TabBarSelection is now expected to be an ancestor of its TabBar and TabBarView.

examples/material_gallery/lib/demo/tabs_demo.dart

@@ -7,11 +7,16 @@ import 'package:flutter/material.dart';
 import 'widget_demo.dart';
 
 final List<String> _iconNames = <String>["event", "home", "android", "alarm", "face", "language"];
-final TabBarSelection _selection = new TabBarSelection(maxIndex: _iconNames.length - 1);
 
-Widget buildTabBar(_) {
+Widget _buildTabBarSelection(_, Widget child) {
+  return new TabBarSelection(
+    maxIndex: _iconNames.length - 1,
+    child: child
+  );
+}
+
+Widget _buildTabBar(_) {
   return new TabBar(
-    selection: _selection,
     isScrollable: true,
     labels: _iconNames.map((String iconName) => new TabLabel(text: iconName, icon: "action/$iconName")).toList()
   );
@@ -24,7 +29,6 @@ class TabsDemo extends StatefulComponent {
 class _TabsDemoState extends State<TabsDemo> {
   Widget build(_) {
     return new TabBarView<String>(
-      selection: _selection,
       items: _iconNames,
       itemBuilder: (BuildContext context, String iconName, int index) {
         return new Container(
@@ -42,6 +46,7 @@ class _TabsDemoState extends State<TabsDemo> {
 final WidgetDemo kTabsDemo = new WidgetDemo(
   title: 'Tabs',
   routeName: '/tabs',
-  tabBarBuilder: buildTabBar,
+  tabBarBuilder: _buildTabBar,
+  pageWrapperBuilder: _buildTabBarSelection,
   builder: (_) => new TabsDemo()
 );

examples/material_gallery/lib/demo/widget_demo.dart

@@ -4,12 +4,22 @@
 
 import 'package:flutter/material.dart';
 
+typedef Widget PageWrapperBuilder(BuildContext context, Widget child);
+
 class WidgetDemo {
-  WidgetDemo({ this.title, this.routeName, this.tabBarBuilder, this.floatingActionButtonBuilder, this.builder });
+  WidgetDemo({
+    this.title,
+    this.routeName,
+    this.tabBarBuilder,
+    this.pageWrapperBuilder,
+    this.floatingActionButtonBuilder,
+    this.builder
+  });
 
   final String title;
   final String routeName;
   final WidgetBuilder tabBarBuilder;
+  final PageWrapperBuilder pageWrapperBuilder;
   final WidgetBuilder floatingActionButtonBuilder;
   final WidgetBuilder builder;
 }

examples/material_gallery/lib/gallery_page.dart

@@ -63,20 +63,27 @@ class _GalleryPageState extends State<GalleryPage> {
     return builder != null ? builder(context) : null;
   }
 
+  Widget _buildPageWrapper(BuildContext context, Widget child) {
+    final PageWrapperBuilder builder = config.active?.pageWrapperBuilder;
+    return builder != null ? builder(context, child) : child;
+  }
+
   Widget _buildFloatingActionButton() {
     final WidgetBuilder builder = config.active?.floatingActionButtonBuilder;
     return builder != null ? builder(context) : null;
   }
 
   Widget build(BuildContext context) {
-    return new Scaffold(
-      toolBar: new ToolBar(
-        center: new Text(config.active?.title ?? 'Flutter Material gallery'),
-        tabBar: _buildTabBar()
-      ),
-      drawer: _buildDrawer(),
-      floatingActionButton: _buildFloatingActionButton(),
-      body: _buildBody()
+    return _buildPageWrapper(context,
+      new Scaffold(
+        toolBar: new ToolBar(
+          center: new Text(config.active?.title ?? 'Flutter Material gallery'),
+          tabBar: _buildTabBar()
+        ),
+        drawer: _buildDrawer(),
+        floatingActionButton: _buildFloatingActionButton(),
+        body: _buildBody()
+      )
     );
   }
 }

examples/stocks/lib/stock_home.dart

@@ -24,15 +24,9 @@ class StockHomeState extends State<StockHome> {
   final GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState>();
   bool _isSearching = false;
   String _searchQuery;
-  TabBarSelection _tabBarSelection;
 
   void initState() {
     super.initState();
-    _tabBarSelection = PageStorage.of(context)?.readState(context);
-    if (_tabBarSelection == null) {
-      _tabBarSelection = new TabBarSelection(maxIndex: 1);
-      PageStorage.of(context)?.writeState(context, _tabBarSelection);
-    }
   }
 
   void _handleSearchBegin() {
@@ -168,7 +162,6 @@ class StockHomeState extends State<StockHome> {
         )
       ],
       tabBar: new TabBar(
-        selection: _tabBarSelection,
         labels: <TabLabel>[
           new TabLabel(text: StockStrings.of(context).market()),
           new TabLabel(text: StockStrings.of(context).portfolio())
@@ -273,24 +266,26 @@ class StockHomeState extends State<StockHome> {
   }
 
   Widget build(BuildContext context) {
-    return new Scaffold(
-      key: _scaffoldKey,
-      toolBar: _isSearching ? buildSearchBar() : buildToolBar(),
-      floatingActionButton: buildFloatingActionButton(),
-      drawer: _buildDrawer(context),
-      body: new TabBarView<StockHomeTab>(
-        selection: _tabBarSelection,
-        items: <StockHomeTab>[StockHomeTab.market, StockHomeTab.portfolio],
-        itemBuilder: (BuildContext context, StockHomeTab tab, _) {
-          switch (tab) {
-            case StockHomeTab.market:
-              return _buildStockTab(context, tab, config.symbols);
-            case StockHomeTab.portfolio:
-              return _buildStockTab(context, tab, portfolioSymbols);
-            default:
-              assert(false);
+    return new TabBarSelection(
+      maxIndex: 1,
+      child: new Scaffold(
+        key: _scaffoldKey,
+        toolBar: _isSearching ? buildSearchBar() : buildToolBar(),
+        floatingActionButton: buildFloatingActionButton(),
+        drawer: _buildDrawer(context),
+        body: new TabBarView<StockHomeTab>(
+          items: <StockHomeTab>[StockHomeTab.market, StockHomeTab.portfolio],
+          itemBuilder: (BuildContext context, StockHomeTab tab, _) {
+            switch (tab) {
+              case StockHomeTab.market:
+                return _buildStockTab(context, tab, config.symbols);
+              case StockHomeTab.portfolio:
+                return _buildStockTab(context, tab, portfolioSymbols);
+              default:
+                assert(false);
+            }
           }
-        }
+        )
       )
     );
   }

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

@@ -381,32 +381,26 @@ class _TabsScrollBehavior extends BoundedBehavior {
   }
 }
 
-class _TabBarSelection extends InheritedWidget {
-  _TabBarSelection({
-    this.selection,
-    Key key,
-    Widget child
-  }) : super(key: key, child: child);
-
-  final TabBarSelectionState selection;
-
-  bool updateShouldNotify(_TabBarSelection oldWidget) => selection != oldWidget.selection;
+abstract class TabBarSelectionPerformanceListener {
+  void handleStatusChange(PerformanceStatus status);
+  void handleProgressChange();
+  void handleSelectionDeactivate();
 }
 
 class TabBarSelection extends StatefulComponent {
   TabBarSelection({
     Key key,
-    this.index: 0,
+    this.index,
     this.maxIndex,
     this.onChanged,
-    Widget this.child
-  }) {
+    this.child
+  }) : super(key: key)  {
+    assert(child != null);
     assert(maxIndex != null);
-    assert(index != null);
-    assert(index >= 0 && index <= maxIndex);
+    assert((index != null) ? index >= 0 && index <= maxIndex : true);
   }
 
-  final int index;  // TBD: this doesn't work yet...
+  final int index;
   final int maxIndex;
   final Widget child;
   final ValueChanged<int> onChanged;
@@ -414,20 +408,25 @@ class TabBarSelection extends StatefulComponent {
   TabBarSelectionState createState() => new TabBarSelectionState();
 
   static TabBarSelectionState of(BuildContext context) {
-    _TabBarSelection widget = context.inheritFromWidgetOfType(_TabBarSelection);
-    return widget?.selection;
+    return context.ancestorStateOfType(TabBarSelectionState);
   }
 }
 
 class TabBarSelectionState extends State<TabBarSelection> {
 
+  PerformanceView get performance => _performance.view;
   // Both the TabBar and TabBarView classes access _performance because they
   // alternately drive selection progress between tabs.
-  PerformanceView get performance => _performance.view;
   final _performance = new Performance(duration: _kTabBarScroll, progress: 1.0);
 
+  void initState() {
+    super.initState();
+    _index = config.index ?? PageStorage.of(context)?.readState(context) ?? 0;
+  }
+
   void dispose() {
     _performance.stop();
+    PageStorage.of(context)?.writeState(context, _index);
     super.dispose();
   }
 
@@ -435,11 +434,12 @@ class TabBarSelectionState extends State<TabBarSelection> {
   bool get indexIsChanging => _indexIsChanging;
 
   int get index => _index;
-  int _index = 0;
+  int _index;
   void set index(int value) {
     if (value == _index)
       return;
-    _previousIndex = _index;
+    if (!_indexIsChanging)
+      _previousIndex = _index;
     _index = value;
     _indexIsChanging = true;
 
@@ -469,17 +469,43 @@ class TabBarSelectionState extends State<TabBarSelection> {
     _performance
       ..progress = progress
       ..forward().then((_) {
-        if (config.onChanged != null)
-          config.onChanged(_index);
-        _indexIsChanging = false;
+        if (_performance.progress == 1.0) {
+          if (config.onChanged != null)
+            config.onChanged(_index);
+          _indexIsChanging = false;
+        }
       });
   }
 
   int get previousIndex => _previousIndex;
   int _previousIndex = 0;
 
+  final List<TabBarSelectionPerformanceListener> _performanceListeners = <TabBarSelectionPerformanceListener>[];
+
+  void registerPerformanceListener(TabBarSelectionPerformanceListener listener) {
+    _performanceListeners.add(listener);
+    _performance
+      ..addStatusListener(listener.handleStatusChange)
+      ..addListener(listener.handleProgressChange);
+  }
+
+  void unregisterPerformanceListener(TabBarSelectionPerformanceListener listener) {
+    _performanceListeners.remove(listener);
+    _performance
+      ..removeStatusListener(listener.handleStatusChange)
+      ..removeListener(listener.handleProgressChange);
+  }
+
+  void deactivate() {
+    for (TabBarSelectionPerformanceListener listener in _performanceListeners.toList()) {
+      listener.handleSelectionDeactivate();
+      unregisterPerformanceListener(listener);
+    }
+    assert(_performanceListeners.isEmpty);
+  }
+
   Widget build(BuildContext context) {
-    return new _TabBarSelection(selection: this, child: config.child);
+    return config.child;
   }
 }
 
@@ -507,40 +533,30 @@ class TabBar extends Scrollable {
   _TabBarState createState() => new _TabBarState();
 }
 
-class _TabBarState extends ScrollableState<TabBar> {
+class _TabBarState extends ScrollableState<TabBar> implements TabBarSelectionPerformanceListener {
 
   TabBarSelectionState _selection;
   bool _indexIsChanging = false;
 
   int get _tabCount => config.labels.length;
 
-  void _addSelectionListeners(TabBarSelectionState selection) {
-    if (selection != null) {
-      selection._performance
-        ..addStatusListener(_handleStatusChange)
-        ..addListener(_handleProgressChange);
-    }
-  }
-
-  void _removeSelectionListeners(TabBarSelectionState selection) {
-    if (selection != null) {
-      selection._performance
-        ..removeStatusListener(_handleStatusChange)
-        ..removeListener(_handleProgressChange);
-    }
-  }
-
   void initState() {
     super.initState();
     scrollBehavior.isScrollable = config.isScrollable;
+    _selection = TabBarSelection.of(context);
+    _selection?.registerPerformanceListener(this);
   }
 
   void dispose() {
-    _removeSelectionListeners(_selection);
+    _selection?.unregisterPerformanceListener(this);
     super.dispose();
   }
 
-  void _handleStatusChange(PerformanceStatus status) {
+  void handleSelectionDeactivate() {
+    _selection = null;
+  }
+
+  void handleStatusChange(PerformanceStatus status) {
     if (_tabCount == 0)
       return;
 
@@ -561,7 +577,7 @@ class _TabBarState extends ScrollableState<TabBar> {
     }
   }
 
-  void _handleProgressChange() {
+  void handleProgressChange() {
     if (_tabCount == 0 || _selection == null)
       return;
 
@@ -574,9 +590,11 @@ class _TabBarState extends ScrollableState<TabBar> {
         ..curve = Curves.ease;
       _indexIsChanging = true;
     }
-    setState(() {
-      _indicatorRect.setProgress(_selection.performance.progress, AnimationDirection.forward);
-    });
+    Rect oldRect = _indicatorRect.value;
+    _indicatorRect.setProgress(_selection.performance.progress, AnimationDirection.forward);
+    Rect newRect = _indicatorRect.value;
+    if (oldRect != newRect)
+      setState(() { });
   }
 
   Size _viewportSize = Size.zero;
@@ -671,8 +689,8 @@ class _TabBarState extends ScrollableState<TabBar> {
     TabBarSelectionState oldSelection = _selection;
     _selection = TabBarSelection.of(context);
     if (oldSelection != _selection) {
-      _removeSelectionListeners(oldSelection);
-      _addSelectionListeners(_selection);
+      oldSelection?.registerPerformanceListener(this);
+      _selection?.registerPerformanceListener(this);
     }
 
     assert(config.labels != null && config.labels.isNotEmpty);
@@ -746,7 +764,7 @@ class TabBarView<T> extends PageableList<T> {
   _TabBarViewState createState() => new _TabBarViewState<T>();
 }
 
-class _TabBarViewState<T> extends PageableListState<T, TabBarView<T>> {
+class _TabBarViewState<T> extends PageableListState<T, TabBarView<T>> implements TabBarSelectionPerformanceListener {
 
   TabBarSelectionState _selection;
   List<int> _itemIndices = [0, 1];
@@ -754,16 +772,6 @@ class _TabBarViewState<T> extends PageableListState<T, TabBarView<T>> {
 
   int get _tabCount => config.items.length;
 
-  void _addSelectionListeners(TabBarSelectionState selection) {
-    if (selection != null)
-      selection._performance.addListener(_handleProgressChange);
-  }
-
-  void _removeSelectionListeners(TabBarSelectionState selection) {
-    if (selection != null)
-      selection._performance.removeListener(_handleProgressChange);
-  }
-
   BoundedBehavior _boundedBehavior;
 
   ExtentScrollBehavior get scrollBehavior {
@@ -771,11 +779,25 @@ class _TabBarViewState<T> extends PageableListState<T, TabBarView<T>> {
     return _boundedBehavior;
   }
 
+
+  void initState() {
+    super.initState();
+    _selection = TabBarSelection.of(context);
+    if (_selection != null) {
+      _selection.registerPerformanceListener(this);
+      _initItemIndicesAndScrollPosition();
+    }
+  }
+
   void dispose() {
-    _removeSelectionListeners(_selection);
+    _selection?.unregisterPerformanceListener(this);
     super.dispose();
   }
 
+  void handleSelectionDeactivate() {
+    _selection = null;
+  }
+
   void _initItemIndicesAndScrollPosition() {
     assert(_selection != null);
     final int selectedIndex = _selection.index;
@@ -791,7 +813,10 @@ class _TabBarViewState<T> extends PageableListState<T, TabBarView<T>> {
     }
   }
 
-  void _handleProgressChange() {
+  void handleStatusChange(PerformanceStatus status) {
+  }
+
+  void handleProgressChange() {
     if (_selection == null || !_selection.indexIsChanging)
       return;
     // The TabBar is driving the TabBarSelection performance.
@@ -865,10 +890,8 @@ class _TabBarViewState<T> extends PageableListState<T, TabBarView<T>> {
     TabBarSelectionState oldSelection = _selection;
     _selection = TabBarSelection.of(context);
     if (oldSelection != _selection) {
-      _removeSelectionListeners(oldSelection);
-      _addSelectionListeners(_selection);
-      if (_selection != null)
-        _initItemIndicesAndScrollPosition();
+      oldSelection?.unregisterPerformanceListener(this);
+      _selection?.registerPerformanceListener(this);
     }
 
     return _itemIndices

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

@@ -8,7 +8,6 @@ import 'constants.dart';
 import 'icon_theme.dart';
 import 'icon_theme_data.dart';
 import 'material.dart';
-import 'tabs.dart';
 import 'theme.dart';
 import 'typography.dart';
 
@@ -30,7 +29,7 @@ class ToolBar extends StatelessComponent {
   final Widget center;
   final List<Widget> right;
   final Widget bottom;
-  final TabBar tabBar;
+  final Widget tabBar;
   final int elevation;
   final Color backgroundColor;
   final TextTheme textTheme;

packages/flutter/test/widget/tabs_test.dart

@@ -7,14 +7,15 @@ import 'package:flutter/material.dart';
 import 'package:flutter/widgets.dart';
 import 'package:test/test.dart';
 
-TabBarSelection selection;
-
 Widget buildFrame({ List<String> tabs, bool isScrollable: false }) {
   return new Material(
-    child: new TabBar(
-      labels: tabs.map((String tab) => new TabLabel(text: tab)).toList(),
-      selection: selection,
-      isScrollable: isScrollable
+    child: new TabBarSelection(
+      index: 2,
+      maxIndex: tabs.length - 1,
+      child: new TabBar(
+        labels: tabs.map((String tab) => new TabLabel(text: tab)).toList(),
+        isScrollable: isScrollable
+      )
     )
   );
 }
@@ -23,9 +24,10 @@ void main() {
   test('TabBar tap selects tab', () {
     testWidgets((WidgetTester tester) {
       List<String> tabs = <String>['A', 'B', 'C'];
-      selection = new TabBarSelection(index: 2, maxIndex: tabs.length - 1);
 
       tester.pumpWidget(buildFrame(tabs: tabs, isScrollable: false));
+      TabBarSelectionState selection = tester.findStateOfType(TabBarSelectionState);
+      expect(selection, isNotNull);
       expect(tester.findText('A'), isNotNull);
       expect(tester.findText('B'), isNotNull);
       expect(tester.findText('C'), isNotNull);
@@ -51,9 +53,10 @@ void main() {
   test('Scrollable TabBar tap selects tab', () {
     testWidgets((WidgetTester tester) {
       List<String> tabs = <String>['A', 'B', 'C'];
-      selection = new TabBarSelection(index: 2, maxIndex: tabs.length - 1);
 
       tester.pumpWidget(buildFrame(tabs: tabs, isScrollable: true));
+      TabBarSelectionState selection = tester.findStateOfType(TabBarSelectionState);
+      expect(selection, isNotNull);
       expect(tester.findText('A'), isNotNull);
       expect(tester.findText('B'), isNotNull);
       expect(tester.findText('C'), isNotNull);