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fix(flutter_todos): fix zone mismatch error #4225

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Aug 27, 2024
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fix(flutter_todos): fix zone mismatch error #4225

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12 changes: 7 additions & 5 deletions examples/flutter_todos/lib/bootstrap.dart
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Original file line number Diff line number Diff line change
@@ -1,7 +1,7 @@
import 'dart:async';
import 'dart:developer';

import 'package:bloc/bloc.dart';
import 'package:flutter/foundation.dart';
import 'package:flutter/widgets.dart';
import 'package:flutter_todos/app/app.dart';
import 'package:flutter_todos/app/app_bloc_observer.dart';
Expand All @@ -13,12 +13,14 @@ void bootstrap({required TodosApi todosApi}) {
log(details.exceptionAsString(), stackTrace: details.stack);
};

PlatformDispatcher.instance.onError = (error, stack) {
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Can you elaborate a bit regarding the advantage of using PlatformDispatcher instead of wrapping runApp in a guarded zone?

Also we should probably using the WidgetsBinding to access the platform dispatcher instance as per:

Consider avoiding static references to this singleton through PlatformDispatcher.instance and instead prefer using a binding for dependency resolution such as WidgetsBinding.instance.platformDispatcher. See PlatformDispatcher.instance for more information about why this is preferred.

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@LukasMirbt LukasMirbt Aug 15, 2024 •
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Hi!

Yea, sure!

The reason I opened this PR is because I got the following error in the console when running the flutter_todos example:

Zone mismatch.
The Flutter bindings were initialized in a different zone than is now being used. This will likely cause confusion and bugs as any zone-specific configuration will inconsistently use the configuration of the original binding initialization zone or this zone based on hard-to-predict factors such as which zone was active when a particular callback was set.
It is important to use the same zone when calling ensureInitialized on the binding as when calling runApp later.
To make this warning fatal, set BindingBase.debugZoneErrorsAreFatal to true before the bindings are initialized (i.e. as the first statement in void main() { }).

The migration guide for this error in the Flutter documentation suggests that

The best way to silence this message is to remove use of Zones from within the application.

(I also couldn't find any way to make the error go away and keep runZonedGuarded).

Also we should probably using the WidgetsBinding to access the platform dispatcher instance as per:

I based the PR on the following snippet from the Handling errors in Flutter documentation:

import 'package:flutter/material.dart';
import 'dart:ui';

void main() {
  MyBackend myBackend = MyBackend();
  PlatformDispatcher.instance.onError = (error, stack) {
    myBackend.sendError(error, stack);
    return true;
  };
  runApp(const MyApp());
}

Consider avoiding static references to this singleton through PlatformDispatcher.instance and instead prefer using a binding for dependency resolution such as WidgetsBinding.instance.platformDispatcher. See PlatformDispatcher.instance for more information about why this is preferred.

The same documentation mentions that

The only place that WidgetsBinding.instance.platformDispatcher is inappropriate is if access to these APIs is required before the binding is initialized by invoking runApp() or WidgetsFlutterBinding.instance.ensureInitialized(). In that case, it is necessary (though unfortunate) to use the PlatformDispatcher.instance object statically.

so it might make sense to use PlatformDispatcher.instance directly if we don't also want to add WidgetsFlutterBinding.instance.ensureInitialized().

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The reason I opened this PR is because I got the following error in the console when running the flutter_todos example

You just ran the example with no changes and saw the error? I'll try to see if I can reproduce, thanks for the context!

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Can confirm that I'm still seeing this error on Flutter 3.24.1 on multiple platforms

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Thanks I'll review this later today, apologies for the delay!

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@felangel felangel Aug 25, 2024 •
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@LukasMirbt what platforms are you seeing this on? I've tested using Flutter 3.24.1 on iOS, Android, and Web and am not seeing any errors

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To clarify, it's a warning - not an error. The app still runs and behaves normally but the warning below can be seen in the console (you may have to scroll up a bit).

I was able to reproduce this on iOS, Android and web on different machines.

It's worth noting that I also get another error first when running the example:

Error (Xcode): ../../../../.pub-cache/hosted/pub.dev/win32-5.2.0/lib/src/guid.dart:32:9: Error: Type 'UnmodifiableUint8ListView' not found.

Which I solve with
flutter pub upgrade

Zone mismatch.
      The Flutter bindings were initialized in a different zone than is now being used. This will likely cause confusion and bugs as any zone-specific configuration will inconsistently use the configuration of the original binding initialization zone or this zone based on hard-to-predict factors such as which zone was active when a particular callback was set.
      It is important to use the same zone when calling `ensureInitialized` on the binding as when calling `runApp` later.
      To make this warning fatal, set BindingBase.debugZoneErrorsAreFatal to true before the bindings are initialized (i.e. as the first statement in `void main() { }`).
[log] #0      BindingBase.debugCheckZone.<anonymous closure> (package:flutter/src/foundation/binding.dart:504:29)
      #1      BindingBase.debugCheckZone (package:flutter/src/foundation/binding.dart:509:6)
binding.dart:509
      #2      _runWidget (package:flutter/src/widgets/binding.dart:1463:18)
binding.dart:1463
      #3      runApp (package:flutter/src/widgets/binding.dart:1399:3)
binding.dart:1399
      #4      bootstrap.<anonymous closure> (package:flutter_todos/bootstrap.dart:21:11)
bootstrap.dart:21
      #5      _rootRun (dart:async/zone.dart:1399:13)
zone.dart:1399
      #6      _CustomZone.run (dart:async/zone.dart:1301:19)
zone.dart:1301

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I ran pub upgrade to resolve the win32 issue but don't see any Zone mismatch error 🤔

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It's fine either way I'll get this merged shortly, thanks!

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I ran pub upgrade to resolve the win32 issue but don't see any Zone mismatch error 🤔

Strange 🤔

It's fine either way I'll get this merged shortly, thanks!

Alright, no problem! 👍

log(error.toString(), stackTrace: stack);
return true;
};

Bloc.observer = const AppBlocObserver();

final todosRepository = TodosRepository(todosApi: todosApi);

runZonedGuarded(
() => runApp(App(todosRepository: todosRepository)),
(error, stackTrace) => log(error.toString(), stackTrace: stackTrace),
);
runApp(App(todosRepository: todosRepository));
}