Merge pull request #878 from HansMuller/pageable_list_tabs

TabBarView is-a PageableList, doesn't need itemExtent

Base TabBarView on PageableList so that itemExtent and its SizeObserver aren't needed.

TabBarView scrolling is still TBD.

examples/material_gallery/lib/demo/tabs_demo.dart

@@ -22,31 +22,19 @@ class TabsDemo extends StatefulComponent {
 }
 
 class _TabsDemoState extends State<TabsDemo> {
-  double _viewWidth = 100.0;
-
-  void _handleSizeChanged(Size newSize) {
-    setState(() {
-      _viewWidth = newSize.width;
-    });
-  }
-
   Widget build(_) {
-    return new SizeObserver(
-      onSizeChanged: _handleSizeChanged,
-      child: new TabBarView<String>(
-        selection: _selection,
-        items: _iconNames,
-        itemExtent: _viewWidth,
-        itemBuilder: (BuildContext context, String iconName, int index) {
-          return new Container(
-            key: new ValueKey<String>(iconName),
-            padding: const EdgeDims.all(12.0),
-            child: new Card(
-              child: new Center(child: new Icon(icon: "action/$iconName", size:IconSize.s48))
-            )
-          );
-        }
-      )
+    return new TabBarView<String>(
+      selection: _selection,
+      items: _iconNames,
+      itemBuilder: (BuildContext context, String iconName, int index) {
+        return new Container(
+          key: new ValueKey<String>(iconName),
+          padding: const EdgeDims.all(12.0),
+          child: new Card(
+            child: new Center(child: new Icon(icon: "action/$iconName", size:IconSize.s48))
+          )
+        );
+      }
     );
   }
 }

examples/stocks/lib/stock_home.dart

@@ -272,36 +272,25 @@ class StockHomeState extends State<StockHome> {
     );
   }
 
-  double _viewWidth = 100.0;
-  void _handleSizeChanged(Size newSize) {
-    setState(() {
-      _viewWidth = newSize.width;
-    });
-  }
-
   Widget build(BuildContext context) {
     return new Scaffold(
       key: _scaffoldKey,
       toolBar: _isSearching ? buildSearchBar() : buildToolBar(),
       floatingActionButton: buildFloatingActionButton(),
       drawer: _buildDrawer(context),
-      body: new SizeObserver(
-        onSizeChanged: _handleSizeChanged,
-        child: new TabBarView<StockHomeTab>(
-          selection: _tabBarSelection,
-          items: <StockHomeTab>[StockHomeTab.market, StockHomeTab.portfolio],
-          itemExtent: _viewWidth,
-          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);
-            }
+      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);
           }
-        )
+        }
       )
     );
   }

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

@@ -28,7 +28,7 @@ const double _kMinTabWidth = 72.0;
 const double _kMaxTabWidth = 264.0;
 const EdgeDims _kTabLabelPadding = const EdgeDims.symmetric(horizontal: 12.0);
 const double _kTabBarScrollDrag = 0.025;
-const Duration _kTabBarScroll = const Duration(milliseconds: 200);
+const Duration _kTabBarScroll = const Duration(milliseconds: 300);
 
 class _TabBarParentData extends ContainerBoxParentDataMixin<RenderBox> { }
 
@@ -612,19 +612,17 @@ class _TabBarState extends ScrollableState<TabBar> {
   }
 }
 
-class TabBarView<T> extends ScrollableList<T> {
+class TabBarView<T> extends PageableList<T> {
   TabBarView({
     Key key,
     this.selection,
     List<T> items,
-    ItemBuilder<T> itemBuilder,
-    double itemExtent
+    ItemBuilder<T> itemBuilder
   }) : super(
     key: key,
     scrollDirection: ScrollDirection.horizontal,
     items: items,
     itemBuilder: itemBuilder,
-    itemExtent: itemExtent,
     itemsWrap: false
   ) {
     assert(selection != null);
@@ -640,9 +638,11 @@ class _NotScrollable extends BoundedBehavior {
   bool get isScrollable => false;
 }
 
-class _TabBarViewState<T> extends ScrollableListState<T, TabBarView<T>> {
+class _TabBarViewState<T> extends PageableListState<T, TabBarView<T>> {
 
-  ScrollBehavior createScrollBehavior() => new _NotScrollable();
+  final _NotScrollable _notScrollable = new _NotScrollable();
+  ScrollBehavior createScrollBehavior() => _notScrollable;
+  ExtentScrollBehavior get scrollBehavior => _notScrollable;
 
   List<int> _itemIndices = [0, 1];
   AnimationDirection _scrollDirection = AnimationDirection.forward;
@@ -655,10 +655,10 @@ class _TabBarViewState<T> extends ScrollableListState<T, TabBarView<T>> {
       scrollTo(0.0);
     } else if (selectedIndex == config.items.length - 1) {
       _itemIndices = <int>[selectedIndex - 1, selectedIndex];
-      scrollTo(config.itemExtent);
+      scrollTo(1.0);
     } else {
       _itemIndices = <int>[selectedIndex - 1, selectedIndex, selectedIndex + 1];
-      scrollTo(config.itemExtent);
+      scrollTo(1.0);
     }
   }
 
@@ -680,12 +680,6 @@ class _TabBarViewState<T> extends ScrollableListState<T, TabBarView<T>> {
     super.dispose();
   }
 
-  void didUpdateConfig(TabBarView oldConfig) {
-    super.didUpdateConfig(oldConfig);
-    if (oldConfig.itemExtent != config.itemExtent && !_performance.isAnimating)
-      _initItemIndicesAndScrollPosition();
-  }
-
   void _handleStatusChange(PerformanceStatus status) {
     final int selectedIndex = config.selection.index;
     final int previousSelectedIndex = config.selection.previousIndex;
@@ -705,9 +699,9 @@ class _TabBarViewState<T> extends ScrollableListState<T, TabBarView<T>> {
 
   void _handleProgressChange() {
     if (_scrollDirection == AnimationDirection.forward)
-      scrollTo(config.itemExtent * _performance.progress);
+      scrollTo(_performance.progress);
     else
-      scrollTo(config.itemExtent * (1.0 - _performance.progress));
+      scrollTo(1.0 - _performance.progress);
   }
 
   int get itemCount => _itemIndices.length;