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Fix overscroll edge case that puts NestedScrollViews out of sync (#68644)

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Kate Lovett 2020-10-22 15:37:06 -07:00 committed by GitHub
parent c5c2b24a07
commit 8e8f61856a
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2 changed files with 58 additions and 1 deletions
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4
packages/flutter/lib/src/widgets/nested_scroll_view.dart
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@ -1343,7 +1343,9 @@ class _NestedScrollPosition extends ScrollPosition implements ScrollActivityDele
// The logic for max is equivalent but on the other side.
final double max = delta > 0.0
? double.infinity
: math.max(maxScrollExtent, pixels);
// If pixels < 0.0, then we are currently in overscroll. The max should be
// 0.0, representing the end of the overscrolled portion.
: pixels < 0.0 ? 0.0 : math.max(maxScrollExtent, pixels);
final double oldPixels = pixels;
final double newPixels = (pixels - delta).clamp(min, max);
final double clampedDelta = newPixels - pixels;

55
packages/flutter/test/widgets/nested_scroll_view_test.dart
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@ -1906,6 +1906,61 @@ void main() {
expect(tester.getCenter(find.text('Item 49')).dy, equals(585.0));
}, variant: const TargetPlatformVariant(<TargetPlatform>{ TargetPlatform.iOS }));
});
// Regression test for https://github.com/flutter/flutter/issues/63978
testWidgets('Inner _NestedScrollPosition.applyClampedDragUpdate correctly calculates range when in overscroll', (WidgetTester tester) async {
final GlobalKey<NestedScrollViewState> nestedScrollView = GlobalKey();
await tester.pumpWidget(MaterialApp(
home: Scaffold(
body: NestedScrollView(
key: nestedScrollView,
headerSliverBuilder: (BuildContext context, bool boxIsScrolled) {
return <Widget>[
const SliverAppBar(
expandedHeight: 200,
title: Text('Test'),
)
];
},
body: ListView.builder(
itemExtent: 100.0,
itemBuilder: (BuildContext context, int index) => Container(
padding: const EdgeInsets.all(10.0),
child: Material(
color: index.isEven ? Colors.cyan : Colors.deepOrange,
child: Center(
child: Text(index.toString()),
),
),
),
),
),
),
));
expect(nestedScrollView.currentState!.outerController.position.pixels, 0.0);
expect(nestedScrollView.currentState!.innerController.position.pixels, 0.0);
expect(nestedScrollView.currentState!.outerController.position.maxScrollExtent, 200.0);
final Offset point = tester.getCenter(find.text('1'));
// Drag slightly into overscroll in the inner position.
final TestGesture gesture = await tester.startGesture(point);
await gesture.moveBy(const Offset(0.0, 5.0));
await tester.pump();
expect(nestedScrollView.currentState!.outerController.position.pixels, 0.0);
expect(nestedScrollView.currentState!.innerController.position.pixels, -5.0);
// Move by a much larger delta than the amount of over scroll, in a very
// short period of time.
await gesture.moveBy(const Offset(0.0, -500.0));
await tester.pump();
// The overscrolled inner position should have closed, then passed the
// correct remaining delta to the outer position, and finally any remainder
// back to the inner position.
expect(
nestedScrollView.currentState!.outerController.position.pixels,
nestedScrollView.currentState!.outerController.position.maxScrollExtent,
);
expect(nestedScrollView.currentState!.innerController.position.pixels, 295.0);
}, variant: const TargetPlatformVariant(<TargetPlatform>{ TargetPlatform.iOS, TargetPlatform.macOS }));
}
class TestHeader extends SliverPersistentHeaderDelegate {