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Fix NestedScrollView inner ballistic activity for 0 velocity (#61386)

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Kate Lovett 2020-07-16 09:41:04 -07:00 committed by GitHub
parent 563afe381c
commit 16d5dd9b13
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2 changed files with 95 additions and 7 deletions
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11
packages/flutter/lib/src/widgets/nested_scroll_view.dart
View File

@ -918,9 +918,7 @@ class _NestedScrollCoordinator implements ScrollActivityDelegate, ScrollHoldCont
ScrollActivity createInnerBallisticScrollActivity(_NestedScrollPosition position, double velocity) {
return position.createBallisticScrollActivity(
position.physics.createBallisticSimulation(
velocity == 0
? position as ScrollMetrics
: _getMetrics(position, velocity),
_getMetrics(position, velocity),
velocity,
),
mode: _NestedBallisticScrollActivityMode.inner,
@ -929,7 +927,8 @@ class _NestedScrollCoordinator implements ScrollActivityDelegate, ScrollHoldCont
_NestedScrollMetrics _getMetrics(_NestedScrollPosition innerPosition, double velocity) {
assert(innerPosition != null);
double pixels, minRange, maxRange, correctionOffset, extra;
double pixels, minRange, maxRange, correctionOffset;
double extra = 0.0;
if (innerPosition.pixels == innerPosition.minScrollExtent) {
pixels = _outerPosition.pixels.clamp(
_outerPosition.minScrollExtent,
@ -939,7 +938,6 @@ class _NestedScrollCoordinator implements ScrollActivityDelegate, ScrollHoldCont
maxRange = _outerPosition.maxScrollExtent;
assert(minRange <= maxRange);
correctionOffset = 0.0;
extra = 0.0;
} else {
assert(innerPosition.pixels != innerPosition.minScrollExtent);
if (innerPosition.pixels < innerPosition.minScrollExtent) {
@ -974,8 +972,7 @@ class _NestedScrollCoordinator implements ScrollActivityDelegate, ScrollHoldCont
if (velocity > 0.0) {
// shrinking
extra = _outerPosition.minScrollExtent - _outerPosition.pixels;
} else {
assert(velocity < 0.0);
} else if (velocity < 0.0) {
// growing
extra = _outerPosition.pixels - (_outerPosition.maxScrollExtent - _outerPosition.minScrollExtent);
}

91
packages/flutter/test/widgets/nested_scroll_view_test.dart
View File

@ -1817,6 +1817,97 @@ void main() {
verifyGeometry(key: appBarKey, paintExtent: 200.0, visible: true);
});
});
group('Correctly handles 0 velocity inner ballistic scroll activity:', () {
// Regression tests for https://github.com/flutter/flutter/issues/17096
Widget _buildBallisticTest(ScrollController controller) {
return MaterialApp(
home: Scaffold(
body: NestedScrollView(
controller: controller,
headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
return <Widget>[
const SliverAppBar(
pinned: true,
expandedHeight: 200.0,
),
];
},
body: ListView.builder(
itemCount: 50,
itemBuilder: (BuildContext context, int index) {
return Container(
child: Padding(
padding: const EdgeInsets.all(8.0),
child: Text('Item $index'),
)
);
}
),
),
),
);
}
testWidgets('overscroll, hold for 0 velocity, and release', (WidgetTester tester) async {
// Dragging into an overscroll and holding so that when released, the
// ballistic scroll activity has a 0 velocity.
final ScrollController controller = ScrollController();
await tester.pumpWidget(_buildBallisticTest(controller));
// Last item of the inner scroll view.
expect(find.text('Item 49'), findsNothing);
// Scroll to bottom
await tester.fling(find.text('Item 3'), const Offset(0.0, -50.0), 10000.0);
await tester.pumpAndSettle();
// End of list
expect(find.text('Item 49'), findsOneWidget);
expect(tester.getCenter(find.text('Item 49')).dy, equals(585.0));
// Overscroll, dragging like this will release with 0 velocity.
await tester.drag(find.text('Item 49'), const Offset(0.0, -50.0));
await tester.pump();
// If handled correctly, the last item should still be visible and
// progressing back down to the bottom edge, instead of jumping further
// up the list and out of view.
expect(find.text('Item 49'), findsOneWidget);
await tester.pumpAndSettle();
expect(tester.getCenter(find.text('Item 49')).dy, equals(585.0));
}, variant: const TargetPlatformVariant(<TargetPlatform>{ TargetPlatform.iOS }));
testWidgets('overscroll, release, and tap', (WidgetTester tester) async {
// Tapping while an inner ballistic scroll activity is in progress will
// trigger a secondary ballistic scroll activity with a 0 velocity.
final ScrollController controller = ScrollController();
await tester.pumpWidget(_buildBallisticTest(controller));
// Last item of the inner scroll view.
expect(find.text('Item 49'), findsNothing);
// Scroll to bottom
await tester.fling(find.text('Item 3'), const Offset(0.0, -50.0), 10000.0);
await tester.pumpAndSettle();
// End of list
expect(find.text('Item 49'), findsOneWidget);
expect(tester.getCenter(find.text('Item 49')).dy, equals(585.0));
// Fling again to trigger first ballistic activity.
await tester.fling(find.text('Item 48'), const Offset(0.0, -50.0), 10000.0);
await tester.pump();
// Tap after releasing the overscroll to trigger secondary inner ballistic
// scroll activity with 0 velocity.
await tester.tap(find.text('Item 49'));
await tester.pumpAndSettle();
// If handled correctly, the ballistic scroll activity should finish
// closing out the overscrolled area, with the last item visible at the
// bottom.
expect(find.text('Item 49'), findsOneWidget);
expect(tester.getCenter(find.text('Item 49')).dy, equals(585.0));
}, variant: const TargetPlatformVariant(<TargetPlatform>{ TargetPlatform.iOS }));
});
}
class TestHeader extends SliverPersistentHeaderDelegate {