SliverVariedExtentList does not respect itemCount when calling itemExtentBuilder #138912
Description
Is there an existing issue for this?
- I have searched the existing issues
- I have read the guide to filing a bug
Steps to reproduce
- Run the example code below.
- It will crash with an out of range error since the itemExtentBuilder is being called in excess of the number of items in the list. Since itemCount is specified, I expect it would not have called for indices outside of that range.
Expected results
App works.
Alternatively, if I try to work around the issue by checking that I am within range, it can lead to other errors like incorrect scroll extent calculations and worse, app hanging. (see second sample)
Actual results
In first sample, app crashes for accessing an index out of range of the list.
In second sample, the app hangs because it is infinitely calling the item extent builder.
Code sample
Code sample 1
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
final List<double> numbers = [
10, 20, 30, 40, 50,
];
@override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
appBar: AppBar(
backgroundColor: Theme.of(context).colorScheme.inversePrimary,
title: const Text('Bug'),
),
body: CustomScrollView(
slivers: [
SliverVariedExtentList.builder(
itemCount: numbers.length,
itemBuilder: (context, index) {
return SizedBox(
height: numbers[index],
child: Text('Size ${numbers[index]}'),
);
},
itemExtentBuilder: (index, dimensions) {
return numbers[index]; // App crashes
},
),
],
),
),
);
}
}
Code sample 2
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
final List<double> numbers = [
10, 20, 30, 40, 50,
];
@override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
appBar: AppBar(
backgroundColor: Theme.of(context).colorScheme.inversePrimary,
title: const Text('Bug'),
),
body: CustomScrollView(
slivers: [
SliverVariedExtentList.builder(
itemCount: numbers.length,
itemBuilder: (context, index) {
return SizedBox(
height: numbers[index],
child: Text('Size ${numbers[index]}'),
);
},
itemExtentBuilder: (index, dimensions) {
if (index >= numbers.length) {
return 0; // App hangs instead of crashing
}
return numbers[index];
},
),
],
),
),
);
}
}
Screenshots or Video
No response
Logs
Logs (from code sample 1 crash scenario)
══╡ EXCEPTION CAUGHT BY RENDERING LIBRARY ╞═════════════════════════════════════════════════════════
The following IndexError was thrown during performLayout():
RangeError (index): Index out of range: index should be less than 5: 5
Widget creation tracking is currently disabled. Enabling it enables improved error messages. It can
be enabled by passing `--track-widget-creation` to `flutter run` or `flutter test`.
When the exception was thrown, this was the stack
The following RenderObject was being processed when the exception was fired: RenderSliverVariedExtentList#0490b relayoutBoundary=up1 NEEDS-LAYOUT NEEDS-PAINT:
creator: SliverVariedExtentList ← Viewport ← IgnorePointer-[GlobalKey#37208] ← Semantics ← Listener
← _GestureSemantics ← RawGestureDetector-[LabeledGlobalKey<RawGestureDetectorState>#e2c18] ←
Listener ← _ScrollableScope ← _ScrollSemantics-[GlobalKey#a52fa] ←
NotificationListener<ScrollMetricsNotification> ← RepaintBoundary ← ⋯
parentData: paintOffset=Offset(0.0, 0.0) (can use size)
constraints: SliverConstraints(AxisDirection.down, GrowthDirection.forward, ScrollDirection.idle,
scrollOffset: 0.0, remainingPaintExtent: 603.0, crossAxisExtent: 641.0, crossAxisDirection:
AxisDirection.right, viewportMainAxisExtent: 603.0, remainingCacheExtent: 853.0, cacheOrigin: 0.0)
geometry: null
no children current live
This RenderObject has no descendants.
════════════════════════════════════════════════════════════════════════════════════════════════════
Another exception was thrown: Unexpected null value.
Another exception was thrown: Unexpected null value.
Another exception was thrown: Unexpected null value.
Another exception was thrown: Unexpected null value.
Another exception was thrown: Unexpected null value.
Another exception was thrown: Unexpected null value.
Another exception was thrown: Unexpected null value.
Another exception was thrown: Unexpected null value.
Another exception was thrown: Unexpected null value.
Another exception was thrown: Unexpected null value.
Another exception was thrown: Unexpected null value.
Another exception was thrown: Unexpected null value.Flutter Doctor output
Doctor output
[✓] Flutter (Channel stable, 3.16.0, on macOS 14.0 23A344 darwin-arm64, locale
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• Flutter version 3.16.0 on channel stable at /Users/katelovett/dev/flutter
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• Java version OpenJDK Runtime Environment (build
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• Java version OpenJDK Runtime Environment (build
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• VS Code at /Applications/Visual Studio Code.app/Contents
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[✓] Connected device (2 available)
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• No issues found!