Tapping status bar scrolls to top on IOS (#5425)

examples/flutter_gallery/lib/demo/cards_demo.dart

@@ -128,15 +128,18 @@ class TravelDestinationItem extends StatelessWidget {
 }
 
 class CardsDemo extends StatelessWidget {
+  static final GlobalKey<ScrollableState> _scrollableKey = new GlobalKey<ScrollableState>();
   static const String routeName = '/cards';
 
   @override
   Widget build(BuildContext context) {
     return new Scaffold(
+      scrollableKey: _scrollableKey,
       appBar: new AppBar(
         title: new Text('Travel stream')
       ),
       body: new ScrollableList(
+        scrollableKey: _scrollableKey,
         itemExtent: TravelDestinationItem.height,
         padding: const EdgeInsets.only(top: 8.0, left: 8.0, right: 8.0),
         children: destinations.map((TravelDestination destination) {

examples/flutter_gallery/lib/demo/colors_demo.dart

@@ -8,8 +8,9 @@ import 'package:flutter/widgets.dart';
 const double kColorItemHeight = 48.0;
 
 class ColorSwatch {
-  const ColorSwatch({ this.name, this.colors, this.accentColors, this.threshold: 900});
+  ColorSwatch({ this.name, this.colors, this.accentColors, this.threshold: 900});
 
+  final GlobalKey<ScrollableState> scrollableKey = new GlobalKey<ScrollableState>();
   final String name;
   final Map<int, Color> colors;
   final Map<int, Color> accentColors;
@@ -18,26 +19,26 @@ class ColorSwatch {
   bool get isValid => this.name != null && this.colors != null && threshold != null;
 }
 
-const List<ColorSwatch> colorSwatches = const <ColorSwatch>[
-  const ColorSwatch(name: 'RED', colors: Colors.red, accentColors: Colors.redAccent, threshold: 300),
-  const ColorSwatch(name: 'PINK', colors: Colors.pink, accentColors: Colors.pinkAccent, threshold: 200),
-  const ColorSwatch(name: 'PURPLE', colors: Colors.purple, accentColors: Colors.purpleAccent, threshold: 200),
-  const ColorSwatch(name: 'DEEP PURPLE', colors: Colors.deepPurple, accentColors: Colors.deepPurpleAccent, threshold: 200),
-  const ColorSwatch(name: 'INDIGO', colors: Colors.indigo, accentColors: Colors.indigoAccent, threshold: 200),
-  const ColorSwatch(name: 'BLUE', colors: Colors.blue, accentColors: Colors.blueAccent, threshold: 400),
-  const ColorSwatch(name: 'LIGHT BLUE', colors: Colors.lightBlue, accentColors: Colors.lightBlueAccent, threshold: 500),
-  const ColorSwatch(name: 'CYAN', colors: Colors.cyan, accentColors: Colors.cyanAccent, threshold: 600),
-  const ColorSwatch(name: 'TEAL', colors: Colors.teal, accentColors: Colors.tealAccent, threshold: 400),
-  const ColorSwatch(name: 'GREEN', colors: Colors.green, accentColors: Colors.greenAccent, threshold: 500),
-  const ColorSwatch(name: 'LIGHT GREEN', colors: Colors.lightGreen, accentColors: Colors.lightGreenAccent, threshold: 600),
-  const ColorSwatch(name: 'LIME', colors: Colors.lime, accentColors: Colors.limeAccent, threshold: 800),
-  const ColorSwatch(name: 'YELLOW', colors: Colors.yellow, accentColors: Colors.yellowAccent),
-  const ColorSwatch(name: 'AMBER', colors: Colors.amber, accentColors: Colors.amberAccent),
-  const ColorSwatch(name: 'ORANGE', colors: Colors.orange, accentColors: Colors.orangeAccent, threshold: 700),
-  const ColorSwatch(name: 'DEEP ORANGE', colors: Colors.deepOrange, accentColors: Colors.deepOrangeAccent, threshold: 400),
-  const ColorSwatch(name: 'BROWN', colors: Colors.brown, threshold: 200),
-  const ColorSwatch(name: 'GREY', colors: Colors.grey, threshold: 500),
-  const ColorSwatch(name: 'BLUE GREY', colors: Colors.blueGrey, threshold: 500)
+final List<ColorSwatch> colorSwatches = <ColorSwatch>[
+  new ColorSwatch(name: 'RED', colors: Colors.red, accentColors: Colors.redAccent, threshold: 300),
+  new ColorSwatch(name: 'PINK', colors: Colors.pink, accentColors: Colors.pinkAccent, threshold: 200),
+  new ColorSwatch(name: 'PURPLE', colors: Colors.purple, accentColors: Colors.purpleAccent, threshold: 200),
+  new ColorSwatch(name: 'DEEP PURPLE', colors: Colors.deepPurple, accentColors: Colors.deepPurpleAccent, threshold: 200),
+  new ColorSwatch(name: 'INDIGO', colors: Colors.indigo, accentColors: Colors.indigoAccent, threshold: 200),
+  new ColorSwatch(name: 'BLUE', colors: Colors.blue, accentColors: Colors.blueAccent, threshold: 400),
+  new ColorSwatch(name: 'LIGHT BLUE', colors: Colors.lightBlue, accentColors: Colors.lightBlueAccent, threshold: 500),
+  new ColorSwatch(name: 'CYAN', colors: Colors.cyan, accentColors: Colors.cyanAccent, threshold: 600),
+  new ColorSwatch(name: 'TEAL', colors: Colors.teal, accentColors: Colors.tealAccent, threshold: 400),
+  new ColorSwatch(name: 'GREEN', colors: Colors.green, accentColors: Colors.greenAccent, threshold: 500),
+  new ColorSwatch(name: 'LIGHT GREEN', colors: Colors.lightGreen, accentColors: Colors.lightGreenAccent, threshold: 600),
+  new ColorSwatch(name: 'LIME', colors: Colors.lime, accentColors: Colors.limeAccent, threshold: 800),
+  new ColorSwatch(name: 'YELLOW', colors: Colors.yellow, accentColors: Colors.yellowAccent),
+  new ColorSwatch(name: 'AMBER', colors: Colors.amber, accentColors: Colors.amberAccent),
+  new ColorSwatch(name: 'ORANGE', colors: Colors.orange, accentColors: Colors.orangeAccent, threshold: 700),
+  new ColorSwatch(name: 'DEEP ORANGE', colors: Colors.deepOrange, accentColors: Colors.deepOrangeAccent, threshold: 400),
+  new ColorSwatch(name: 'BROWN', colors: Colors.brown, threshold: 200),
+  new ColorSwatch(name: 'GREY', colors: Colors.grey, threshold: 500),
+  new ColorSwatch(name: 'BLUE GREY', colors: Colors.blueGrey, threshold: 500)
 ];
 
 
@@ -102,20 +103,43 @@ class ColorSwatchTabView extends StatelessWidget {
     }
 
     return new ScrollableList(
+      scrollableKey: swatch.scrollableKey,
       itemExtent: kColorItemHeight,
       children: colorItems
     );
   }
 }
 
-class ColorsDemo extends StatelessWidget {
+class ColorsDemo extends StatefulWidget {
+  ColorsDemo({ Key key }) : super(key: key);
+
   static const String routeName = '/colors';
 
+  @override
+  _ColorsDemoState createState() => new _ColorsDemoState();
+}
+
+class _ColorsDemoState extends State<ColorsDemo> {
+
+  ColorSwatch _selectedSwatch;
+
+  @override
+  void initState() {
+    super.initState();
+    _selectedSwatch = colorSwatches.first;
+  }
+
   @override
   Widget build(BuildContext context) {
     return new TabBarSelection<ColorSwatch>(
       values: colorSwatches,
+      onChanged: (ColorSwatch value) {
+        setState(() {
+          _selectedSwatch = value;
+       });
+      },
       child: new Scaffold(
+        scrollableKey: _selectedSwatch.scrollableKey,
         appBar: new AppBar(
           elevation: 0,
           title: new Text('Colors'),

examples/flutter_gallery/lib/demo/contacts_demo.dart

@@ -80,7 +80,8 @@ class ContactsDemo extends StatefulWidget {
 }
 
 class ContactsDemoState extends State<ContactsDemo> {
-  final GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState>();
+  static final GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState>();
+  static final GlobalKey<ScrollableState> _scrollableKey = new GlobalKey<ScrollableState>();
   final double _appBarHeight = 256.0;
   AppBarBehavior _appBarBehavior = AppBarBehavior.under;
 
@@ -94,6 +95,7 @@ class ContactsDemoState extends State<ContactsDemo> {
       ),
       child: new Scaffold(
         key: _scaffoldKey,
+        scrollableKey: _scrollableKey,
         appBarBehavior: _appBarBehavior,
         appBar: new AppBar(
           expandedHeight: _appBarHeight,
@@ -151,6 +153,7 @@ class ContactsDemoState extends State<ContactsDemo> {
         ),
         body: new Block(
           padding: new EdgeInsets.only(top: _appBarHeight + statusBarHeight),
+          scrollableKey: _scrollableKey,
           children: <Widget>[
             new _ContactCategory(
               icon: Icons.call,

examples/flutter_gallery/lib/demo/grid_list_demo.dart

@@ -133,7 +133,8 @@ class GridListDemo extends StatefulWidget {
 }
 
 class GridListDemoState extends State<GridListDemo> {
-  GridDemoTileStyle tileStyle = GridDemoTileStyle.twoLine;
+  static final GlobalKey<ScrollableState> _scrollableKey = new GlobalKey<ScrollableState>();
+  GridDemoTileStyle _tileStyle = GridDemoTileStyle.twoLine;
 
   List<Photo> photos = <Photo>[
     new Photo(
@@ -200,7 +201,7 @@ class GridListDemoState extends State<GridListDemo> {
 
   void changeTileStyle(GridDemoTileStyle value) {
     setState(() {
-      tileStyle = value;
+      _tileStyle = value;
     });
   }
 
@@ -211,6 +212,7 @@ class GridListDemoState extends State<GridListDemo> {
   Widget build(BuildContext context) {
     final Orientation orientation = MediaQuery.of(context).orientation;
     return new Scaffold(
+      scrollableKey: _scrollableKey,
       appBar: new AppBar(
         title: new Text('Grid list'),
         actions: <Widget>[
@@ -237,6 +239,7 @@ class GridListDemoState extends State<GridListDemo> {
         children: <Widget>[
           new Flexible(
             child: new ScrollableGrid(
+              scrollableKey: _scrollableKey,
               delegate: new FixedColumnCountGridDelegate(
                 columnCount: (orientation == Orientation.portrait) ? 2 : 3,
                 rowSpacing: 4.0,
@@ -247,7 +250,7 @@ class GridListDemoState extends State<GridListDemo> {
               children: photos.map((Photo photo) {
                 return new GridDemoPhotoItem(
                   photo: photo,
-                  tileStyle: tileStyle,
+                  tileStyle: _tileStyle,
                   onBannerTap: (Photo photo) {
                     setState(() {
                       photo.isFavorite = !photo.isFavorite;

examples/flutter_gallery/lib/demo/leave_behind_demo.dart

@@ -38,7 +38,8 @@ class LeaveBehindDemo extends StatefulWidget {
 }
 
 class LeaveBehindDemoState extends State<LeaveBehindDemo> {
-  final GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState>();
+  static final GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState>();
+  static final GlobalKey<ScrollableState> _scrollableKey = new GlobalKey<ScrollableState>();
   DismissDirection _dismissDirection = DismissDirection.horizontal;
   List<LeaveBehindItem> leaveBehindItems;
 
@@ -131,6 +132,7 @@ class LeaveBehindDemoState extends State<LeaveBehindDemo> {
   Widget build(BuildContext context) {
     return new Scaffold(
       key: _scaffoldKey,
+      scrollableKey: _scrollableKey,
       appBar: new AppBar(
         title: new Text('Swipe items to dismiss'),
         actions: <Widget>[
@@ -161,7 +163,10 @@ class LeaveBehindDemoState extends State<LeaveBehindDemo> {
           )
         ]
       ),
-      body: new Block(children: leaveBehindItems.map(buildItem).toList())
+      body: new Block(
+        scrollableKey: _scrollableKey,
+        children: leaveBehindItems.map(buildItem).toList()
+      )
     );
   }
 }

examples/flutter_gallery/lib/demo/list_demo.dart

@@ -14,7 +14,8 @@ class ListDemo extends StatefulWidget {
 }
 
 class ListDemoState extends State<ListDemo> {
-  final GlobalKey<ScaffoldState> scaffoldKey = new GlobalKey<ScaffoldState>();
+  static final GlobalKey<ScaffoldState> scaffoldKey = new GlobalKey<ScaffoldState>();
+  static final GlobalKey<ScrollableState> _scrollableKey = new GlobalKey<ScrollableState>();
 
   PersistentBottomSheetController<Null> _bottomSheet;
   MaterialListType _itemType = MaterialListType.threeLine;
@@ -171,6 +172,7 @@ class ListDemoState extends State<ListDemo> {
 
     return new Scaffold(
       key: scaffoldKey,
+      scrollableKey: _scrollableKey,
       appBar: new AppBar(
         title: new Text('Scrolling list\n$itemTypeText$layoutText'),
         actions: <Widget>[
@@ -193,6 +195,7 @@ class ListDemoState extends State<ListDemo> {
       ),
       body: new Scrollbar(
         child: new MaterialList(
+          scrollableKey: _scrollableKey,
           type: _itemType,
           padding: new EdgeInsets.symmetric(vertical: _dense ? 4.0 : 8.0),
           children: listItems

examples/flutter_gallery/lib/demo/overscroll_demo.dart

@@ -90,6 +90,7 @@ class OverscrollDemoState extends State<OverscrollDemo> {
 
     return new Scaffold(
       key: _scaffoldKey,
+      scrollableKey: _scrollableKey,
       appBar: new AppBar(
         title: new Text('$indicatorTypeText'),
         actions: <Widget>[

examples/flutter_gallery/lib/demo/pesto_demo.dart

@@ -51,6 +51,8 @@ class PestoDemo extends StatefulWidget {
 
 class _PestoDemoState extends State<PestoDemo> {
   final GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState>();
+  static final GlobalKey<ScrollableState> _homeScrollableKey = new GlobalKey<ScrollableState>();
+  static final GlobalKey<ScrollableState> _favoritesScrollableKey = new GlobalKey<ScrollableState>();
   final TextStyle favoritesMessageStyle = _textStyle(16.0);
   final TextStyle userStyle = _textStyle(12.0, FontWeight.bold);
   final TextStyle emailStyle = _textStyle(12.0).copyWith(color: Colors.black54);
@@ -61,6 +63,7 @@ class _PestoDemoState extends State<PestoDemo> {
       data: _kTheme,
       child: new Scaffold(
         key: _scaffoldKey,
+        scrollableKey: config.showFavorites ? _favoritesScrollableKey : _homeScrollableKey,
         appBarBehavior: AppBarBehavior.under,
         appBar: _buildAppBar(context),
         drawer: _buildDrawer(context),
@@ -180,6 +183,7 @@ class _PestoDemoState extends State<PestoDemo> {
     }
 
     return new ScrollableGrid(
+      scrollableKey: config.showFavorites ? _favoritesScrollableKey : _homeScrollableKey,
       delegate: new MaxTileWidthGridDelegate(
         maxTileWidth: 500.0,
         rowSpacing: 8.0,
@@ -282,7 +286,8 @@ class _RecipePage extends StatefulWidget {
 }
 
 class _RecipePageState extends State<_RecipePage> {
-  static final GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState>();
+  final GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState>();
+  final GlobalKey<ScrollableState> _scrollableKey = new GlobalKey<ScrollableState>();
   final TextStyle menuItemStyle = _textStyle(15.0).copyWith(color: Colors.black54, height: 24.0/15.0);
 
   double _getAppBarHeight(BuildContext context) => MediaQuery.of(context).size.height * 0.3;
@@ -291,6 +296,7 @@ class _RecipePageState extends State<_RecipePage> {
   Widget build(BuildContext context) {
     return new Scaffold(
       key: _scaffoldKey,
+      scrollableKey: _scrollableKey,
       appBarBehavior: AppBarBehavior.scroll,
       appBar: new AppBar(
         expandedHeight: _getAppBarHeight(context),
@@ -347,6 +353,7 @@ class _RecipePageState extends State<_RecipePage> {
         new ClampOverscrolls(
           value: true,
           child: new ScrollableViewport(
+            scrollableKey: _scrollableKey,
             child: new RepaintBoundary(
               child: new Padding(
                 padding: new EdgeInsets.only(top: appBarHeight),

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

@@ -293,6 +293,7 @@ class ShrineHome extends StatefulWidget {
 
 class _ShrineHomeState extends State<ShrineHome> {
   static final GlobalKey<ScaffoldState> scaffoldKey = new GlobalKey<ScaffoldState>(debugLabel: 'Order page');
+  static final GlobalKey<ScrollableState> scrollableKey = new GlobalKey<ScrollableState>();
   static final GridDelegate gridDelegate = new ShrineGridDelegate();
 
   void handleCompletedOrder(Order completedOrder) {
@@ -323,9 +324,11 @@ class _ShrineHomeState extends State<ShrineHome> {
     final Product featured = _products.firstWhere((Product product) => product.featureDescription != null);
     return new ShrinePage(
       scaffoldKey: scaffoldKey,
+      scrollableKey: scrollableKey,
       products: _products,
       shoppingCart: _shoppingCart,
       body: new ScrollableViewport(
+        scrollableKey: scrollableKey,
         child: new RepaintBoundary(
           child: new Column(
             children: <Widget>[

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

@@ -137,6 +137,7 @@ class OrderPage extends StatefulWidget {
 /// order to the shopping cart.
 class _OrderPageState extends State<OrderPage> {
   static final GlobalKey<ScaffoldState> scaffoldKey = new GlobalKey<ScaffoldState>(debugLabel: 'Order page');
+  static final GlobalKey<ScrollableState> scrollableKey = new GlobalKey<ScrollableState>();
 
   Order get currentOrder => ShrineOrderRoute.of(context).order;
 
@@ -162,6 +163,7 @@ class _OrderPageState extends State<OrderPage> {
   Widget build(BuildContext context) {
     return new ShrinePage(
       scaffoldKey: scaffoldKey,
+      scrollableKey: scrollableKey,
       products: config.products,
       shoppingCart: config.shoppingCart,
       floatingActionButton: new FloatingActionButton(
@@ -180,6 +182,7 @@ class _OrderPageState extends State<OrderPage> {
         )
       ),
       body: new Block(
+        scrollableKey: scrollableKey,
         children: <Widget>[
           new OrderItem(
             product: config.order.product,

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

@@ -17,6 +17,7 @@ class ShrinePage extends StatefulWidget {
   ShrinePage({
     Key key,
     this.scaffoldKey,
+    this.scrollableKey,
     this.body,
     this.floatingActionButton,
     this.products,
@@ -27,6 +28,7 @@ class ShrinePage extends StatefulWidget {
   }
 
   final GlobalKey<ScaffoldState> scaffoldKey;
+  final GlobalKey<ScrollableState> scrollableKey;
   final Widget body;
   final Widget floatingActionButton;
   final List<Product> products;
@@ -86,6 +88,7 @@ class ShrinePageState extends State<ShrinePage> {
     final ShrineTheme theme = ShrineTheme.of(context);
     return new Scaffold(
       key: config.scaffoldKey,
+      scrollableKey: config.scrollableKey,
       appBar: new AppBar(
         elevation: _appBarElevation,
         backgroundColor: theme.appBarBackgroundColor,

examples/flutter_gallery/lib/demo/tabs_demo.dart

@@ -9,6 +9,7 @@ import 'package:flutter/material.dart';
 
 class _Page {
   _Page({ this.label });
+  final GlobalKey<ScrollableState> scrollableKey = new GlobalKey<ScrollableState>();
   final String label;
   String get id => label[0];
 }
@@ -111,14 +112,35 @@ class _CardDataItem extends StatelessWidget {
   }
 }
 
-class TabsDemo extends StatelessWidget {
+class TabsDemo extends StatefulWidget {
+  TabsDemo({ Key key }) : super(key: key);
+
   static const String routeName = '/tabs';
 
+  @override
+  _TabsDemoState createState() => new _TabsDemoState();
+}
+
+class _TabsDemoState extends State<TabsDemo> {
+  _Page _selectedPage;
+
+  @override
+  void initState() {
+    super.initState();
+    _selectedPage = _allPages.keys.first;
+  }
+
   @override
   Widget build(BuildContext context) {
     return new TabBarSelection<_Page>(
       values: _allPages.keys.toList(),
+      onChanged: (_Page value) {
+        setState(() {
+          _selectedPage = value;
+       });
+      },
       child: new Scaffold(
+        scrollableKey: _selectedPage.scrollableKey,
         appBar: new AppBar(
           title: new Text('Tabs and scrolling'),
           bottom: new TabBar<_Page>(
@@ -130,6 +152,7 @@ class TabsDemo extends StatelessWidget {
         body: new TabBarView<_Page>(
           children: _allPages.keys.map((_Page page) {
             return new ScrollableList(
+              scrollableKey: _selectedPage.scrollableKey,
               padding: const EdgeInsets.symmetric(vertical: 8.0, horizontal: 16.0),
               itemExtent: _CardDataItem.height,
               children: _allPages[page].map((_CardData data) {

examples/flutter_gallery/lib/gallery/home.dart

@@ -97,7 +97,8 @@ class GalleryHome extends StatefulWidget {
 }
 
 class GalleryHomeState extends State<GalleryHome> {
-  final Key _homeKey = new ValueKey<String>("Gallery Home");
+  static final Key _homeKey = new ValueKey<String>("Gallery Home");
+  static final GlobalKey<ScrollableState> _scrollableKey = new GlobalKey<ScrollableState>();
   final List<Widget> _listItems = <Widget>[];
 
   @override
@@ -135,6 +136,7 @@ class GalleryHomeState extends State<GalleryHome> {
   Widget build(BuildContext context) {
     return new Scaffold(
       key: _homeKey,
+      scrollableKey: _scrollableKey,
       drawer: new GalleryDrawer(
         useLightTheme: config.useLightTheme,
         onThemeChanged: config.onThemeChanged,
@@ -157,7 +159,10 @@ class GalleryHomeState extends State<GalleryHome> {
         )
       ),
       appBarBehavior: AppBarBehavior.under,
-      body: new Block(children: _listItems)
+      body: new Block(
+       scrollableKey: _scrollableKey,
+       children: _listItems
+      )
     );
   }
 }

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

@@ -16,6 +16,7 @@ import 'icon_button.dart';
 import 'icons.dart';
 import 'material.dart';
 import 'snack_bar.dart';
+import 'theme.dart';
 
 const double _kFloatingActionButtonMargin = 16.0; // TODO(hmuller): should be device dependent
 const Duration _kFloatingActionButtonSegue = const Duration(milliseconds: 200);
@@ -52,12 +53,18 @@ enum _ScaffoldSlot {
   snackBar,
   floatingActionButton,
   drawer,
+  statusBar,
 }
 
 class _ScaffoldLayout extends MultiChildLayoutDelegate {
-  _ScaffoldLayout({ this.padding, this.appBarBehavior: AppBarBehavior.anchor });
+  _ScaffoldLayout({
+    this.padding,
+    this.statusBarHeight,
+    this.appBarBehavior: AppBarBehavior.anchor
+  });
 
   final EdgeInsets padding;
+  final double statusBarHeight;
   final AppBarBehavior appBarBehavior;
 
   @override
@@ -120,6 +127,11 @@ class _ScaffoldLayout extends MultiChildLayoutDelegate {
       positionChild(_ScaffoldSlot.floatingActionButton, new Offset(fabX, fabY));
     }
 
+    if (hasChild(_ScaffoldSlot.statusBar)) {
+      layoutChild(_ScaffoldSlot.statusBar, fullWidthConstraints.tighten(height: statusBarHeight));
+      positionChild(_ScaffoldSlot.statusBar, Offset.zero);
+    }
+
     if (hasChild(_ScaffoldSlot.drawer)) {
       layoutChild(_ScaffoldSlot.drawer, new BoxConstraints.tight(size));
       positionChild(_ScaffoldSlot.drawer, Offset.zero);
@@ -270,9 +282,7 @@ class Scaffold extends StatefulWidget {
     this.scrollableKey,
     this.appBarBehavior: AppBarBehavior.anchor,
     this.resizeToAvoidBottomPadding: true
-  }) : super(key: key) {
-    assert(scrollableKey != null ? (appBarBehavior != AppBarBehavior.anchor) : true);
-  }
+  }) : super(key: key);
 
   /// An app bar to display at the top of the scaffold.
   final AppBar appBar;
@@ -298,7 +308,7 @@ class Scaffold extends StatefulWidget {
   ///
   /// Used to control scroll-linked effects, such as the collapse of the
   /// [appBar].
-  final Key scrollableKey;
+  final GlobalKey<ScrollableState> scrollableKey;
 
   /// How the [appBar] should respond to scrolling.
   ///
@@ -663,6 +673,19 @@ class ScaffoldState extends State<Scaffold> {
     return appBar;
   }
 
+  // On iOS, tapping the status bar scrolls the app's primary scrollable to the top.
+  void _handleStatusBarTap() {
+    ScrollableState scrollable = config.scrollableKey?.currentState;
+    if (scrollable == null || scrollable.scrollBehavior is! ExtentScrollBehavior)
+      return;
+
+    ExtentScrollBehavior behavior = scrollable.scrollBehavior;
+    scrollable.scrollTo(
+      behavior.minScrollOffset,
+      duration: const Duration(milliseconds: 300)
+    );
+  }
+
   @override
   Widget build(BuildContext context) {
     EdgeInsets padding = MediaQuery.of(context).padding;
@@ -729,6 +752,16 @@ class ScaffoldState extends State<Scaffold> {
       )
     ));
 
+    if (Theme.of(context).platform == TargetPlatform.iOS) {
+      children.add(new LayoutId(
+        id: _ScaffoldSlot.statusBar,
+        child: new GestureDetector(
+          behavior: HitTestBehavior.opaque,
+          onTap: _handleStatusBarTap
+        )
+      ));
+    }
+
     if (config.drawer != null) {
       children.add(new LayoutId(
         id: _ScaffoldSlot.drawer,
@@ -739,12 +772,12 @@ class ScaffoldState extends State<Scaffold> {
       ));
     }
 
-    EdgeInsets appPadding = (config.appBarBehavior != AppBarBehavior.anchor) ?
-        EdgeInsets.zero : padding;
+    EdgeInsets appPadding = (config.appBarBehavior != AppBarBehavior.anchor) ? EdgeInsets.zero : padding;
     Widget application = new CustomMultiChildLayout(
       children: children,
       delegate: new _ScaffoldLayout(
         padding: appPadding,
+        statusBarHeight: padding.top,
         appBarBehavior: config.appBarBehavior
       )
     );

packages/flutter/test/material/scaffold_test.dart

@@ -128,4 +128,72 @@ void main() {
     RenderBox renderBox = tester.renderObject(find.byKey(appBarKey));
     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: new 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('$index'))
+              )
+            )
+          )
+        )
+      )
+    );
+
+    expect(scrollableKey.currentState.scrollOffset, equals(500.0));
+    await tester.tapAt(const Point(100.0, 10.0));
+    await tester.pump();
+    await tester.pump(new Duration(seconds: 1));
+    expect(scrollableKey.currentState.scrollOffset, equals(0.0));
+  });
+
+  testWidgets('Tapping the status bar does not scroll to top on Android', (WidgetTester tester) async {
+    final GlobalKey<ScrollableState> scrollableKey = new GlobalKey<ScrollableState>();
+    final Key appBarKey = new UniqueKey();
+
+    await tester.pumpWidget(
+      new MaterialApp(
+        theme: new ThemeData(platform: TargetPlatform.android),
+        home: new MediaQuery(
+          data: new MediaQueryData(padding: const EdgeInsets.only(top: 25.0)), // status bar
+          child: new Scaffold(
+            scrollableKey: scrollableKey,
+            appBar: new AppBar(
+              key: appBarKey,
+              title: new Text('Title')
+            ),
+            body: new Block(
+              scrollableKey: scrollableKey,
+              initialScrollOffset: 500.0,
+              children: new List<Widget>.generate(20,
+                (int index) => new SizedBox(height: 100.0, child: new Text('$index'))
+              )
+            )
+          )
+        )
+      )
+    );
+
+    expect(scrollableKey.currentState.scrollOffset, equals(500.0));
+    await tester.tapAt(const Point(100.0, 10.0));
+    await tester.pump();
+    await tester.pump(new Duration(seconds: 1));
+    expect(scrollableKey.currentState.scrollOffset, equals(500.0));
+  });
 }