoryRoute<T> extends Route<T> {
       assert(entry._owner == this);
       entry._owner = null;
       entry._notifyRemoved();
+      if (_localHistory.isEmpty)
+        changedInternalState();
       return false;
     }
     return super.didPop(result);
@@ -326,26 +333,40 @@ abstract class LocalHistoryRoute<T> extends Route<T> {
   bool get willHandlePopInternally {
     return _localHistory != null && _localHistory.isNotEmpty;
   }
+
+  /// Called whenever the internal state of the route has changed.
+  ///
+  /// This should be called whenever [willHandlePopInternally] and [didPop]
+  /// might change the value they return. It is used by [ModalRoute], for
+  /// example, to report the new information via its inherited widget to any
+  /// children of the route.
+  @protected
+  @mustCallSuper
+  void changedInternalState() { }
 }
 
 class _ModalScopeStatus extends InheritedWidget {
   _ModalScopeStatus({
     Key key,
-    this.isCurrent,
-    this.route,
+    @required this.isCurrent,
+    @required this.canPop,
+    @required this.route,
     @required Widget child
   }) : super(key: key, child: child) {
     assert(isCurrent != null);
+    assert(canPop != null);
     assert(route != null);
     assert(child != null);
   }
 
   final bool isCurrent;
+  final bool canPop;
   final Route<dynamic> route;
 
   @override
   bool updateShouldNotify(_ModalScopeStatus old) {
     return isCurrent != old.isCurrent ||
+           canPop != old.canPop ||
            route != old.route;
   }
 
@@ -353,6 +374,8 @@ class _ModalScopeStatus extends InheritedWidget {
   void debugFillDescription(List<String> description) {
     super.debugFillDescription(description);
     description.add('${isCurrent ? "active" : "inactive"}');
+    if (canPop)
+      description.add('can pop');
   }
 }
 
@@ -396,7 +419,6 @@ class _ModalScopeState extends State<_ModalScope> {
   void dispose() {
     config.route.animation?.removeStatusListener(_animationStatusChanged);
     config.route.forwardAnimation?.removeStatusListener(_animationStatusChanged);
-    willPopCallbacks = null;
     super.dispose();
   }
 
@@ -439,13 +461,14 @@ class _ModalScopeState extends State<_ModalScope> {
                 child: new _ModalScopeStatus(
                   route: config.route,
                   isCurrent: config.route.isCurrent,
-                  child: config.page
-                )
-              )
-            )
-          )
-        )
-      )
+                  canPop: config.route.canPop(),
+                  child: config.page,
+                ),
+              ),
+            ),
+          ),
+        ),
+      ),
     );
   }
 }
@@ -734,6 +757,24 @@ abstract class ModalRoute<T> extends TransitionRoute<T> with LocalHistoryRoute<T
     return _scopeKey.currentState == null || _scopeKey.currentState.willPopCallbacks.length > 0;
   }
 
+  @override
+  void changedInternalState() {
+    super.changedInternalState();
+    setState(() { /* internal state already changed */ });
+  }
+
+  @override
+  void didChangePrevious(Route<dynamic> route) {
+    super.didChangePrevious(route);
+    setState(() { /* this might affect canPop */ });
+  }
+
+  /// Whether this route can be popped.
+  ///
+  /// When this changes, the route will rebuild, and any widgets that used
+  /// [ModalRoute.of] will be notified.
+  bool canPop() => !isFirst || willHandlePopInternally;
+
   // Internals
 
   final GlobalKey<_ModalScopeState> _scopeKey = new GlobalKey<_ModalScopeState>();

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

@@ -22,6 +22,14 @@ class ScrollController {
 
   final List<ScrollPosition> _positions = <ScrollPosition>[];
 
+  /// Whether any [ScrollPosition] objects have attached themselves to the
+  /// [ScrollController] using the [attach] method.
+  ///
+  /// If this is false, then members that interact with the [ScrollPosition],
+  /// such as [position], [offset], [animateTo], and [jumpTo], must not be
+  /// called.
+  bool get hasClients => _positions.isNotEmpty;
+
   ScrollPosition get position {
     assert(_positions.isNotEmpty, 'ScrollController not attached to any scroll views.');
     assert(_positions.length == 1, 'ScrollController attached to multiple scroll views.');

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

@@ -5,8 +5,9 @@
 import 'package:flutter/rendering.dart';
 import 'package:meta/meta.dart';
 
-import 'framework.dart';
 import 'basic.dart';
+import 'framework.dart';
+import 'primary_scroll_controller.dart';
 import 'scroll_controller.dart';
 import 'scroll_physics.dart';
 import 'scroll_position.dart';
@@ -20,11 +21,16 @@ abstract class ScrollView extends StatelessWidget {
     this.scrollDirection: Axis.vertical,
     this.reverse: false,
     this.controller,
+    this.primary: false,
     this.physics,
     this.shrinkWrap: false,
   }) : super(key: key) {
     assert(reverse != null);
     assert(shrinkWrap != null);
+    assert(primary != null);
+    assert(controller == null || !primary,
+           'Primary ScrollViews obtain their ScrollController via inheritance from a PrimaryScrollController widget. '
+           'You cannot both set primary to true and pass an explicit controller.');
   }
 
   final Axis scrollDirection;
@@ -33,6 +39,8 @@ abstract class ScrollView extends StatelessWidget {
 
   final ScrollController controller;
 
+  final bool primary;
+
   final ScrollPhysics physics;
 
   final bool shrinkWrap;
@@ -58,7 +66,7 @@ abstract class ScrollView extends StatelessWidget {
     AxisDirection axisDirection = getDirection(context);
     return new Scrollable2(
       axisDirection: axisDirection,
-      controller: controller,
+      controller: controller ?? (primary ? PrimaryScrollController.of(context) : null),
       physics: physics,
       viewportBuilder: (BuildContext context, ViewportOffset offset) {
         if (shrinkWrap) {
@@ -82,6 +90,14 @@ abstract class ScrollView extends StatelessWidget {
   void debugFillDescription(List<String> description) {
     super.debugFillDescription(description);
     description.add('$scrollDirection');
+    if (reverse)
+      description.add('reversed');
+    if (controller != null)
+      description.add('$controller');
+    if (primary)
+      description.add('using primary controller');
+    if (physics != null)
+      description.add('$physics');
     if (shrinkWrap)
       description.add('shrink-wrapping');
   }
@@ -93,6 +109,7 @@ class CustomScrollView extends ScrollView {
     Axis scrollDirection: Axis.vertical,
     bool reverse: false,
     ScrollController controller,
+    bool primary: false,
     ScrollPhysics physics,
     bool shrinkWrap: false,
     this.slivers: const <Widget>[],
@@ -101,6 +118,7 @@ class CustomScrollView extends ScrollView {
     scrollDirection: scrollDirection,
     reverse: reverse,
     controller: controller,
+    primary: primary,
     physics: physics,
     shrinkWrap: shrinkWrap,
   );
@@ -117,6 +135,7 @@ abstract class BoxScrollView extends ScrollView {
     Axis scrollDirection: Axis.vertical,
     bool reverse: false,
     ScrollController controller,
+    bool primary: false,
     ScrollPhysics physics,
     bool shrinkWrap: false,
     this.padding,
@@ -125,6 +144,7 @@ abstract class BoxScrollView extends ScrollView {
     scrollDirection: scrollDirection,
     reverse: reverse,
     controller: controller,
+    primary: primary,
     physics: physics,
     shrinkWrap: shrinkWrap,
   );
@@ -164,6 +184,7 @@ class ListView extends BoxScrollView {
     Axis scrollDirection: Axis.vertical,
     bool reverse: false,
     ScrollController controller,
+    bool primary: false,
     ScrollPhysics physics,
     bool shrinkWrap: false,
     EdgeInsets padding,
@@ -174,6 +195,7 @@ class ListView extends BoxScrollView {
     scrollDirection: scrollDirection,
     reverse: reverse,
     controller: controller,
+    primary: primary,
     physics: physics,
     shrinkWrap: shrinkWrap,
     padding: padding,
@@ -184,6 +206,7 @@ class ListView extends BoxScrollView {
     Axis scrollDirection: Axis.vertical,
     bool reverse: false,
     ScrollController controller,
+    bool primary: false,
     ScrollPhysics physics,
     bool shrinkWrap: false,
     EdgeInsets padding,
@@ -195,6 +218,7 @@ class ListView extends BoxScrollView {
     scrollDirection: scrollDirection,
     reverse: reverse,
     controller: controller,
+    primary: primary,
     physics: physics,
     shrinkWrap: shrinkWrap,
     padding: padding,
@@ -205,6 +229,7 @@ class ListView extends BoxScrollView {
     Axis scrollDirection: Axis.vertical,
     bool reverse: false,
     ScrollController controller,
+    bool primary: false,
     ScrollPhysics physics,
     bool shrinkWrap: false,
     EdgeInsets padding,
@@ -215,6 +240,7 @@ class ListView extends BoxScrollView {
     scrollDirection: scrollDirection,
     reverse: reverse,
     controller: controller,
+    primary: primary,
     physics: physics,
     shrinkWrap: shrinkWrap,
     padding: padding,
@@ -259,6 +285,7 @@ class GridView extends BoxScrollView {
     Axis scrollDirection: Axis.vertical,
     bool reverse: false,
     ScrollController controller,
+    bool primary: false,
     ScrollPhysics physics,
     bool shrinkWrap: false,
     EdgeInsets padding,
@@ -269,6 +296,7 @@ class GridView extends BoxScrollView {
     scrollDirection: scrollDirection,
     reverse: reverse,
     controller: controller,
+    primary: primary,
     physics: physics,
     shrinkWrap: shrinkWrap,
     padding: padding,
@@ -281,6 +309,7 @@ class GridView extends BoxScrollView {
     Axis scrollDirection: Axis.vertical,
     bool reverse: false,
     ScrollController controller,
+    bool primary: false,
     ScrollPhysics physics,
     bool shrinkWrap: false,
     EdgeInsets padding,
@@ -291,6 +320,7 @@ class GridView extends BoxScrollView {
     scrollDirection: scrollDirection,
     reverse: reverse,
     controller: controller,
+    primary: primary,
     physics: physics,
     shrinkWrap: shrinkWrap,
     padding: padding,
@@ -304,6 +334,7 @@ class GridView extends BoxScrollView {
     Axis scrollDirection: Axis.vertical,
     bool reverse: false,
     ScrollController controller,
+    bool primary: false,
     ScrollPhysics physics,
     bool shrinkWrap: false,
     EdgeInsets padding,
@@ -323,6 +354,7 @@ class GridView extends BoxScrollView {
     scrollDirection: scrollDirection,
     reverse: reverse,
     controller: controller,
+    primary: primary,
     physics: physics,
     shrinkWrap: shrinkWrap,
     padding: padding,
@@ -333,6 +365,7 @@ class GridView extends BoxScrollView {
     Axis scrollDirection: Axis.vertical,
     bool reverse: false,
     ScrollController controller,
+    bool primary: false,
     ScrollPhysics physics,
     bool shrinkWrap: false,
     EdgeInsets padding,
@@ -352,6 +385,7 @@ class GridView extends BoxScrollView {
     scrollDirection: scrollDirection,
     reverse: reverse,
     controller: controller,
+    primary: primary,
     physics: physics,
     shrinkWrap: shrinkWrap,
     padding: padding,

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

@@ -86,7 +86,12 @@ class Scrollable2 extends StatefulWidget {
 
     Scrollable2State scrollable = Scrollable2.of(context);
     while (scrollable != null) {
-      futures.add(scrollable.position.ensureVisible(context.findRenderObject(), alignment: alignment));
+      futures.add(scrollable.position.ensureVisible(
+        context.findRenderObject(),
+        alignment: alignment,
+        duration: duration,
+        curve: curve,
+      ));
       context = scrollable.context;
       scrollable = Scrollable2.of(context);
     }

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

@@ -12,7 +12,9 @@ abstract class SliverPersistentHeaderDelegate {
   /// const constructors so that they can be used in const expressions.
   const SliverPersistentHeaderDelegate();
 
-  Widget build(BuildContext context, double shrinkOffset);
+  Widget build(BuildContext context, double shrinkOffset, bool overlapsContent);
+
+  double get minExtent;
 
   double get maxExtent;
 
@@ -101,9 +103,9 @@ class _SliverPersistentHeaderElement extends RenderObjectElement {
 
   Element child;
 
-  void _build(double shrinkOffset) {
+  void _build(double shrinkOffset, bool overlapsContent) {
     owner.buildScope(this, () {
-      child = updateChild(child, widget.delegate.build(this, shrinkOffset), null);
+      child = updateChild(child, widget.delegate.build(this, shrinkOffset, overlapsContent), null);
     });
   }
 
@@ -160,18 +162,21 @@ abstract class _SliverPersistentHeaderRenderObjectWidget extends RenderObjectWid
 abstract class _RenderSliverPersistentHeaderForWidgetsMixin implements RenderSliverPersistentHeader {
   _SliverPersistentHeaderElement _element;
 
+  @override
+  double get minExtent => _element.widget.delegate.minExtent;
+
   @override
   double get maxExtent => _element.widget.delegate.maxExtent;
 
   @override
-  void updateChild(double shrinkOffset) {
+  void updateChild(double shrinkOffset, bool overlapsContent) {
     assert(_element != null);
-    _element._build(shrinkOffset);
+    _element._build(shrinkOffset, overlapsContent);
   }
 
   @protected
   void triggerRebuild() {
-    markNeedsUpdate();
+    markNeedsLayout();
   }
 }
 

packages/flutter/lib/widgets.dart

@@ -43,6 +43,7 @@ export 'src/widgets/page_view.dart';
 export 'src/widgets/pages.dart';
 export 'src/widgets/performance_overlay.dart';
 export 'src/widgets/placeholder.dart';
+export 'src/widgets/primary_scroll_controller.dart';
 export 'src/widgets/raw_keyboard_listener.dart';
 export 'src/widgets/routes.dart';
 export 'src/widgets/scroll_behavior.dart';

packages/flutter/test/material/scaffold_test.dart

@@ -80,32 +80,39 @@ void main() {
   testWidgets('Drawer scrolling', (WidgetTester tester) async {
     GlobalKey<ScrollableState<Scrollable>> drawerKey =
         new GlobalKey<ScrollableState<Scrollable>>(debugLabel: 'drawer');
-    Key appBarKey = new Key('appBar');
     const double appBarHeight = 256.0;
 
+    ScrollController scrollOffset = new ScrollController();
+
     await tester.pumpWidget(
       new MaterialApp(
         home: new Scaffold(
-          appBarBehavior: AppBarBehavior.under,
-          appBar: new AppBar(
-            key: appBarKey,
-            expandedHeight: appBarHeight,
-            title: new Text('Title'),
-            flexibleSpace: new FlexibleSpaceBar(title: new Text('Title')),
-          ),
           drawer: new Drawer(
-            child: new Block(
-              scrollableKey: drawerKey,
+            key: drawerKey,
+            child: new ListView(
+              controller: scrollOffset,
               children: new List<Widget>.generate(10,
                 (int index) => new SizedBox(height: 100.0, child: new Text('D$index'))
               )
             )
           ),
-          body: new Block(
-            padding: const EdgeInsets.only(top: appBarHeight),
-            children: new List<Widget>.generate(10,
-              (int index) => new SizedBox(height: 100.0, child: new Text('B$index'))
-            ),
+          body: new CustomScrollView(
+            slivers: <Widget>[
+              new SliverAppBar(
+                pinned: true,
+                expandedHeight: appBarHeight,
+                title: new Text('Title'),
+                flexibleSpace: new FlexibleSpaceBar(title: new Text('Title')),
+              ),
+              new SliverPadding(
+                padding: const EdgeInsets.only(top: appBarHeight),
+                child: new SliverList(
+                  delegate: new SliverChildListDelegate(new List<Widget>.generate(
+                    10, (int index) => new SizedBox(height: 100.0, child: new Text('B$index')),
+                  )),
+                ),
+              ),
+            ],
           ),
         )
       )
@@ -117,86 +124,62 @@ void main() {
     await tester.pump();
     await tester.pump(const Duration(seconds: 1));
 
-    expect(drawerKey.currentState.scrollOffset, equals(0));
+    expect(scrollOffset.offset, 0.0);
 
     const double scrollDelta = 80.0;
     await tester.scroll(find.byKey(drawerKey), const Offset(0.0, -scrollDelta));
     await tester.pump();
 
-    expect(drawerKey.currentState.scrollOffset, equals(scrollDelta));
+    expect(scrollOffset.offset, scrollDelta);
 
-    RenderBox renderBox = tester.renderObject(find.byKey(appBarKey));
+    RenderBox renderBox = tester.renderObject(find.byType(AppBar));
     expect(renderBox.size.height, equals(appBarHeight));
   });
 
-  testWidgets('Tapping the status bar scrolls to top on iOS', (WidgetTester tester) async {
-    final GlobalKey<ScrollableState> scrollableKey = new GlobalKey<ScrollableState>();
-    final Key appBarKey = new UniqueKey();
-
-    await tester.pumpWidget(
-      new MaterialApp(
-        theme: new ThemeData(platform: TargetPlatform.iOS),
-        home: new MediaQuery(
-          data: const MediaQueryData(padding: const EdgeInsets.only(top: 25.0)), // status bar
-          child: new Scaffold(
-            scrollableKey: scrollableKey,
-            appBar: new AppBar(
-              key: appBarKey,
-              title: new Text('Title')
-            ),
-            body: new Block(
-              scrollableKey: scrollableKey,
-              initialScrollOffset: 500.0,
-              children: new List<Widget>.generate(20,
-                (int index) => new SizedBox(height: 100.0, child: new Text('$index'))
-              )
-            )
-          )
-        )
-      )
+  Widget _buildStatusBarTestApp(TargetPlatform platform) {
+    return new MaterialApp(
+      theme: new ThemeData(platform: platform),
+      home: new MediaQuery(
+        data: const MediaQueryData(padding: const EdgeInsets.only(top: 25.0)), // status bar
+        child: new Scaffold(
+          body: new CustomScrollView(
+            primary: true,
+            slivers: <Widget>[
+              new SliverAppBar(
+                title: new Text('Title')
+              ),
+              new SliverList(
+                delegate: new SliverChildListDelegate(new List<Widget>.generate(
+                  20, (int index) => new SizedBox(height: 100.0, child: new Text('$index')),
+                )),
+              ),
+            ],
+          ),
+        ),
+      ),
     );
+  }
 
-    final ScrollableState scrollable = tester.state(find.byType(Scrollable));
-    expect(scrollable.scrollOffset, equals(500.0));
+  testWidgets('Tapping the status bar scrolls to top on iOS', (WidgetTester tester) async {
+    await tester.pumpWidget(_buildStatusBarTestApp(TargetPlatform.iOS));
+    final Scrollable2State scrollable = tester.state(find.byType(Scrollable2));
+    scrollable.position.jumpTo(500.0);
+    expect(scrollable.position.pixels, equals(500.0));
     await tester.tapAt(const Point(100.0, 10.0));
     await tester.pump();
     await tester.pump(const Duration(seconds: 1));
-    expect(scrollable.scrollOffset, equals(0.0));
+    expect(scrollable.position.pixels, equals(0.0));
   });
 
   testWidgets('Tapping the status bar does not scroll to top on Android', (WidgetTester tester) async {
-    final GlobalKey<ScrollableState> scrollableKey = new GlobalKey<ScrollableState>();
-    final Key appBarKey = new UniqueKey();
-
-    await tester.pumpWidget(
-      new MaterialApp(
-        theme: new ThemeData(platform: TargetPlatform.android),
-        home: new MediaQuery(
-          data: const MediaQueryData(padding: const EdgeInsets.only(top: 25.0)), // status bar
-          child: new Scaffold(
-            scrollableKey: scrollableKey,
-            appBar: new AppBar(
-              key: appBarKey,
-              title: new Text('Title')
-            ),
-            body: new Block(
-              scrollableKey: scrollableKey,
-              initialScrollOffset: 500.0,
-              children: new List<Widget>.generate(20,
-                (int index) => new SizedBox(height: 100.0, child: new Text('$index'))
-              )
-            )
-          )
-        )
-      )
-    );
-
-    final ScrollableState scrollable = tester.state(find.byType(Scrollable));
-    expect(scrollable.scrollOffset, equals(500.0));
+    await tester.pumpWidget(_buildStatusBarTestApp(TargetPlatform.android));
+    final Scrollable2State scrollable = tester.state(find.byType(Scrollable2));
+    scrollable.position.jumpTo(500.0);
+    expect(scrollable.position.pixels, equals(500.0));
     await tester.tapAt(const Point(100.0, 10.0));
     await tester.pump();
     await tester.pump(const Duration(seconds: 1));
-    expect(scrollable.scrollOffset, equals(500.0));
+    expect(scrollable.position.pixels, equals(500.0));
   });
 
   testWidgets('Bottom sheet cannot overlap app bar', (WidgetTester tester) async {

packages/flutter/test/material/will_pop_test.dart

@@ -13,12 +13,22 @@ class SamplePage extends StatefulWidget {
 }
 
 class SamplePageState extends State<SamplePage> {
+  ModalRoute<Null> _route;
+
+  Future<bool> _callback() async => willPopValue;
+
   @override
   void dependenciesChanged() {
     super.dependenciesChanged();
-    final ModalRoute<Null> route = ModalRoute.of(context);
-    if (route.isCurrent)
-      route.addScopedWillPopCallback(() async => willPopValue);
+    _route?.removeScopedWillPopCallback(_callback);
+    _route = ModalRoute.of(context);
+    _route?.addScopedWillPopCallback(_callback);
+  }
+
+  @override
+  void dispose() {
+    super.dispose();
+    _route?.removeScopedWillPopCallback(_callback);
   }
 
   @override
@@ -87,6 +97,9 @@ void main() {
       ),
     );
 
+    expect(find.byTooltip('Back'), findsNothing);
+    expect(find.text('Sample Page'), findsNothing);
+
     await tester.tap(find.text('X'));
     await tester.pump();
     await tester.pump(const Duration(seconds: 1));

packages/flutter/test/widgets/slivers_appbar_floating_test.dart

@@ -189,8 +189,11 @@ class TestDelegate extends SliverPersistentHeaderDelegate {
   double get maxExtent => 200.0;
 
   @override
-  Widget build(BuildContext context, double shrinkOffset) {
-    return new Container(constraints: new BoxConstraints(minHeight: maxExtent / 2.0, maxHeight: maxExtent));
+  double get minExtent => 100.0;
+
+  @override
+  Widget build(BuildContext context, double shrinkOffset, bool overlapsContent) {
+    return new Container(constraints: new BoxConstraints(minHeight: minExtent, maxHeight: maxExtent));
   }
 
   @override

packages/flutter/test/widgets/slivers_appbar_pinned_test.dart

@@ -184,8 +184,11 @@ class TestDelegate extends SliverPersistentHeaderDelegate {
   double get maxExtent => 200.0;
 
   @override
-  Widget build(BuildContext context, double shrinkOffset) {
-    return new Container(constraints: new BoxConstraints(minHeight: maxExtent / 2.0, maxHeight: maxExtent));
+  double get minExtent => 100.0;
+
+  @override
+  Widget build(BuildContext context, double shrinkOffset, bool overlapsContent) {
+    return new Container(constraints: new BoxConstraints(minHeight: minExtent, maxHeight: maxExtent));
   }
 
   @override

packages/flutter/test/widgets/slivers_appbar_scrolling_test.dart

@@ -74,7 +74,10 @@ class TestDelegate extends SliverPersistentHeaderDelegate {
   double get maxExtent => 200.0;
 
   @override
-  Widget build(BuildContext context, double shrinkOffset) {
+  double get minExtent => 200.0;
+
+  @override
+  Widget build(BuildContext context, double shrinkOffset, bool overlapsContent) {
     return new Container(height: maxExtent);
   }
 

packages/flutter/test/widgets/slivers_evil_test.dart

@@ -16,10 +16,13 @@ class TestSliverPersistentHeaderDelegate extends SliverPersistentHeaderDelegate
   double get maxExtent => _maxExtent;
 
   @override
-  Widget build(BuildContext context, double shrinkOffset) {
+  double get minExtent => 16.0;
+
+  @override
+  Widget build(BuildContext context, double shrinkOffset, bool overlapsContent) {
     return new Column(
       children: <Widget>[
-        new Container(height: 16.0),
+        new Container(height: minExtent),
         new Expanded(child: new Container()),
       ],
     );