Regression “Null check operator used on a null value” thrown by LayoutBuilder #168936
Description
Steps to reproduce
- Run the minimal reproducible sample on the current master channel.
- Wait ~1 – 2 s – the app crashes with the error
"Null check operator used on a null value" coming from LayoutBuilder.
Expected results
The sample should run without errors.
Actual results
"Null check operator used on a null value” exceptions are thrown permanently.
Regression details:
First bad commit: merge of PR #154681 – “Make sure LayoutBuilder rebuild in an inactive route” (28 Mar 2025).
git bisect confirms that the crash is introduced by this PR.
@LongCatIsLooong
Code sample
Code sample
I rebuilt the key parts of our app’s complex widget hierarchy in this sample; the structure is deliberate, because simpler layouts don’t trigger the bug.
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
void main() {
runApp(
CupertinoApp(
home: CupertinoPageScaffold(
navigationBar: CupertinoNavigationBar(
middle: Text('LayoutBuilder issue'),
),
child: TestWidget(),
),
),
);
}
class TestWidget extends StatefulWidget {
@override
State<TestWidget> createState() => _TestWidgetState();
}
class _TestWidgetState extends State<TestWidget>
with SingleTickerProviderStateMixin, AutomaticKeepAliveClientMixin {
late final AnimationController _controller;
late final Animation<double> _height;
@override
void initState() {
super.initState();
_controller = AnimationController(
vsync: this,
duration: const Duration(seconds: 2),
);
_height = Tween<double>(
begin: 0.1,
end: 0.5,
).animate(CurvedAnimation(parent: _controller, curve: Curves.easeInOut));
_controller.repeat(reverse: true);
}
@override
void dispose() {
_controller.dispose();
super.dispose();
}
@override
Widget build(BuildContext context) {
super.build(context);
return AnimatedBuilder(
animation: _height,
builder: (context, child) {
return FractionallySizedBox(
heightFactor: _height.value,
child: CustomScrollView(
slivers: [
SliverList(
delegate: SliverChildListDelegate([TestChild(), TestChild()]),
),
],
),
);
},
);
}
@override
bool get wantKeepAlive => true;
}
class TestChild extends StatefulWidget {
@override
State<TestChild> createState() => _TestChildState();
}
class _TestChildState extends State<TestChild>
with AutomaticKeepAliveClientMixin {
@override
bool get wantKeepAlive => true;
@override
Widget build(BuildContext context) {
super.build(context);
return Column(
children: [
Container(
height: 500,
child: LayoutBuilder(
builder: (context, constraints) {
return Container(color: Colors.red, width: double.infinity);
},
),
),
],
);
}
}
Screenshots or Video
Logs
Logs
════════ Exception caught by rendering library ═════════════════════════════════
The following _TypeError was thrown during performLayout():
Null check operator used on a null value
The relevant error-causing widget was:
LayoutBuilder LayoutBuilder:file:///Users/xxx/Desktop/layout_builder_issue/lib/main.dart:91:18
When the exception was thrown, this was the stack:
#0 RenderObject.layout (package:flutter/src/rendering/object.dart:2716:96)
object.dart:2716
#1 _RenderLayoutBuilder.performLayout (package:flutter/src/widgets/layout_builder.dart:440:14)
layout_builder.dart:440
#2 RenderObject._layoutWithoutResize (package:flutter/src/rendering/object.dart:2627:7)
object.dart:2627
#3 PipelineOwner.flushLayout (package:flutter/src/rendering/object.dart:1145:18)
object.dart:1145
#4 PipelineOwner.flushLayout (package:flutter/src/rendering/object.dart:1158:15)
object.dart:1158
#5 RendererBinding.drawFrame (package:flutter/src/rendering/binding.dart:629:23)
binding.dart:629
#6 WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:1231:13)
binding.dart:1231
#7 RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:495:5)
binding.dart:495
#8 SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:1438:15)
binding.dart:1438
#9 SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:1351:9)
binding.dart:1351
#10 SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:1204:5)
binding.dart:1204
#11 _invoke (dart:ui/hooks.dart:331:13)
hooks.dart:331
#12 PlatformDispatcher._drawFrame (dart:ui/platform_dispatcher.dart:444:5)
platform_dispatcher.dart:444
#13 _drawFrame (dart:ui/hooks.dart:303:31)
hooks.dart:303
The following RenderObject was being processed when the exception was fired: _RenderLayoutBuilder#c6cb0 NEEDS-LAYOUT NEEDS-PAINT
parentData: <none> (can use size)
constraints: BoxConstraints(0.0<=w<=440.0, h=500.0)
size: Size(440.0, 500.0)
child: RenderConstrainedBox#52f91 NEEDS-PAINT
parentData: offset=Offset(0.0, 0.0) (can use size)
constraints: BoxConstraints(0.0<=w<=440.0, h=500.0)
size: Size(440.0, 500.0)
additionalConstraints: BoxConstraints(w=Infinity, 0.0<=h<=Infinity)
child: _RenderColoredBox#6bdaa NEEDS-PAINT
parentData: <none> (can use size)
constraints: BoxConstraints(w=440.0, h=500.0)
size: Size(440.0, 500.0)
behavior: opaque
child: RenderLimitedBox#6da64 NEEDS-PAINT
parentData: <none> (can use size)
constraints: BoxConstraints(w=440.0, h=500.0)
size: Size(440.0, 500.0)
maxWidth: 0.0
maxHeight: 0.0
child: RenderConstrainedBox#e6ea7 NEEDS-PAINT
parentData: <none> (can use size)
constraints: BoxConstraints(w=440.0, h=500.0)
size: Size(440.0, 500.0)
additionalConstraints: BoxConstraints(biggest)
RenderObject: _RenderLayoutBuilder#c6cb0 NEEDS-LAYOUT NEEDS-PAINT
parentData: <none> (can use size)
constraints: BoxConstraints(0.0<=w<=440.0, h=500.0)
size: Size(440.0, 500.0)
child: RenderConstrainedBox#52f91 NEEDS-PAINT
parentData: offset=Offset(0.0, 0.0) (can use size)
constraints: BoxConstraints(0.0<=w<=440.0, h=500.0)
size: Size(440.0, 500.0)
additionalConstraints: BoxConstraints(w=Infinity, 0.0<=h<=Infinity)
child: _RenderColoredBox#6bdaa NEEDS-PAINT
parentData: <none> (can use size)
constraints: BoxConstraints(w=440.0, h=500.0)
size: Size(440.0, 500.0)
behavior: opaque
child: RenderLimitedBox#6da64 NEEDS-PAINT
parentData: <none> (can use size)
constraints: BoxConstraints(w=440.0, h=500.0)
size: Size(440.0, 500.0)
maxWidth: 0.0
maxHeight: 0.0
child: RenderConstrainedBox#e6ea7 NEEDS-PAINT
parentData: <none> (can use size)
constraints: BoxConstraints(w=440.0, h=500.0)
size: Size(440.0, 500.0)
additionalConstraints: BoxConstraints(biggest)Flutter Doctor output
Doctor output
Flutter 3.33.0-1.0.pre.78 • channel master • https://github.com/flutter/flutter.git
Framework • revision 773d076621 (21 hours ago) • 2025-05-14 15:59:14 -0700
Engine • revision 773d076621 (21 hours ago) • 2025-05-14 15:59:14 -0700
Tools • Dart 3.9.0 (build 3.9.0-117.0.dev) • DevTools 2.46.0