Add PageView (#7809)

This widget is a start towards replacing PageableList. There are still a number
of features that we'll need to add before this widget can replace PageableList.

dev/manual_tests/pageable_list.dart

@@ -124,9 +124,9 @@ class PageableListAppState extends State<PageableListApp> {
   }
 
   Widget _buildBody(BuildContext context) {
-    return new PageableList(
-      children: cardModels.map(buildCard),
-      itemsWrap: itemsWrap,
+    return new PageView(
+      children: cardModels.map(buildCard).toList(),
+      // TODO(abarth): itemsWrap: itemsWrap,
       scrollDirection: scrollDirection
     );
   }
@@ -150,7 +150,7 @@ void main() {
     theme: new ThemeData(
       brightness: Brightness.light,
       primarySwatch: Colors.blue,
-      accentColor: Colors.redAccent[200]
+      accentColor: Colors.redAccent[200],
     ),
     home: new PageableListApp()
   ));

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

@@ -0,0 +1,49 @@
+// Copyright 2017 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/physics.dart';
+
+import 'scroll_absolute.dart';
+
+class PageScrollPhysics extends ScrollPhysicsProxy {
+  const PageScrollPhysics({
+    ScrollPhysics parent,
+    this.springDescription,
+  }) : super(parent);
+
+  final SpringDescription springDescription;
+
+  @override
+  PageScrollPhysics applyTo(ScrollPhysics parent) {
+    return new PageScrollPhysics(
+      parent: parent,
+      springDescription: springDescription,
+    );
+  }
+
+  double _roundToPage(AbsoluteScrollPosition position, double pixels, double pageSize) {
+    final int index = (pixels + pageSize / 2.0) ~/ pageSize;
+    return (pageSize * index).clamp(position.minScrollExtent, position.maxScrollExtent);
+  }
+
+  double _getTargetPixels(AbsoluteScrollPosition position, double velocity) {
+    final double pageSize = position.viewportDimension;
+    if (velocity < -position.scrollTolerances.velocity)
+      return _roundToPage(position, position.pixels - pageSize / 2.0, pageSize);
+    if (velocity > position.scrollTolerances.velocity)
+      return _roundToPage(position, position.pixels + pageSize / 2.0, pageSize);
+    return _roundToPage(position, position.pixels, pageSize);
+  }
+
+  @override
+  Simulation createBallisticSimulation(AbsoluteScrollPosition position, double velocity) {
+    // If we're out of range and not headed back in range, defer to the parent
+    // ballistics, which should put us back in range at a page boundary.
+    if ((velocity <= 0.0 && position.pixels <= position.minScrollExtent) ||
+        (velocity >= 0.0 && position.pixels >= position.maxScrollExtent))
+      return super.createBallisticSimulation(position, velocity);
+    final double target = _getTargetPixels(position, velocity);
+    return new ScrollSpringSimulation(scrollSpring, position.pixels, target, velocity);
+  }
+}

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

@@ -94,9 +94,16 @@ class ViewportScrollBehavior extends ScrollBehavior2 {
     return null;
   }
 
+  ScrollPhysics _getEffectiveScrollPhysics(BuildContext context, ScrollPhysics physics) {
+    final ScrollPhysics defaultPhysics = getScrollPhysics(getPlatform(context));
+    if (physics != null)
+      return physics.applyTo(defaultPhysics);
+    return defaultPhysics;
+  }
+
   @override
-  ScrollPosition createScrollPosition(BuildContext context, Scrollable2State state, ScrollPosition oldPosition) {
-    return new AbsoluteScrollPosition(state, scrollTolerances, oldPosition, getScrollPhysics(getPlatform(context)));
+  ScrollPosition createScrollPosition(BuildContext context, Scrollable2State state, ScrollPosition oldPosition, ScrollPhysics physics) {
+    return new AbsoluteScrollPosition(state, scrollTolerances, oldPosition, _getEffectiveScrollPhysics(context, physics));
   }
 
   @override
@@ -108,6 +115,8 @@ class ViewportScrollBehavior extends ScrollBehavior2 {
 abstract class ScrollPhysics {
   const ScrollPhysics();
 
+  ScrollPhysicsProxy applyTo(ScrollPhysics parent) => this;
+
   /// Used by [AbsoluteDragScrollActivity] and other user-driven activities to
   /// convert an offset in logical pixels as provided by the [DragUpdateDetails]
   /// into a delta to apply using [setPixels].
@@ -133,6 +142,58 @@ abstract class ScrollPhysics {
   /// [AbsoluteBallisticScrollActivity] with the returned value. Otherwise, the
   /// [ScrollPosition] will begin an idle activity instead.
   Simulation createBallisticSimulation(AbsoluteScrollPosition position, double velocity) => null;
+
+  static final SpringDescription _kDefaultScrollSpring = new SpringDescription.withDampingRatio(
+    mass: 0.5,
+    springConstant: 100.0,
+    ratio: 1.1,
+  );
+
+  SpringDescription get scrollSpring => _kDefaultScrollSpring;
+}
+
+abstract class ScrollPhysicsProxy extends ScrollPhysics {
+  const ScrollPhysicsProxy(this.parent);
+
+  final ScrollPhysics parent;
+
+  @override
+  ScrollPhysicsProxy applyTo(ScrollPhysics parent) {
+    throw new FlutterError(
+      '$runtimeType must override applyTo.\n'
+      'The default implementation of applyTo is not appropriate for subclasses '
+      'of ScrollPhysicsProxy because they should return an instance of themselves '
+      'with their parent property replaced with the given ScrollPhysics instance.'
+    );
+  }
+
+  @override
+  double applyPhysicsToUserOffset(AbsoluteScrollPosition position, double offset) {
+    if (parent == null)
+      return super.applyPhysicsToUserOffset(position, offset);
+    return parent.applyPhysicsToUserOffset(position, offset);
+  }
+
+  @override
+  double applyBoundaryConditions(AbsoluteScrollPosition position, double value) {
+    if (parent == null)
+      return super.applyBoundaryConditions(position, value);
+    return parent.applyBoundaryConditions(position, value);
+  }
+
+  @override
+  Simulation createBallisticSimulation(AbsoluteScrollPosition position, double velocity) {
+    if (parent == null)
+      return super.createBallisticSimulation(position, velocity);
+    return parent.createBallisticSimulation(position, velocity);
+  }
+
+  @override
+  SpringDescription get scrollSpring {
+    if (parent == null)
+      return super.scrollSpring;
+    return parent.scrollSpring;
+  }
 }
 
 class AbsoluteScrollPosition extends ScrollPosition {
@@ -405,6 +466,7 @@ class BouncingScrollPhysics extends ScrollPhysics {
   Simulation createBallisticSimulation(AbsoluteScrollPosition position, double velocity) {
     if (velocity.abs() >= position.scrollTolerances.velocity || position.outOfRange) {
       return new BouncingScrollSimulation(
+        spring: scrollSpring,
         position: position.pixels,
         velocity: velocity,
         leadingExtent: position.minScrollExtent,
@@ -446,19 +508,13 @@ class ClampingScrollPhysics extends ScrollPhysics {
     return 0.0;
   }
 
-  static final SpringDescription _defaultScrollSpring = new SpringDescription.withDampingRatio(
-    mass: 0.5,
-    springConstant: 100.0,
-    ratio: 1.1,
-  );
-
   @override
   Simulation createBallisticSimulation(AbsoluteScrollPosition position, double velocity) {
     if (position.outOfRange) {
       if (position.pixels > position.maxScrollExtent)
-        return new ScrollSpringSimulation(_defaultScrollSpring, position.pixels, position.maxScrollExtent, math.min(0.0, velocity));
+        return new ScrollSpringSimulation(scrollSpring, position.pixels, position.maxScrollExtent, math.min(0.0, velocity));
       if (position.pixels < position.minScrollExtent)
-        return new ScrollSpringSimulation(_defaultScrollSpring, position.pixels, position.minScrollExtent, math.max(0.0, velocity));
+        return new ScrollSpringSimulation(scrollSpring, position.pixels, position.minScrollExtent, math.max(0.0, velocity));
       assert(false);
     }
     if (!position.atEdge && velocity.abs() >= position.scrollTolerances.velocity) {

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

@@ -33,10 +33,10 @@ class BouncingScrollSimulation extends SimulationGroup {
     @required double velocity,
     @required double leadingExtent,
     @required double trailingExtent,
-    SpringDescription spring,
+    @required SpringDescription spring,
   }) : _leadingExtent = leadingExtent,
        _trailingExtent = trailingExtent,
-       _spring = spring ?? _defaultScrollSpring {
+       _spring = spring {
     assert(position != null);
     assert(velocity != null);
     assert(_leadingExtent != null);
@@ -50,12 +50,6 @@ class BouncingScrollSimulation extends SimulationGroup {
   final double _trailingExtent;
   final SpringDescription _spring;
 
-  static final SpringDescription _defaultScrollSpring = new SpringDescription.withDampingRatio(
-    mass: 0.5,
-    springConstant: 100.0,
-    ratio: 1.1,
-  );
-
   bool _isSpringing = false;
   Simulation _currentSimulation;
   double _offset = 0.0;

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

@@ -7,6 +7,8 @@ import 'package:meta/meta.dart';
 
 import 'framework.dart';
 import 'basic.dart';
+import 'page_scroll_physics.dart';
+import 'scroll_absolute.dart';
 import 'scrollable.dart';
 import 'sliver.dart';
 import 'viewport.dart';
@@ -20,6 +22,7 @@ class ScrollView extends StatelessWidget {
     this.padding,
     this.initialScrollOffset: 0.0,
     this.itemExtent,
+    this.physics,
     this.shrinkWrap: false,
     this.children: const <Widget>[],
   }) : super(key: key) {
@@ -38,6 +41,8 @@ class ScrollView extends StatelessWidget {
 
   final double itemExtent;
 
+  final ScrollPhysics physics;
+
   final bool shrinkWrap;
 
   final List<Widget> children;
@@ -76,6 +81,7 @@ class ScrollView extends StatelessWidget {
     return new Scrollable2(
       axisDirection: axisDirection,
       initialScrollOffset: initialScrollOffset,
+      physics: physics,
       viewportBuilder: (BuildContext context, ViewportOffset offset) {
         if (shrinkWrap) {
           return new ShrinkWrappingViewport(
@@ -166,3 +172,21 @@ class ScrollGrid extends ScrollView {
     );
   }
 }
+
+class PageView extends ScrollView {
+  PageView({
+    Key key,
+    Axis scrollDirection: Axis.horizontal,
+    List<Widget> children: const <Widget>[],
+  }) : super(
+    key: key,
+    scrollDirection: scrollDirection,
+    physics: const PageScrollPhysics(),
+    children: children,
+  );
+
+  @override
+  Widget buildChildLayout(BuildContext context) {
+    return new SliverFill(delegate: childrenDelegate);
+  }
+}

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

@@ -20,13 +20,15 @@ import 'framework.dart';
 import 'gesture_detector.dart';
 import 'notification_listener.dart';
 import 'page_storage.dart';
-import 'scroll_absolute.dart' show ViewportScrollBehavior;
 import 'scroll_behavior.dart';
 import 'scroll_configuration.dart';
 import 'scroll_notification.dart';
 import 'ticker_provider.dart';
 import 'viewport.dart';
 
+// TODO(abarth): Merge AbsoluteScrollPosition and ScrollPosition.
+import 'scroll_absolute.dart' show ViewportScrollBehavior, ScrollPhysics;
+
 export 'package:flutter/physics.dart' show Tolerance;
 
 // This file defines an unopinionated scrolling mechanism.
@@ -360,7 +362,7 @@ abstract class ScrollBehavior2 {
   /// object must be disposed (via [ScrollPosition.oldPosition]) in the same
   /// call stack. Passing a non-null `oldPosition` is a destructive operation
   /// for that [ScrollPosition].
-  ScrollPosition createScrollPosition(BuildContext context, Scrollable2State state, ScrollPosition oldPosition);
+  ScrollPosition createScrollPosition(BuildContext context, Scrollable2State state, ScrollPosition oldPosition, ScrollPhysics physics);
 
   /// Whether this delegate is different than the old delegate, or would now
   /// return meaningfully different widgets from [wrap] or a meaningfully
@@ -405,6 +407,7 @@ class Scrollable2 extends StatefulWidget {
     Key key,
     this.initialScrollOffset: 0.0,
     this.axisDirection: AxisDirection.down,
+    this.physics,
     this.scrollBehavior,
     @required this.viewportBuilder,
   }) : super (key: key) {
@@ -417,6 +420,8 @@ class Scrollable2 extends StatefulWidget {
 
   final AxisDirection axisDirection;
 
+  final ScrollPhysics physics;
+
   /// The delegate that creates the [ScrollPosition] and wraps the viewport
   /// in extra widgets (e.g. for overscroll effects).
   ///
@@ -484,7 +489,7 @@ class Scrollable2State extends State<Scrollable2> with TickerProviderStateMixin
   void _updatePosition() {
     _scrollBehavior = config.scrollBehavior ?? Scrollable2.getScrollBehavior(context);
     final ScrollPosition oldPosition = position;
-    _position = _scrollBehavior.createScrollPosition(context, this, oldPosition);
+    _position = _scrollBehavior.createScrollPosition(context, this, oldPosition, config.physics);
     assert(position != null);
     if (oldPosition != null) {
       // It's important that we not do this until after the viewport has had a

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

@@ -54,8 +54,6 @@ abstract class SliverChildDelegate {
 // /// demand). For example, the body of a dialog box might fit both of these
 // /// conditions.
 class SliverChildListDelegate extends SliverChildDelegate {
-  /// Abstract const constructor. This constructor enables subclasses to provide
-  /// const constructors so that they can be used in const expressions.
   const SliverChildListDelegate(this.children);
 
   final List<Widget> children;

packages/flutter/test/material/stepper_test.dart

@@ -313,9 +313,7 @@ void main() {
 
     await tester.pump(const Duration(milliseconds: 100));
     expect(scrollableState.position.pixels, greaterThan(0.0));
-  }, skip: Scrollable == Scrollable &&
-           ScrollableViewport == ScrollableViewport &&
-           Block == Block); // TODO(abarth): re-enable when ensureVisible is implemented
+  }, skip: Scrollable != Scrollable2); // TODO(abarth): re-enable when ensureVisible is implemented
 
   testWidgets('Stepper index test', (WidgetTester tester) async {
     await tester.pumpWidget(

packages/flutter/test/widgets/page_view_test.dart

@@ -0,0 +1,76 @@
+// Copyright 2017 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_test/flutter_test.dart';
+import 'package:flutter/widgets.dart';
+
+import 'states.dart';
+
+const Duration _frameDuration = const Duration(milliseconds: 100);
+
+void main() {
+  testWidgets('PageView control test', (WidgetTester tester) async {
+    List<String> log = <String>[];
+
+    await tester.pumpWidget(new PageView(
+      children: kStates.map<Widget>((String state) {
+        return new GestureDetector(
+          onTap: () {
+            log.add(state);
+          },
+          child: new Container(
+            height: 200.0,
+            decoration: const BoxDecoration(
+              backgroundColor: const Color(0xFF0000FF),
+            ),
+            child: new Text(state),
+          ),
+        );
+      }).toList()
+    ));
+
+    await tester.tap(find.text('Alabama'));
+    expect(log, equals(<String>['Alabama']));
+    log.clear();
+
+    expect(find.text('Alaska'), findsNothing);
+
+    await tester.scroll(find.byType(PageView), const Offset(-10.0, 0.0));
+    await tester.pump();
+
+    expect(find.text('Alabama'), findsOneWidget);
+    expect(find.text('Alaska'), findsOneWidget);
+    expect(find.text('Arizona'), findsNothing);
+
+    await tester.pumpUntilNoTransientCallbacks(_frameDuration);
+
+    expect(find.text('Alabama'), findsOneWidget);
+    expect(find.text('Alaska'), findsNothing);
+
+    await tester.scroll(find.byType(PageView), const Offset(-401.0, 0.0));
+    await tester.pumpUntilNoTransientCallbacks(_frameDuration);
+
+    expect(find.text('Alabama'), findsNothing);
+    expect(find.text('Alaska'), findsOneWidget);
+    expect(find.text('Arizona'), findsNothing);
+
+    await tester.tap(find.text('Alaska'));
+    expect(log, equals(<String>['Alaska']));
+    log.clear();
+
+    await tester.fling(find.byType(PageView), const Offset(-200.0, 0.0), 1000.0);
+    await tester.pumpUntilNoTransientCallbacks(_frameDuration);
+
+    expect(find.text('Alabama'), findsNothing);
+    expect(find.text('Alaska'), findsNothing);
+    expect(find.text('Arizona'), findsOneWidget);
+
+    await tester.fling(find.byType(PageView), const Offset(200.0, 0.0), 1000.0);
+    await tester.pumpUntilNoTransientCallbacks(_frameDuration);
+
+    expect(find.text('Alabama'), findsNothing);
+    expect(find.text('Alaska'), findsOneWidget);
+    expect(find.text('Arizona'), findsNothing);
+  });
+}

packages/flutter/test/widgets/scrollable_custom_scroll_behavior_test.dart

@@ -78,7 +78,7 @@ class TestScrollBehavior extends ScrollBehavior2 {
   Widget wrap(BuildContext context, Widget child, AxisDirection axisDirection) => child;
 
   @override
-  ScrollPosition createScrollPosition(BuildContext context, Scrollable2State state, ScrollPosition oldPosition) {
+  ScrollPosition createScrollPosition(BuildContext context, Scrollable2State state, ScrollPosition oldPosition, ScrollPhysics physics) {
     return new TestScrollPosition(extentMultiplier, state, ViewportScrollBehavior.defaultScrollTolerances, oldPosition);
   }
 

packages/flutter/test/widgets/slivers_evil_test.dart

@@ -42,12 +42,12 @@ class TestBehavior extends ScrollBehavior2 {
   }
 
   @override
-  ScrollPosition createScrollPosition(BuildContext context, Scrollable2State state, ScrollPosition oldPosition) {
+  ScrollPosition createScrollPosition(BuildContext context, Scrollable2State state, ScrollPosition oldPosition, ScrollPhysics physics) {
     return new TestViewportScrollPosition(
       state,
       new Tolerance(velocity: 20.0, distance: 1.0),
       oldPosition,
-      const ClampingScrollPhysics(),
+      physics,
     );
   }
 
@@ -80,6 +80,7 @@ void main() {
           axisDirection: AxisDirection.down,
           center: centerKey,
           anchor: 0.25,
+          physics: const ClampingScrollPhysics(),
           scrollBehavior: new TestBehavior(),
           slivers: <Widget>[
             new SliverToBoxAdapter(child: new Container(height: 5.0)),

packages/flutter/test/widgets/test_widgets.dart

@@ -63,6 +63,7 @@ class TestScrollable extends StatelessWidget {
     Key key,
     this.initialScrollOffset: 0.0,
     this.axisDirection: AxisDirection.down,
+    this.physics,
     this.anchor: 0.0,
     this.center,
     this.scrollBehavior,
@@ -75,6 +76,8 @@ class TestScrollable extends StatelessWidget {
 
   final AxisDirection axisDirection;
 
+  final ScrollPhysics physics;
+
   final double anchor;
 
   final Key center;
@@ -90,6 +93,7 @@ class TestScrollable extends StatelessWidget {
     return new Scrollable2(
       initialScrollOffset: initialScrollOffset,
       axisDirection: axisDirection,
+      physics: physics,
       scrollBehavior: scrollBehavior,
       viewportBuilder: (BuildContext context, ViewportOffset offset) {
         return new Viewport2(
@@ -102,4 +106,4 @@ class TestScrollable extends StatelessWidget {
       }
     );
   }
-}
+}