Add ScrollController.initialScrollOffset (#7916)

Also, move the creation of the ScrollPosition to ScrollController.

Finally, remove TestScrollable in favor of CustomScrollView, which is the
production version of this widget.

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

@@ -10,6 +10,17 @@ import 'package:meta/meta.dart';
 import 'scroll_position.dart';
 
 class ScrollController {
+  ScrollController({
+    this.initialScrollOffset,
+  });
+
+  /// The initial value to use for [offset].
+  ///
+  /// If [initialScrollOffset] is non-null, new [ScrollPosition] objects that
+  /// are created and attached to this controller will have their offset
+  /// initialized to this value.
+  final double initialScrollOffset;
+
   final List<ScrollPosition> _positions = <ScrollPosition>[];
 
   double get offset {
@@ -87,4 +98,21 @@ class ScrollController {
     assert(_positions.contains(position));
     _positions.remove(position);
   }
+
+  static ScrollPosition createDefaultScrollPosition(ScrollPhysics physics, AbstractScrollState state, ScrollPosition oldPosition) {
+    return new ScrollPosition(
+      physics: physics,
+      state: state,
+      oldPosition: oldPosition,
+    );
+  }
+
+  ScrollPosition createScrollPosition(ScrollPhysics physics, AbstractScrollState state, ScrollPosition oldPosition) {
+    return new ScrollPosition(
+      physics: physics,
+      state: state,
+      offset: initialScrollOffset,
+      oldPosition: oldPosition,
+    );
+  }
 }

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

@@ -39,12 +39,6 @@ abstract class ScrollPhysics {
 
   ScrollPhysics applyTo(ScrollPhysics parent);
 
-  ScrollPosition createScrollPosition(ScrollPhysics physics, AbstractScrollState state, ScrollPosition oldPosition) {
-    if (parent == null)
-      return new ScrollPosition(physics, state, oldPosition);
-    return parent.createScrollPosition(physics, state, oldPosition);
-  }
-
   /// Used by [DragScrollActivity] and other user-driven activities to
   /// convert an offset in logical pixels as provided by the [DragUpdateDetails]
   /// into a delta to apply using [setPixels].
@@ -101,18 +95,6 @@ abstract class ScrollPhysics {
 
   Tolerance get tolerance => parent?.tolerance ?? _kDefaultTolerance;
 
-  @mustCallSuper
-  bool shouldUpdateScrollPosition(@checked ScrollPhysics other) {
-    if ((parent == null) != (other.parent == null))
-      return true;
-    if (parent == null) {
-      assert(other.parent == null);
-      return false;
-    }
-    return parent.runtimeType != other.parent.runtimeType
-        || parent.shouldUpdateScrollPosition(other.parent);
-  }
-
   @override
   String toString() {
     if (parent == null)
@@ -122,10 +104,16 @@ abstract class ScrollPhysics {
 }
 
 class ScrollPosition extends ViewportOffset {
-  ScrollPosition(this.physics, this.state, ScrollPosition oldPosition) {
+  ScrollPosition({
+    @required this.physics,
+    @required this.state,
+    double offset: 0.0,
+    ScrollPosition oldPosition,
+  }) : _pixels = offset ?? 0.0 {
     assert(physics != null);
     assert(state != null);
     assert(state.vsync != null);
+    assert(pixels != null);
     if (oldPosition != null)
       absorb(oldPosition);
     if (activity == null)
@@ -140,7 +128,7 @@ class ScrollPosition extends ViewportOffset {
 
   @override
   double get pixels => _pixels;
-  double _pixels = 0.0;
+  double _pixels;
 
   Future<Null> ensureVisible(RenderObject object, {
     double alignment: 0.0,

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

@@ -128,17 +128,20 @@ class Scrollable2State extends State<Scrollable2> with TickerProviderStateMixin
     ScrollPhysics physics = _configuration.getScrollPhysics(context);
     if (config.physics != null)
       physics = config.physics.applyTo(physics);
+    final ScrollController controller = config.controller;
     final ScrollPosition oldPosition = position;
     if (oldPosition != null) {
-      config.controller?.detach(oldPosition);
+      controller?.detach(oldPosition);
       // It's important that we not dispose the old position until after the
       // viewport has had a chance to unregister its listeners from the old
       // position. So, schedule a microtask to do it.
       scheduleMicrotask(oldPosition.dispose);
     }
-    _position = physics.createScrollPosition(physics, this, oldPosition);
+
+    _position = controller?.createScrollPosition(physics, this, oldPosition)
+      ?? ScrollController.createDefaultScrollPosition(physics, this, oldPosition);
     assert(position != null);
-    config.controller?.attach(position);
+    controller?.attach(position);
   }
 
   @override
@@ -148,12 +151,8 @@ class Scrollable2State extends State<Scrollable2> with TickerProviderStateMixin
   }
 
   bool _shouldUpdatePosition(Scrollable2 oldConfig) {
-    if (config.physics == oldConfig.physics)
-      return false;
-    if ((config.physics == null) != (oldConfig.physics == null))
-      return true;
-    return config.physics.runtimeType != oldConfig.physics.runtimeType
-        || config.physics.shouldUpdateScrollPosition(oldConfig.physics);
+    return config.physics?.runtimeType != oldConfig.physics?.runtimeType
+        || config.controller?.runtimeType != config.controller?.runtimeType;
   }
 
   @override

packages/flutter/test/widgets/block_test.dart

@@ -6,8 +6,6 @@ import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
 
-import 'test_widgets.dart';
-
 final Key blockKey = new Key('test');
 
 void main() {
@@ -132,7 +130,7 @@ void main() {
       new Container(),
     ]);
 
-    await tester.pumpWidget(new TestScrollable(
+    await tester.pumpWidget(new CustomScrollView(
       slivers: <Widget>[
         new SliverList(
           delegate: delegate,

packages/flutter/test/widgets/overscroll_indicator_test.dart

@@ -9,7 +9,6 @@ import 'package:flutter/widgets.dart';
 import 'package:flutter/rendering.dart';
 
 import '../rendering/mock_canvas.dart';
-import 'test_widgets.dart';
 
 final Matcher doesNotOverscroll = isNot(paints..circle());
 
@@ -25,7 +24,7 @@ Future<Null> slowDrag(WidgetTester tester, Point start, Offset offset) async {
 void main() {
   testWidgets('Overscroll indicator color', (WidgetTester tester) async {
     await tester.pumpWidget(
-      new TestScrollable(
+      new CustomScrollView(
         slivers: <Widget>[
           new SliverToBoxAdapter(child: new SizedBox(height: 2000.0)),
         ],
@@ -58,7 +57,7 @@ void main() {
 
   testWidgets('Overscroll indicator changes side when you drag on the other side', (WidgetTester tester) async {
     await tester.pumpWidget(
-      new TestScrollable(
+      new CustomScrollView(
         slivers: <Widget>[
           new SliverToBoxAdapter(child: new SizedBox(height: 2000.0)),
         ],
@@ -93,7 +92,7 @@ void main() {
 
   testWidgets('Overscroll indicator changes side when you shift sides', (WidgetTester tester) async {
     await tester.pumpWidget(
-      new TestScrollable(
+      new CustomScrollView(
         slivers: <Widget>[
           new SliverToBoxAdapter(child: new SizedBox(height: 2000.0)),
         ],
@@ -126,8 +125,7 @@ void main() {
   group('Flipping direction of scrollable doesn\'t change overscroll behavior', () {
     testWidgets('down', (WidgetTester tester) async {
       await tester.pumpWidget(
-        new TestScrollable(
-          axisDirection: AxisDirection.down,
+        new CustomScrollView(
           slivers: <Widget>[
             new SliverToBoxAdapter(child: new SizedBox(height: 20.0)),
           ],
@@ -143,8 +141,8 @@ void main() {
 
     testWidgets('up', (WidgetTester tester) async {
       await tester.pumpWidget(
-        new TestScrollable(
-          axisDirection: AxisDirection.up,
+        new CustomScrollView(
+          reverse: true,
           slivers: <Widget>[
             new SliverToBoxAdapter(child: new SizedBox(height: 20.0)),
           ],
@@ -161,8 +159,7 @@ void main() {
 
   testWidgets('Overscroll in both directions', (WidgetTester tester) async {
     await tester.pumpWidget(
-      new TestScrollable(
-        axisDirection: AxisDirection.down,
+      new CustomScrollView(
         slivers: <Widget>[
           new SliverToBoxAdapter(child: new SizedBox(height: 20.0)),
         ],
@@ -181,8 +178,8 @@ void main() {
 
   testWidgets('Overscroll horizontally', (WidgetTester tester) async {
     await tester.pumpWidget(
-      new TestScrollable(
-        axisDirection: AxisDirection.right,
+      new CustomScrollView(
+        scrollDirection: Axis.horizontal,
         slivers: <Widget>[
           new SliverToBoxAdapter(child: new SizedBox(height: 20.0)),
         ],
@@ -206,8 +203,9 @@ void main() {
     await tester.pumpWidget(
       new ScrollConfiguration2(
         behavior: new TestScrollBehavior1(),
-        child: new TestScrollable(
-          axisDirection: AxisDirection.left,
+        child: new CustomScrollView(
+          scrollDirection: Axis.horizontal,
+          reverse: true,
           slivers: <Widget>[
             new SliverToBoxAdapter(child: new SizedBox(height: 20.0)),
           ],
@@ -223,8 +221,8 @@ void main() {
     await tester.pumpWidget(
       new ScrollConfiguration2(
         behavior: new TestScrollBehavior2(),
-        child: new TestScrollable(
-          axisDirection: AxisDirection.right,
+        child: new CustomScrollView(
+          scrollDirection: Axis.horizontal,
           slivers: <Widget>[
             new SliverToBoxAdapter(child: new SizedBox(height: 20.0)),
           ],

packages/flutter/test/widgets/scroll_controller_test.dart

@@ -108,4 +108,39 @@ void main() {
     expect(controller2.offset, equals(432.0));
     expect(realOffset(), equals(controller2.offset));
   });
+
+  testWidgets('ScrollController control test', (WidgetTester tester) async {
+    ScrollController controller = new ScrollController(
+      initialScrollOffset: 209.0,
+    );
+
+    await tester.pumpWidget(new GridView.count(
+      crossAxisCount: 4,
+      controller: controller,
+      children: kStates.map<Widget>((String state) => new Text(state)).toList(),
+    ));
+
+    double realOffset() {
+      return tester.state<Scrollable2State>(find.byType(Scrollable2)).position.pixels;
+    }
+
+    expect(controller.offset, equals(209.0));
+    expect(realOffset(), equals(controller.offset));
+
+    controller.jumpTo(105.0);
+
+    await tester.pump();
+
+    expect(controller.offset, equals(105.0));
+    expect(realOffset(), equals(controller.offset));
+
+    await tester.pumpWidget(new GridView.count(
+      crossAxisCount: 2,
+      controller: controller,
+      children: kStates.map<Widget>((String state) => new Text(state)).toList(),
+    ));
+
+    expect(controller.offset, equals(105.0));
+    expect(realOffset(), equals(controller.offset));
+  });
 }

packages/flutter/test/widgets/scrollable_custom_scroll_behavior_test.dart

@@ -6,14 +6,18 @@ import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 
-import 'test_widgets.dart';
-
 class TestScrollPosition extends ScrollPosition {
-  TestScrollPosition(
-    TestScrollPhysics physics,
+  TestScrollPosition({
+    ScrollPhysics physics,
     AbstractScrollState state,
     ScrollPosition oldPosition,
-  ) : _pixels = 100.0, super(physics, state, oldPosition);
+  }) : _pixels = 100.0, super(
+    physics: physics,
+    state: state,
+    oldPosition: oldPosition,
+  ) {
+    assert(physics is TestScrollPhysics);
+  }
 
   @override
   TestScrollPhysics get physics => super.physics;
@@ -80,18 +84,23 @@ class TestScrollPosition extends ScrollPosition {
 }
 
 class TestScrollPhysics extends ScrollPhysics {
-  const TestScrollPhysics({ ScrollPhysics parent, this.extentMultiplier }) : super(parent);
+  const TestScrollPhysics({ this.extentMultiplier, ScrollPhysics parent }) : super(parent);
 
   final double extentMultiplier;
 
   @override
-  TestScrollPhysics applyTo(ScrollPhysics parent) {
-    return new TestScrollPhysics(parent: parent, extentMultiplier: extentMultiplier);
+  ScrollPhysics applyTo(ScrollPhysics parent) {
+    return new TestScrollPhysics(
+      extentMultiplier: extentMultiplier,
+      parent: parent,
+    );
   }
+}
 
+class TestScrollController extends ScrollController {
   @override
   ScrollPosition createScrollPosition(ScrollPhysics physics, AbstractScrollState state, ScrollPosition oldPosition) {
-    return new TestScrollPosition(physics, state, oldPosition);
+    return new TestScrollPosition(physics: physics, state: state, oldPosition: oldPosition);
   }
 }
 
@@ -120,7 +129,8 @@ void main() {
   testWidgets('Changing the scroll behavior dynamically', (WidgetTester tester) async {
     await tester.pumpWidget(new ScrollConfiguration2(
       behavior: new TestScrollBehavior(1.0),
-      child: new TestScrollable(
+      child: new CustomScrollView(
+        controller: new TestScrollController(),
         slivers: <Widget>[
           new SliverToBoxAdapter(child: new SizedBox(height: 2000.0)),
         ],
@@ -131,7 +141,8 @@ void main() {
     expect(state.position.getMetrics().extentInside, 1.0);
     await tester.pumpWidget(new ScrollConfiguration2(
       behavior: new TestScrollBehavior(2.0),
-      child: new TestScrollable(
+      child: new CustomScrollView(
+        controller: new TestScrollController(),
         slivers: <Widget>[
           new SliverToBoxAdapter(child: new SizedBox(height: 2000.0)),
         ],

packages/flutter/test/widgets/scrollable_test.dart

@@ -6,14 +6,12 @@ import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 
-import 'test_widgets.dart';
-
 Future<Null> pumpTest(WidgetTester tester, TargetPlatform platform) async {
   await tester.pumpWidget(new MaterialApp(
     theme: new ThemeData(
       platform: platform,
     ),
-    home: new TestScrollable(
+    home: new CustomScrollView(
       slivers: <Widget>[
         new SliverToBoxAdapter(child: new SizedBox(height: 2000.0)),
       ],

packages/flutter/test/widgets/sliver_fill_remaining_test.dart

@@ -5,8 +5,6 @@
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/widgets.dart';
 
-import 'test_widgets.dart';
-
 void main() {
   testWidgets('SliverFillRemaining control test', (WidgetTester tester) async {
     List<Widget> children = new List<Widget>.generate(20, (int i) {
@@ -14,7 +12,7 @@ void main() {
     });
 
     await tester.pumpWidget(
-      new TestScrollable(
+      new CustomScrollView(
         slivers: <Widget>[
           new SliverFill(
             delegate: new SliverChildListDelegate(children),

packages/flutter/test/widgets/slivers_appbar_floating_test.dart

@@ -6,8 +6,6 @@ import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
 
-import 'test_widgets.dart';
-
 void verifyPaintPosition(GlobalKey key, Offset ideal, bool visible) {
   RenderSliver target = key.currentContext.findRenderObject();
   expect(target.parent, new isInstanceOf<RenderViewport2>());
@@ -28,8 +26,7 @@ void main() {
   testWidgets('Sliver appbars - floating - scroll offset doesn\'t change', (WidgetTester tester) async {
     const double bigHeight = 1000.0;
     await tester.pumpWidget(
-      new TestScrollable(
-        axisDirection: AxisDirection.down,
+      new CustomScrollView(
         slivers: <Widget>[
           new BigSliver(height: bigHeight),
           new SliverPersistentHeader(delegate: new TestDelegate(), floating: true),
@@ -56,8 +53,7 @@ void main() {
     const double bigHeight = 1000.0;
     GlobalKey key1, key2, key3;
     await tester.pumpWidget(
-      new TestScrollable(
-        axisDirection: AxisDirection.down,
+      new CustomScrollView(
         slivers: <Widget>[
           new BigSliver(key: key1 = new GlobalKey(), height: bigHeight),
           new SliverPersistentHeader(key: key2 = new GlobalKey(), delegate: delegate, floating: true),
@@ -126,8 +122,7 @@ void main() {
     const double bigHeight = 1000.0;
     GlobalKey key1, key2, key3;
     await tester.pumpWidget(
-      new TestScrollable(
-        axisDirection: AxisDirection.down,
+      new CustomScrollView(
         slivers: <Widget>[
           new BigSliver(key: key1 = new GlobalKey(), height: bigHeight),
           new SliverPersistentHeader(key: key2 = new GlobalKey(), delegate: delegate, floating: true),
@@ -159,8 +154,7 @@ void main() {
     const double bigHeight = 1000.0;
     GlobalKey key1, key2, key3;
     await tester.pumpWidget(
-      new TestScrollable(
-        axisDirection: AxisDirection.down,
+      new CustomScrollView(
         slivers: <Widget>[
           new BigSliver(key: key1 = new GlobalKey(), height: bigHeight),
           new SliverPersistentHeader(key: key2 = new GlobalKey(), delegate: delegate, floating: true),

packages/flutter/test/widgets/slivers_appbar_pinned_test.dart

@@ -6,8 +6,6 @@ import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
 
-import 'test_widgets.dart';
-
 void verifyPaintPosition(GlobalKey key, Offset ideal, bool visible) {
   RenderSliver target = key.currentContext.findRenderObject();
   expect(target.parent, new isInstanceOf<RenderViewport2>());
@@ -29,8 +27,7 @@ void main() {
     const double bigHeight = 550.0;
     GlobalKey key1, key2, key3, key4, key5;
     await tester.pumpWidget(
-      new TestScrollable(
-        axisDirection: AxisDirection.down,
+      new CustomScrollView(
         slivers: <Widget>[
           new BigSliver(key: key1 = new GlobalKey(), height: bigHeight),
           new SliverPersistentHeader(key: key2 = new GlobalKey(), delegate: new TestDelegate(), pinned: true),
@@ -63,8 +60,7 @@ void main() {
     const double bigHeight = 550.0;
     GlobalKey key1, key2, key3, key4, key5;
     await tester.pumpWidget(
-      new TestScrollable(
-        axisDirection: AxisDirection.down,
+      new CustomScrollView(
         slivers: <Widget>[
           new BigSliver(key: key1 = new GlobalKey(), height: bigHeight),
           new SliverPersistentHeader(key: key2 = new GlobalKey(), delegate: new TestDelegate(), pinned: true),
@@ -153,8 +149,7 @@ void main() {
     const double bigHeight = 650.0;
     GlobalKey key1, key2, key3, key4, key5;
     await tester.pumpWidget(
-      new TestScrollable(
-        axisDirection: AxisDirection.down,
+      new CustomScrollView(
         slivers: <Widget>[
           new BigSliver(key: key1 = new GlobalKey(), height: bigHeight),
           new SliverPersistentHeader(key: key2 = new GlobalKey(), delegate: new TestDelegate(), pinned: true),

packages/flutter/test/widgets/slivers_appbar_scrolling_test.dart

@@ -6,8 +6,6 @@ import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
 
-import 'test_widgets.dart';
-
 void verifyPaintPosition(GlobalKey key, Offset ideal) {
   RenderObject target = key.currentContext.findRenderObject();
   expect(target.parent, new isInstanceOf<RenderViewport2>());
@@ -20,8 +18,7 @@ void main() {
   testWidgets('Sliver appbars - scrolling', (WidgetTester tester) async {
     GlobalKey key1, key2, key3, key4, key5;
     await tester.pumpWidget(
-      new TestScrollable(
-        axisDirection: AxisDirection.down,
+      new CustomScrollView(
         slivers: <Widget>[
           new BigSliver(key: key1 = new GlobalKey()),
           new SliverPersistentHeader(key: key2 = new GlobalKey(), delegate: new TestDelegate()),
@@ -54,8 +51,7 @@ void main() {
     GlobalKey key = new GlobalKey();
     TestDelegate delegate = new TestDelegate();
     await tester.pumpWidget(
-      new TestScrollable(
-        axisDirection: AxisDirection.down,
+      new CustomScrollView(
         slivers: <Widget>[
           new BigSliver(),
           new SliverPersistentHeader(key: key, delegate: delegate),

packages/flutter/test/widgets/slivers_evil_test.dart

@@ -7,8 +7,6 @@ import 'package:flutter/rendering.dart';
 import 'package:flutter/physics.dart';
 import 'package:flutter/material.dart';
 
-import 'test_widgets.dart';
-
 class TestSliverPersistentHeaderDelegate extends SliverPersistentHeaderDelegate {
   TestSliverPersistentHeaderDelegate(this._maxExtent);
 
@@ -53,11 +51,11 @@ class TestScrollPhysics extends ClampingScrollPhysics {
 }
 
 class TestViewportScrollPosition extends ScrollPosition {
-  TestViewportScrollPosition(
+  TestViewportScrollPosition({
     ScrollPhysics physics,
     AbstractScrollState state,
     ScrollPosition oldPosition,
-  ) : super(physics, state, oldPosition);
+  }) : super(physics: physics, state: state, oldPosition: oldPosition);
 
   @override
   bool applyContentDimensions(double minScrollExtent, double maxScrollExtent) {
@@ -74,11 +72,15 @@ void main() {
       new ScrollConfiguration2(
         behavior: new TestBehavior(),
         child: new Scrollbar2(
-          child: new TestScrollable(
+          child: new Scrollable2(
             axisDirection: AxisDirection.down,
-            center: centerKey,
-            anchor: 0.25,
             physics: const TestScrollPhysics(),
+            viewportBuilder: (BuildContext context, ViewportOffset offset) {
+              return new Viewport2(
+                axisDirection: AxisDirection.down,
+                anchor: 0.25,
+                offset: offset,
+                center: centerKey,
                 slivers: <Widget>[
                   new SliverToBoxAdapter(child: new Container(height: 5.0)),
                   new SliverToBoxAdapter(child: new Container(height: 520.0)),
@@ -147,6 +149,8 @@ void main() {
                   new SliverToBoxAdapter(child: new Container(height: 520.0)),
                   new SliverToBoxAdapter(child: new Container(height: 5.0)),
                 ],
+              );
+            },
           ),
         ),
       ),

packages/flutter/test/widgets/slivers_protocol_test.dart

@@ -8,8 +8,6 @@ import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
 
-import 'test_widgets.dart';
-
 void verifyPaintPosition(GlobalKey key, Offset ideal) {
   RenderObject target = key.currentContext.findRenderObject();
   expect(target.parent, new isInstanceOf<RenderViewport2>());
@@ -22,8 +20,7 @@ void main() {
   testWidgets('Sliver protocol', (WidgetTester tester) async {
     GlobalKey key1, key2, key3, key4, key5;
     await tester.pumpWidget(
-      new TestScrollable(
-        axisDirection: AxisDirection.down,
+      new CustomScrollView(
         slivers: <Widget>[
           new BigSliver(key: key1 = new GlobalKey()),
           new OverlappingSliver(key: key2 = new GlobalKey()),

packages/flutter/test/widgets/test_widgets.dart

@@ -57,45 +57,3 @@ class FlipWidgetState extends State<FlipWidget> {
 void flipStatefulWidget(WidgetTester tester) {
   tester.state<FlipWidgetState>(find.byType(FlipWidget)).flip();
 }
-
-class TestScrollable extends StatelessWidget {
-  TestScrollable({
-    Key key,
-    this.axisDirection: AxisDirection.down,
-    this.physics,
-    this.anchor: 0.0,
-    this.center,
-    this.slivers: const <Widget>[],
-  }) {
-    assert(slivers != null);
-  }
-
-  final AxisDirection axisDirection;
-
-  final ScrollPhysics physics;
-
-  final double anchor;
-
-  final Key center;
-
-  final List<Widget> slivers;
-
-  Axis get axis => axisDirectionToAxis(axisDirection);
-
-  @override
-  Widget build(BuildContext context) {
-    return new Scrollable2(
-      axisDirection: axisDirection,
-      physics: physics,
-      viewportBuilder: (BuildContext context, ViewportOffset offset) {
-        return new Viewport2(
-          axisDirection: axisDirection,
-          anchor: anchor,
-          offset: offset,
-          center: center,
-          slivers: slivers,
-        );
-      }
-    );
-  }
-}