Error while modifying Widget Preview annotations #173710
Description
Steps to reproduce
Unfortunately I don't know exactly what I typed that triggered this because I didn't notice it had crashed initially, but I'll post a comment on this issue if I figure out the steps.
Edit: I repro'd it.. it was when I added a non-const wrapper function:
@Preview(name: 'Test Preview 4', wrapper: Directionality(textDirection: TextDirection.rtl, child: w))cc @bkonyi
Expected results
No crash, preview process keeps running.
Actual results
The preview stopped updating and I noticed the an exception log was written and noted in the process output.
Code sample
Code sample
import 'package:flutter/material.dart';
import 'package:flutter/widget_previews.dart';
import 'package:flutter_counter/my_app.dart';
import 'package:http/http.dart';
void main() {
runApp(const MyApp9());
}
class MyHomePage extends StatefulWidget {
@Preview(name: 'Test Preview 4', wrapper: Directionality(textDirection: TextDirection.rtl, child: w))
const MyHomePage.preview({Key? key}) : this(key: key, title: 'Test Preview');
const MyHomePage({super.key, required this.title});
final String title;
@override
State<MyHomePage> createState() {
return _MyHomePageState();
} //
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
void _incrementCounter() {
//
// get(Uri.parse('https://www.google.co.uk/'));
setState(() {
_counter++;
_counter++;
});
}
@override
Widget build(BuildContext context) {
debugPrint('test');
debugPrint('test');
return Scaffold(
appBar: AppBar(
backgroundColor: Theme.of(context).colorScheme.inversePrimary,
title: Text(widget.title),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'You have pushed the button this many times:',
// style: Theme.of(context).textTheme.headlineMedium,
),
Padding(
padding: const EdgeInsets.all(8.0),
child: Text(
'$_counter',
style: Theme.of(context).textTheme.headlineMedium,
),
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: const Icon(Icons.add),
),
);
}
}
void f2(
({
int myInt,
}) r) {
if (r case (:var myInt)) {
print(myInt);
}
}Screenshots or Video
Screenshots / Video demonstration
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Logs
Logs
command
flutter widget-preview start --machine --web-server
exception
_TypeError: Null check operator used on a null value
#0 _PreviewVisitor.visitAnnotation (package:flutter_tools/src/widget_preview/dependency_graph.dart:85:75)
#1 AnnotationImpl.accept (package:analyzer/src/dart/ast/ast.dart:366:50)
#2 NodeListImpl.accept (package:analyzer/src/dart/ast/ast.dart:13243:20)
#3 _AnnotatedNodeMixin._visitCommentAndAnnotations (package:analyzer/src/dart/ast/ast.dart:19496:17)
#4 AnnotatedNodeImpl.visitChildren (package:analyzer/src/dart/ast/ast.dart:165:5)
#5 ConstructorDeclarationImpl.visitChildren (package:analyzer/src/dart/ast/ast.dart:4349:11)
#6 _PreviewVisitor._scopedVisitChildren (package:flutter_tools/src/widget_preview/dependency_graph.dart:130:10)
#7 _PreviewVisitor.visitConstructorDeclaration (package:flutter_tools/src/widget_preview/dependency_graph.dart:67:5)
#8 ConstructorDeclarationImpl.accept (package:analyzer/src/dart/ast/ast.dart:4345:15)
#9 NodeListImpl.accept (package:analyzer/src/dart/ast/ast.dart:13243:20)
#10 ClassDeclarationImpl.visitChildren (package:analyzer/src/dart/ast/ast.dart:2945:13)
#11 RecursiveAstVisitor.visitClassDeclaration (package:analyzer/dart/ast/visitor.dart:940:10)
#12 ClassDeclarationImpl.accept (package:analyzer/src/dart/ast/ast.dart:2935:50)
#13 NodeListImpl.accept (package:analyzer/src/dart/ast/ast.dart:13243:20)
#14 CompilationUnitImpl.visitChildren (package:analyzer/src/dart/ast/ast.dart:3611:21)
#15 LibraryPreviewNode.findPreviews (package:flutter_tools/src/widget_preview/dependency_graph.dart:195:20)
#16 PreviewDetector._findPreviewFunctions (package:flutter_tools/src/widget_preview/preview_detector.dart:217:30)
<asynchronous suspension>
#17 PreviewDetector._fileAddedOrUpdated (package:flutter_tools/src/widget_preview/preview_detector.dart:143:56)
<asynchronous suspension>
#18 PreviewDetector._onFileSystemEvent.<anonymous closure> (package:flutter_tools/src/widget_preview/preview_detector.dart:122:9)
<asynchronous suspension>
#19 PreviewDetectorMutex.runGuarded (package:flutter_tools/src/widget_preview/utils.dart:100:14)
<asynchronous suspension>
#20 PreviewDetector._onFileSystemEvent (package:flutter_tools/src/widget_preview/preview_detector.dart:81:5)
<asynchronous suspension>
Flutter Doctor output
Doctor output
[!] Flutter (Channel [user-branch], 3.33.0-1.0.pre-1371, on Microsoft Windows [Version 10.0.26100.4652], locale en-GB) [196ms]
! Flutter version 3.33.0-1.0.pre-1371 on channel [user-branch] at D:\Dev\Google\Flutter\Flutter main
Currently on an unknown channel. Run `flutter channel` to switch to an official channel.
If that doesn't fix the issue, reinstall Flutter by following instructions at https://flutter.dev/setup.
! Warning: `dart` on your path resolves to D:\Tools\Dart\Stable\bin\dart.exe, which is not inside your current Flutter SDK checkout at D:\Dev\Google\Flutter\Flutter main. Consider adding D:\Dev\Google\Flutter\Flutter main\bin to the front of your path.
! Upstream repository unknown source is not a standard remote.
Set environment variable "FLUTTER_GIT_URL" to unknown source to dismiss this error.
• Framework revision ac43d96b78 (16 hours ago), 2025-08-12 17:34:27 -0400
• Engine revision b0c8612eda
• Dart version 3.10.0 (build 3.10.0-88.0.dev)
• DevTools version 2.49.0
• Feature flags: enable-web, enable-linux-desktop, enable-macos-desktop, enable-windows-desktop, enable-android, enable-ios, cli-animations, enable-native-assets, enable-lldb-debugging
• If those were intentional, you can disregard the above warnings; however it is recommended to use "git" directly to perform update checks and upgrades.
[✓] Windows Version (11 Pro 64-bit, 24H2, 2009) [3.7s]
[!] Android toolchain - develop for Android devices (Android SDK version 35.0.0) [2.8s]
• Android SDK at C:\Users\danny\AppData\Local\Android\sdk
• Emulator version 35.4.9.0 (build_id 13025442) (CL:N/A)
• Platform android-36, build-tools 35.0.0
• Java binary at: C:\Program Files\Android\Android Studio\jbr\bin\java
This is the JDK bundled with the latest Android Studio installation on this machine.
To manually set the JDK path, use: `flutter config --jdk-dir="path/to/jdk"`.
• Java version OpenJDK Runtime Environment (build 21.0.6+-13355223-b631.42)
! Some Android licenses not accepted. To resolve this, run: flutter doctor --android-licenses
[✓] Chrome - develop for the web [49ms]
• Chrome at C:\Program Files\Google\Chrome\Application\chrome.exe
[✓] Visual Studio - develop Windows apps (Visual Studio Community 2022 17.10.5) [48ms]
• Visual Studio at C:\Program Files\Microsoft Visual Studio\2022\Community
• Visual Studio Community 2022 version 17.10.35122.118
• Windows 10 SDK version 10.0.26100.0
[✓] Connected device (3 available) [402ms]
• Windows (desktop) • windows • windows-x64 • Microsoft Windows [Version 10.0.26100.4652]
• Chrome (web) • chrome • web-javascript • Google Chrome 139.0.7258.67
• Edge (web) • edge • web-javascript • Microsoft Edge 138.0.3351.77
[✓] Network resources [363ms]
• All expected network resources are available.
! Doctor found issues in 2 categories.