Port remaining ScrollableViewport tests to SingleChildScrollView (#8129)

Also, rename ScrollableMetrics to ScrollMetrics, which follows the
naming convention for most of the other classes (e.g., ScrollPosition,
ScrollPhysics).

Finally, fix a bug whereby SingleChildScrollView could not have a
GlobalKey, because, write test, find bug.

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

@@ -98,7 +98,7 @@ class _ScrollbarController extends ChangeNotifier {
     super.dispose();
   }
 
-  ScrollableMetrics _lastMetrics;
+  ScrollMetrics _lastMetrics;
   AxisDirection _lastAxisDirection;
 
   static const double _kMinThumbExtent = 18.0;
@@ -106,7 +106,7 @@ class _ScrollbarController extends ChangeNotifier {
   static const Duration _kThumbFadeDuration = const Duration(milliseconds: 300);
   static const Duration _kFadeOutTimeout = const Duration(milliseconds: 600);
 
-  void update(ScrollableMetrics metrics, AxisDirection axisDirection) {
+  void update(ScrollMetrics metrics, AxisDirection axisDirection) {
     _lastMetrics = metrics;
     _lastAxisDirection = axisDirection;
     if (_fadeController.status == AnimationStatus.completed) {

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

@@ -2,6 +2,10 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+////////////////////////////////////////////////////////////////////////////////
+// DELETE THIS FILE WHEN REMOVING LEGACY SCROLLING CODE
+////////////////////////////////////////////////////////////////////////////////
+
 import 'package:flutter/foundation.dart';
 
 import 'framework.dart';

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

@@ -189,7 +189,7 @@ class PageView extends BoxScrollView {
     return new NotificationListener<ScrollNotification2>(
       onNotification: (ScrollNotification2 notification) {
         if (notification.depth == 1 && onPageChanged != null && notification is ScrollEndNotification) {
-          final ScrollableMetrics metrics = notification.metrics;
+          final ScrollMetrics metrics = notification.metrics;
           onPageChanged(metrics.extentBefore ~/ metrics.viewportDimension);
         }
         return false;

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

@@ -18,11 +18,11 @@ import 'scrollable.dart' show Scrollable2, Scrollable2State;
 /// not defined, but must be consistent. For example, they could be in pixels,
 /// or in percentages, or in units of the [extentInside] (in the latter case,
 /// [extentInside] would always be 1.0).
-class ScrollableMetrics {
+class ScrollMetrics {
   /// Create a description of the metrics of a [Scrollable2]'s contents.
   ///
   /// The three arguments must be present, non-null, finite, and non-negative.
-  const ScrollableMetrics({
+  const ScrollMetrics({
     @required this.extentBefore,
     @required this.extentInside,
     @required this.extentAfter,
@@ -34,9 +34,11 @@ class ScrollableMetrics {
   /// described by [extentInside].
   final double extentBefore;
 
-  /// The quantity of visible content. If [extentBefore] and [extentAfter] are
-  /// non-zero, then this is typically the height of the viewport. It could be
-  /// less if there is less content visible than the size of the viewport.
+  /// The quantity of visible content.
+  ///
+  /// If [extentBefore] and [extentAfter] are non-zero, then this is typically
+  /// the height of the viewport. It could be less if there is less content
+  /// visible than the size of the viewport.
   final double extentInside;
 
   /// The quantity of content conceptually "below" the currently visible content
@@ -65,13 +67,12 @@ abstract class ScrollNotification2 extends LayoutChangedNotification {
 
   Axis get axis => axisDirectionToAxis(axisDirection);
 
-  final ScrollableMetrics metrics;
+  final ScrollMetrics metrics;
 
   /// The build context of the [Scrollable2] that fired this notification.
   ///
   /// This can be used to find the scrollable's render objects to determine the
   /// size of the viewport, for instance.
-  // TODO(ianh): Maybe just fold those into the ScrollableMetrics?
   final BuildContext context;
 
   /// The number of [Scrollable2] widgets that this notification has bubbled

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

@@ -228,8 +228,8 @@ class ScrollPosition extends ViewportOffset {
   /// The metrics do not need to be in absolute (pixel) units, but they must be
   /// in consistent units (so that they can be compared over time or used to
   /// drive diagrammatic user interfaces such as scrollbars).
-  ScrollableMetrics getMetrics() {
-    return new ScrollableMetrics(
+  ScrollMetrics getMetrics() {
+    return new ScrollMetrics(
       extentBefore: math.max(pixels - minScrollExtent, 0.0),
       extentInside: math.min(pixels, maxScrollExtent) - math.max(pixels, minScrollExtent) + math.min(viewportDimension, maxScrollExtent - minScrollExtent),
       extentAfter: math.max(maxScrollExtent - pixels, 0.0),

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

@@ -84,7 +84,6 @@ class SingleChildScrollView extends StatelessWidget {
       physics: physics,
       viewportBuilder: (BuildContext context, ViewportOffset offset) {
         return new _SingleChildViewport(
-          key: key,
           axisDirection: axisDirection,
           offset: offset,
           child: contents,

packages/flutter/test/widgets/clamp_overscrolls_test.dart

@@ -11,28 +11,26 @@ import 'package:flutter/widgets.dart';
 // The top of the bottom widget is at 550 (the top of the top widget
 // is at 0). The top of the bottom widget is 500 when it has been
 // scrolled completely into view.
-Widget buildFrame(ScrollableEdge clampedEdge) {
-  return new ClampOverscrolls(
-    edge: clampedEdge,
-    child: new ScrollableViewport(
-      key: new UniqueKey(),
-      child: new SizedBox(
-        height: 650.0,
-        child: new Column(
-          crossAxisAlignment: CrossAxisAlignment.start,
-          children: <Widget>[
-            new SizedBox(height: 100.0, child: new Text('top')),
-            new Expanded(child: new Container()),
-            new SizedBox(height: 100.0, child: new Text('bottom')),
-          ]
-        )
-      )
-    )
+Widget buildFrame(ScrollPhysics physics) {
+  return new SingleChildScrollView(
+    key: new UniqueKey(),
+    physics: physics,
+    child: new SizedBox(
+      height: 650.0,
+      child: new Column(
+        crossAxisAlignment: CrossAxisAlignment.start,
+        children: <Widget>[
+          new SizedBox(height: 100.0, child: new Text('top')),
+          new Expanded(child: new Container()),
+          new SizedBox(height: 100.0, child: new Text('bottom')),
+        ],
+      ),
+    ),
   );
 }
 
 void main() {
-  testWidgets('ClampOverscrolls', (WidgetTester tester) async {
+  testWidgets('ClampingScrollPhysics', (WidgetTester tester) async {
 
     // Scroll the target text widget by offset and then return its origin
     // in global coordinates.
@@ -45,105 +43,49 @@ void main() {
       return new Future<Point>.value(widgetOrigin);
     }
 
-    // Each of the blocks below test overscrolling the top and bottom
-    // with a value for ClampOverscrolls.edge.
-
-    await tester.pumpWidget(buildFrame(ScrollableEdge.none));
+    await tester.pumpWidget(buildFrame(const BouncingScrollPhysics()));
     Point origin = await locationAfterScroll('top', const Offset(0.0, 400.0));
     expect(origin.y, greaterThan(0.0));
     origin = await locationAfterScroll('bottom', const Offset(0.0, -400.0));
     expect(origin.y, lessThan(500.0));
 
 
-    await tester.pumpWidget(buildFrame(ScrollableEdge.both));
+    await tester.pumpWidget(buildFrame(const ClampingScrollPhysics()));
     origin = await locationAfterScroll('top', const Offset(0.0, 400.0));
     expect(origin.y, equals(0.0));
     origin = await locationAfterScroll('bottom', const Offset(0.0, -400.0));
     expect(origin.y, equals(500.0));
-
-    await tester.pumpWidget(buildFrame(ScrollableEdge.leading));
-    origin = await locationAfterScroll('top', const Offset(0.0, 400.0));
-    expect(origin.y, equals(0.0));
-    origin = await locationAfterScroll('bottom', const Offset(0.0, -400.0));
-    expect(origin.y, lessThan(500.0));
-
-    await tester.pumpWidget(buildFrame(ScrollableEdge.trailing));
-    origin = await locationAfterScroll('top', const Offset(0.0, 400.0));
-    expect(origin.y, greaterThan(0.0));
-    origin = await locationAfterScroll('bottom', const Offset(0.0, -400.0));
-    expect(origin.y, equals(500.0));
   });
 
-  testWidgets('ClampOverscrolls affects scrollOffset not virtualScrollOffset', (WidgetTester tester) async {
+  testWidgets('ClampingScrollPhysics affects ScrollPosition', (WidgetTester tester) async {
 
-    // ClampOverscrolls.edge == ScrollableEdge.none
+    // BouncingScrollPhysics
 
-    await tester.pumpWidget(buildFrame(ScrollableEdge.none));
-    StatefulElement statefulElement = tester.element(find.byType(Scrollable));
-    ScrollableState scrollable = statefulElement.state;
+    await tester.pumpWidget(buildFrame(const BouncingScrollPhysics()));
+    Scrollable2State scrollable = tester.state(find.byType(Scrollable2));
 
     await tester.scrollAt(tester.getTopLeft(find.text('top')), const Offset(0.0, 400.0));
     await tester.pump();
-    expect(scrollable.scrollOffset, lessThan(0.0));
-    expect(scrollable.virtualScrollOffset, equals(scrollable.scrollOffset));
+    expect(scrollable.position.pixels, lessThan(0.0));
     await tester.pump(const Duration(seconds: 1)); // Allow overscroll to settle
 
     await tester.scrollAt(tester.getTopLeft(find.text('bottom')), const Offset(0.0, -400.0));
     await tester.pump();
-    expect(scrollable.scrollOffset, greaterThan(0.0));
-    expect(scrollable.virtualScrollOffset, equals(scrollable.scrollOffset));
+    expect(scrollable.position.pixels, greaterThan(0.0));
     await tester.pump(const Duration(seconds: 1)); // Allow overscroll to settle
 
-    // ClampOverscrolls.edge == ScrollableEdge.both
-
-    await tester.pumpWidget(buildFrame(ScrollableEdge.both));
-    statefulElement = tester.element(find.byType(Scrollable));
-    scrollable = statefulElement.state;
-
-    await tester.scrollAt(tester.getTopLeft(find.text('top')), const Offset(0.0, 400.0));
-    await tester.pump();
-    expect(scrollable.scrollOffset, equals(0.0));
-    expect(scrollable.virtualScrollOffset, lessThan(0.0));
-    await tester.pump(const Duration(seconds: 1)); // Allow overscroll to settle
-
-    await tester.scrollAt(tester.getTopLeft(find.text('bottom')), const Offset(0.0, -400.0));
-    await tester.pump();
-    expect(scrollable.scrollOffset, equals(50.0));
-    expect(scrollable.virtualScrollOffset, greaterThan(50.0));
-
-    // ClampOverscrolls.edge == ScrollableEdge.leading
-
-    await tester.pumpWidget(buildFrame(ScrollableEdge.leading));
-    statefulElement = tester.element(find.byType(Scrollable));
-    scrollable = statefulElement.state;
-
-    await tester.scrollAt(tester.getTopLeft(find.text('top')), const Offset(0.0, 400.0));
-    await tester.pump();
-    expect(scrollable.scrollOffset, equals(0.0));
-    expect(scrollable.virtualScrollOffset, lessThan(0.0));
-    await tester.pump(const Duration(seconds: 1)); // Allow overscroll to settle
-
-    await tester.scrollAt(tester.getTopLeft(find.text('bottom')), const Offset(0.0, -400.0));
-    await tester.pump();
-    expect(scrollable.scrollOffset, greaterThan(0.0));
-    expect(scrollable.virtualScrollOffset, equals(scrollable.scrollOffset));
-
-    // ClampOverscrolls.edge == ScrollableEdge.trailing
+    // ClampingScrollPhysics
 
-    await tester.pumpWidget(buildFrame(ScrollableEdge.trailing));
-    statefulElement = tester.element(find.byType(Scrollable));
-    scrollable = statefulElement.state;
+    await tester.pumpWidget(buildFrame(const ClampingScrollPhysics()));
+    scrollable = scrollable = tester.state(find.byType(Scrollable2));
 
     await tester.scrollAt(tester.getTopLeft(find.text('top')), const Offset(0.0, 400.0));
     await tester.pump();
-    expect(scrollable.scrollOffset, lessThan(0.0));
-    expect(scrollable.virtualScrollOffset, equals(scrollable.scrollOffset));
-    expect(scrollable.virtualScrollOffset, equals(scrollable.scrollOffset));
+    expect(scrollable.position.pixels, equals(0.0));
     await tester.pump(const Duration(seconds: 1)); // Allow overscroll to settle
 
     await tester.scrollAt(tester.getTopLeft(find.text('bottom')), const Offset(0.0, -400.0));
     await tester.pump();
-    expect(scrollable.scrollOffset, equals(50.0));
-    expect(scrollable.virtualScrollOffset, greaterThan(50.0));
+    expect(scrollable.position.pixels, equals(50.0));
   });
 }

packages/flutter/test/widgets/scroll_behavior_test.dart

@@ -2,110 +2,70 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'package:flutter/foundation.dart' show defaultTargetPlatform;
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
 
-class TestScrollConfigurationDelegate extends ScrollConfigurationDelegate {
-  TestScrollConfigurationDelegate(this.flag);
+class TestScrollBehavior extends ScrollBehavior2 {
+  TestScrollBehavior(this.flag);
 
   final bool flag;
 
   @override
-  TargetPlatform get platform => defaultTargetPlatform;
-
-  @override
-  ExtentScrollBehavior createScrollBehavior() {
+  ScrollPhysics getScrollPhysics(BuildContext context) {
     return flag
-      ? new BoundedBehavior(platform: platform)
-      : new UnboundedBehavior(platform: platform);
+      ? const ClampingScrollPhysics()
+      : const BouncingScrollPhysics();
   }
 
   @override
-  bool updateShouldNotify(TestScrollConfigurationDelegate old) => flag != old.flag;
+  bool shouldNotify(TestScrollBehavior old) => flag != old.flag;
 }
 
 void main() {
-  test('BoundedBehavior min scroll offset', () {
-    BoundedBehavior behavior = new BoundedBehavior(
-      contentExtent: 150.0,
-      containerExtent: 75.0,
-      minScrollOffset: -100.0,
-      platform: TargetPlatform.iOS
-    );
-
-    expect(behavior.minScrollOffset, equals(-100.0));
-    expect(behavior.maxScrollOffset, equals(-25.0));
-
-    double scrollOffset = behavior.updateExtents(
-      contentExtent: 125.0,
-      containerExtent: 50.0,
-      scrollOffset: -80.0
-    );
-
-    expect(behavior.minScrollOffset, equals(-100.0));
-    expect(behavior.maxScrollOffset, equals(-25.0));
-    expect(scrollOffset, equals(-80.0));
-
-    scrollOffset = behavior.updateExtents(
-      minScrollOffset: 50.0,
-      scrollOffset: scrollOffset
-    );
-
-    expect(behavior.minScrollOffset, equals(50.0));
-    expect(behavior.maxScrollOffset, equals(125.0));
-    expect(scrollOffset, equals(50.0));
-  });
-
   testWidgets('Inherited ScrollConfiguration changed', (WidgetTester tester) async {
     final GlobalKey key = new GlobalKey(debugLabel: 'scrollable');
-    TestScrollConfigurationDelegate delegate;
-    ExtentScrollBehavior behavior;
+    TestScrollBehavior behavior;
+    ScrollPosition position;
+
+    Widget scrollView = new SingleChildScrollView(
+      key: key,
+      child: new Builder(
+        builder: (BuildContext context) {
+          behavior = ScrollConfiguration2.of(context);
+          position = Scrollable2.of(context).position;
+          return new Container(height: 1000.0);
+        },
+      ),
+    );
 
     await tester.pumpWidget(
-      new ScrollConfiguration(
-        delegate: new TestScrollConfigurationDelegate(true),
-        child: new ScrollableViewport(
-          key: key,
-          child: new Builder(
-            builder: (BuildContext context) {
-              delegate = ScrollConfiguration.of(context);
-              behavior = Scrollable.of(context).scrollBehavior;
-              return new Container(height: 1000.0);
-            }
-          )
-        )
-      )
+      new ScrollConfiguration2(
+        behavior: new TestScrollBehavior(true),
+        child: scrollView,
+      ),
     );
 
-    expect(delegate, isNotNull);
-    expect(delegate.flag, isTrue);
-    expect(behavior, const isInstanceOf<BoundedBehavior>());
-    expect(behavior.contentExtent, equals(1000.0));
-    expect(behavior.containerExtent, equals(600.0));
+    expect(behavior, isNotNull);
+    expect(behavior.flag, isTrue);
+    expect(position.physics, const isInstanceOf<ClampingScrollPhysics>());
+    ScrollMetrics metrics = position.getMetrics();
+    expect(metrics.extentAfter, equals(400.0));
+    expect(metrics.viewportDimension, equals(600.0));
 
     // Same Scrollable, different ScrollConfiguration
     await tester.pumpWidget(
-      new ScrollConfiguration(
-        delegate: new TestScrollConfigurationDelegate(false),
-        child: new ScrollableViewport(
-          key: key,
-          child: new Builder(
-            builder: (BuildContext context) {
-              delegate = ScrollConfiguration.of(context);
-              behavior = Scrollable.of(context).scrollBehavior;
-              return new Container(height: 1000.0);
-            }
-          )
-        )
-      )
+      new ScrollConfiguration2(
+        behavior: new TestScrollBehavior(false),
+        child: scrollView,
+      ),
     );
 
-    expect(delegate, isNotNull);
-    expect(delegate.flag, isFalse);
-    expect(behavior, const isInstanceOf<UnboundedBehavior>());
+    expect(behavior, isNotNull);
+    expect(behavior.flag, isFalse);
+    expect(position.physics, const isInstanceOf<BouncingScrollPhysics>());
     // Regression test for https://github.com/flutter/flutter/issues/5856
-    expect(behavior.contentExtent, equals(1000.0));
-    expect(behavior.containerExtent, equals(600.0));
+    metrics = position.getMetrics();
+    expect(metrics.extentAfter, equals(400.0));
+    expect(metrics.viewportDimension, equals(600.0));
   });
 }

packages/flutter/test/widgets/scrollable_custom_scroll_behavior_test.dart

@@ -41,19 +41,19 @@ class TestScrollPosition extends ScrollPosition {
   }
 
   @override
-  ScrollableMetrics getMetrics() {
+  ScrollMetrics getMetrics() {
     double insideExtent = viewportDimension;
     double beforeExtent = _pixels - minScrollExtent;
     double afterExtent = maxScrollExtent - _pixels;
     if (insideExtent > 0.0) {
-      return new ScrollableMetrics(
+      return new ScrollMetrics(
         extentBefore: physics.extentMultiplier * beforeExtent / insideExtent,
         extentInside: physics.extentMultiplier,
         extentAfter: physics.extentMultiplier * afterExtent / insideExtent,
         viewportDimension: viewportDimension,
       );
     } else {
-      return new ScrollableMetrics(
+      return new ScrollMetrics(
         extentBefore: 0.0,
         extentInside: 0.0,
         extentAfter: 0.0,