Fix SliverMainAxisGroup scrollOffsetCorrection #174369
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This pull request fixes an issue where SliverMainAxisGroup did not correctly handle scrollOffsetCorrection from its children. The change adds logic to RenderSliverMainAxisGroup to check for and propagate this correction, which is the correct approach. A comprehensive regression test has been added to verify the fix in a scenario with a dynamically changing list. My review focuses on improving the new test's maintainability by addressing code duplication and inconsistency.
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| testWidgets( | ||
| 'With SliverList can handle inaccurate scroll offset due to changes in children list', | ||
| (WidgetTester tester) async { | ||
| bool skip = true; | ||
| Widget buildItem(BuildContext context, int index) { | ||
| return !skip || index.isEven | ||
| ? Card( | ||
| child: ListTile(title: Text('item$index', style: const TextStyle(fontSize: 80))), | ||
| ) | ||
| : Container(); | ||
| } | ||
|
|
||
| await tester.pumpWidget( | ||
| MaterialApp( | ||
| theme: ThemeData(useMaterial3: false), | ||
| home: Scaffold( | ||
| body: CustomScrollView( | ||
| slivers: <Widget>[ | ||
| SliverMainAxisGroup( | ||
| slivers: <Widget>[ | ||
| SliverList(delegate: SliverChildBuilderDelegate(buildItem, childCount: 30)), | ||
| ], | ||
| ), | ||
| ], | ||
| ), | ||
| ), | ||
| ), | ||
| ); | ||
| // Only even items 0~12 are on the screen. | ||
| expect(find.text('item0'), findsOneWidget); | ||
| expect(find.text('item12'), findsOneWidget); | ||
| expect(find.text('item14'), findsNothing); | ||
|
|
||
| await tester.drag(find.byType(CustomScrollView), const Offset(0.0, -750.0)); | ||
| await tester.pump(); | ||
| // Only even items 16~28 are on the screen. | ||
| expect(find.text('item15'), findsNothing); | ||
| expect(find.text('item16'), findsOneWidget); | ||
| expect(find.text('item28'), findsOneWidget); | ||
|
|
||
| skip = false; | ||
| await tester.pumpWidget( | ||
| MaterialApp( | ||
| home: Scaffold( | ||
| body: CustomScrollView( | ||
| slivers: <Widget>[ | ||
| SliverMainAxisGroup( | ||
| slivers: <Widget>[ | ||
| SliverList(delegate: SliverChildBuilderDelegate(buildItem, childCount: 30)), | ||
| ], | ||
| ), | ||
| ], | ||
| ), | ||
| ), | ||
| ), | ||
| ); | ||
|
|
||
| // Only items 12~19 are on the screen. | ||
| expect(find.text('item11'), findsNothing); | ||
| expect(find.text('item12'), findsOneWidget); | ||
| expect(find.text('item19'), findsOneWidget); | ||
| expect(find.text('item20'), findsNothing); | ||
|
|
||
| await tester.drag(find.byType(CustomScrollView), const Offset(0.0, 250.0)); | ||
| await tester.pump(); | ||
|
|
||
| // Only items 10~16 are on the screen. | ||
| expect(find.text('item9'), findsNothing); | ||
| expect(find.text('item10'), findsOneWidget); | ||
| expect(find.text('item16'), findsOneWidget); | ||
| expect(find.text('item17'), findsNothing); | ||
|
|
||
| // The inaccurate scroll offset should reach zero at this point | ||
| await tester.drag(find.byType(CustomScrollView), const Offset(0.0, 250.0)); | ||
| await tester.pump(); | ||
|
|
||
| // Only items 7~13 are on the screen. | ||
| expect(find.text('item6'), findsNothing); | ||
| expect(find.text('item7'), findsOneWidget); | ||
| expect(find.text('item13'), findsOneWidget); | ||
| expect(find.text('item14'), findsNothing); | ||
|
|
||
| // It will be corrected as we scroll, so we have to drag multiple times. | ||
| await tester.drag(find.byType(CustomScrollView), const Offset(0.0, 250.0)); | ||
| await tester.pump(); | ||
| await tester.drag(find.byType(CustomScrollView), const Offset(0.0, 250.0)); | ||
| await tester.pump(); | ||
| await tester.drag(find.byType(CustomScrollView), const Offset(0.0, 250.0)); | ||
| await tester.pump(); | ||
|
|
||
| // Only items 0~6 are on the screen. | ||
| expect(find.text('item0'), findsOneWidget); | ||
| expect(find.text('item6'), findsOneWidget); | ||
| expect(find.text('item7'), findsNothing); | ||
| }, | ||
| ); |
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The MaterialApp widget is constructed twice in this test, and the two instances are inconsistent as the second one (line 1243) is missing the theme property. This could lead to subtle differences in widget sizes, making the test less reliable.1
To improve readability, reduce duplication, and ensure consistency, consider extracting the widget creation into a local helper function.
For example:
Widget buildFrame() {
return MaterialApp(
theme: ThemeData(useMaterial3: false),
home: Scaffold(
body: CustomScrollView(
slivers: <Widget>[
SliverMainAxisGroup(
slivers: <Widget>[
SliverList(delegate: SliverChildBuilderDelegate(buildItem, childCount: 30)),
],
),
],
),
),
);
}
await tester.pumpWidget(buildFrame());
// ...
skip = false;
await tester.pumpWidget(buildFrame());Style Guide References
Footnotes
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That's not a bad point. Are the two pumpWidgets sections of the test self contained too? Maybe you could split it into two separate tests.
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Both calls of tester.pumpWidget in same test are necessary to update the widgets tree with skip=true/false that trigger a SliverGeometry.scrollOffsetCorrection and thus reproduce the issue.
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@justinmc, , can I resolve this ? As mentioned before, both calls to tester.pumpWidget are necessary in this test. The second call uses the skip variable to modify the SliverList state, which is precisely what triggers the SliverGeometry.scrollOffsetCorrection we need to verify.
|
@Piinks Tagged you for review since this is about Slivers. I also plan to take a look. |
justinmc
reviewed
Aug 26, 2025
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| // Only even items 0~12 are on the screen. | ||
| expect(find.text('item0'), findsOneWidget); | ||
| expect(find.text('item12'), findsOneWidget); | ||
| expect(find.text('item14'), findsNothing); |
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Nit: You could loop through 0-12 if you think it would be valuable to check everything.
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Hi @justinmc, thanks for your review. FYI, this test is a duplicate of "slivers_test.dart" -> "SliverList can handle inaccurate scroll offset due to changes in children list".
I modified the test with a loop, as you suggested.
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Is it ok for you @justinmc ?
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to
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| testWidgets( | ||
| 'With SliverList can handle inaccurate scroll offset due to changes in children list', | ||
| (WidgetTester tester) async { | ||
| bool skip = true; | ||
| Widget buildItem(BuildContext context, int index) { | ||
| return !skip || index.isEven | ||
| ? Card( | ||
| child: ListTile(title: Text('item$index', style: const TextStyle(fontSize: 80))), | ||
| ) | ||
| : Container(); | ||
| } | ||
|
|
||
| await tester.pumpWidget( | ||
| MaterialApp( | ||
| theme: ThemeData(useMaterial3: false), | ||
| home: Scaffold( | ||
| body: CustomScrollView( | ||
| slivers: <Widget>[ | ||
| SliverMainAxisGroup( | ||
| slivers: <Widget>[ | ||
| SliverList(delegate: SliverChildBuilderDelegate(buildItem, childCount: 30)), | ||
| ], | ||
| ), | ||
| ], | ||
| ), | ||
| ), | ||
| ), | ||
| ); | ||
| // Only even items 0~12 are on the screen. | ||
| expect(find.text('item0'), findsOneWidget); | ||
| expect(find.text('item12'), findsOneWidget); | ||
| expect(find.text('item14'), findsNothing); | ||
|
|
||
| await tester.drag(find.byType(CustomScrollView), const Offset(0.0, -750.0)); | ||
| await tester.pump(); | ||
| // Only even items 16~28 are on the screen. | ||
| expect(find.text('item15'), findsNothing); | ||
| expect(find.text('item16'), findsOneWidget); | ||
| expect(find.text('item28'), findsOneWidget); | ||
|
|
||
| skip = false; | ||
| await tester.pumpWidget( | ||
| MaterialApp( | ||
| home: Scaffold( | ||
| body: CustomScrollView( | ||
| slivers: <Widget>[ | ||
| SliverMainAxisGroup( | ||
| slivers: <Widget>[ | ||
| SliverList(delegate: SliverChildBuilderDelegate(buildItem, childCount: 30)), | ||
| ], | ||
| ), | ||
| ], | ||
| ), | ||
| ), | ||
| ), | ||
| ); | ||
|
|
||
| // Only items 12~19 are on the screen. | ||
| expect(find.text('item11'), findsNothing); | ||
| expect(find.text('item12'), findsOneWidget); | ||
| expect(find.text('item19'), findsOneWidget); | ||
| expect(find.text('item20'), findsNothing); | ||
|
|
||
| await tester.drag(find.byType(CustomScrollView), const Offset(0.0, 250.0)); | ||
| await tester.pump(); | ||
|
|
||
| // Only items 10~16 are on the screen. | ||
| expect(find.text('item9'), findsNothing); | ||
| expect(find.text('item10'), findsOneWidget); | ||
| expect(find.text('item16'), findsOneWidget); | ||
| expect(find.text('item17'), findsNothing); | ||
|
|
||
| // The inaccurate scroll offset should reach zero at this point | ||
| await tester.drag(find.byType(CustomScrollView), const Offset(0.0, 250.0)); | ||
| await tester.pump(); | ||
|
|
||
| // Only items 7~13 are on the screen. | ||
| expect(find.text('item6'), findsNothing); | ||
| expect(find.text('item7'), findsOneWidget); | ||
| expect(find.text('item13'), findsOneWidget); | ||
| expect(find.text('item14'), findsNothing); | ||
|
|
||
| // It will be corrected as we scroll, so we have to drag multiple times. | ||
| await tester.drag(find.byType(CustomScrollView), const Offset(0.0, 250.0)); | ||
| await tester.pump(); | ||
| await tester.drag(find.byType(CustomScrollView), const Offset(0.0, 250.0)); | ||
| await tester.pump(); | ||
| await tester.drag(find.byType(CustomScrollView), const Offset(0.0, 250.0)); | ||
| await tester.pump(); | ||
|
|
||
| // Only items 0~6 are on the screen. | ||
| expect(find.text('item0'), findsOneWidget); | ||
| expect(find.text('item6'), findsOneWidget); | ||
| expect(find.text('item7'), findsNothing); | ||
| }, | ||
| ); |
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That's not a bad point. Are the two pumpWidgets sections of the test self contained too? Maybe you could split it into two separate tests.
| @@ -1197,6 +1197,103 @@ void main() { | |||
| expect(tester.getBottomRight(find.byKey(key)), offset - const Offset(0.0, 20.0)); | |||
| }, | |||
| ); | |||
|
|
|||
| testWidgets( | |||
| 'With SliverList can handle inaccurate scroll offset due to changes in children list', | |||
There was a problem hiding this comment.
I confirmed that this test fails on master.
| if (childLayoutGeometry case SliverGeometry( | ||
| :final double scrollOffsetCorrection, | ||
| ) when scrollOffsetCorrection != 0) { | ||
| geometry = SliverGeometry(scrollOffsetCorrection: scrollOffsetCorrection); |
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I'll defer to @Piinks on whether this is the right way to solve this.
Piinks
reviewed
Aug 28, 2025
Comment on lines
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to
333
| if (childLayoutGeometry case SliverGeometry( | ||
| :final double scrollOffsetCorrection, | ||
| ) when scrollOffsetCorrection != 0) { |
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Can you write this differently? We have not adopted this pattern in the framework because it can be hard for readability in some cases.
Piinks
approved these changes
Sep 5, 2025
|
There are some merge conflicts that need to be resolved here, and then this should be good to go! |
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Fixes : #174368
Pre-launch Checklist
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