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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
Activity
danagbemava-nc commentedon May 16, 2025
Reproducible using the code sample provided above. Can confirm that this works as expected on the stable branch but not the beta or master branches.
flutter doctor -v
faisalansari0367 commentedon May 21, 2025
Even when the relayoutBoundary is null the else condition is being executed.
Shall we add another check for it?
justinmc commentedon May 21, 2025
@faisalansari0367 Can you link to that code?
I'm also curious what PR broke this if someone can track it down.
b3nni97 commentedon May 22, 2025
@justinmc I have already tracked this back to #154681
faisalansari0367 commentedon May 22, 2025
@b3nni97 Thanks for tracking it.
Any idea what's the cause for it?
OliverNarramore commentedon May 23, 2025
I'm also experiencing this issue on 3.32 (latest stable) it's a blocker for us.
faisalansari0367 commentedon May 28, 2025
final RenderObject relayoutBoundary = isRelayoutBoundary ? this : parent!._relayoutBoundary ?? this;The above fix works but is this correct?
JeromeGsq commentedon Jun 6, 2025
Any news or suggestions on this issue please?
LongCatIsLooong commentedon Jun 6, 2025
Fixed in #169958
blastervla commentedon Jun 13, 2025
Hi. What's the ETA to get this fix to the
stablechannel? I see it merged inmasterbut this is still broken instableLongCatIsLooong commentedon Jun 24, 2025
Created a CP request. IIRC creating cherry picks doesn't require special permissions so you can follow the steps here in the future.
[CP-stable]Make _layoutBoundary a boolean 2 (#171106)
github-actions commentedon Jul 8, 2025
This thread has been automatically locked since there has not been any recent activity after it was closed. If you are still experiencing a similar issue, please open a new bug, including the output of
flutter doctor -vand a minimal reproduction of the issue.