Unhandled Exception: Invalid argument(s): Illegal argument in isolate message: (object extends NativeWrapper - Library:'dart:ui' Class: Path)

Question

Can anyone tell me whats wrong in this code?

void onPressed() async {
    //Navigator.pushNamed(context, "/screen2", arguments: []);
    var receivePort = ReceivePort();
    await Isolate.spawn(gotoNext, [receivePort.sendPort]);
    final msg = await receivePort.first;
    print(msg);
  }

  void gotoNext(List<dynamic> args) {
    SendPort sendPort = args[0];
    log(args.toString());
    Isolate.exit(sendPort, "OK");
  }

E/flutter (12062): [ERROR:flutter/lib/ui/ui_dart_state.cc(209)] Unhandled Exception: Invalid argument(s): Illegal argument in isolate message: (object extends NativeWrapper - Library:'dart:ui' Class: Path)

Solution

Hii There is a mistake in your code. As far as I know from the official documentation The callback method for an Isolate should be a top level function or a static method. So there are two solution for this problem.

Solution 1. declare callback function as top level function.

class MyHomePage extends StatelessWidget {
  final String title;

  const MyHomePage({Key? key, required this.title}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(child: TextButton(
        child: const Text("Run Isolate"),
        onPressed: _onPressed,
      ));
    );
  }

  // Callback function for Text Button Event this should be a class member
  void _onPressed() async {
    var receivePort = ReceivePort();
    // Here runMyIsolate methos should be a top level function
    await Isolate.spawn(runMyIsolate, [receivePort.sendPort, "My Custom Message"]);
    print(await receivePort.first);
  }
}


// We declare a top level function here for an isolated callback function
void runMyIsolate(List<dynamic> args) {
  var sendPort = args[0] as SendPort;
  print("In runMyIsolate ");
  Isolate.exit(sendPort, args);
}

Solution 2. instead this top level function we can declare this function as a static function for the same class, consider below example.

    class MyHomePage extends StatelessWidget {
  final String title;

  const MyHomePage({Key? key, required this.title}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(child: TextButton(
        child: const Text("Run Isolate"),
        onPressed: _onPressed,
      ));
    );
  }

  // Callback function for Text Button Event this should be a class member
  void _onPressed() async {
    var receivePort = ReceivePort();
    // Here runMyIsolate methos should be a top level function
    await Isolate.spawn(runMyIsolate, [receivePort.sendPort, "My Custom Message"]);
    print(await receivePort.first);
  }
  
  // We declare a static function here for an isolated callback function
  static void runMyIsolate(List<dynamic> args) {
    var sendPort = args[0] as SendPort;
    print("In runMyIsolate ");
    Isolate.exit(sendPort, args);
  }
}

Comments

[Varun Verma]

this the official doc which I have followed. They are saying we can only pass primitive data type but I am getting Error with the similar code.

[Varun Verma]

Even this code also generating the same problem. void onPressed() async { await Isolate.spawn(gotoNext, "OK"); } void gotoNext(String args) { log(args); }

[pskink]

where are you sending Path object?

[Varun Verma]

I am not sending bro. Thats why I am also unable to track the root cause of the problem. I have simply calling the onPressed Function on a TextButton Tap.

[Varun Verma]

>E/flutter (12519): [ERROR:flutter/lib/ui/ui_dart_state.cc(209)] Unhandled Exception: Invalid argument(s): Illegal argument in isolate message: (object extends NativeWrapper - Library:'dart:ui' Class: Path) E/flutter (12519): #0 Isolate._spawnFunction (dart:isolate-patch/isolate_patch.dart:395:25) E/flutter (12519): #1 Isolate.spawn (dart:isolate-patch/isolate_patch.dart:375:7) E/flutter (12519): #2 _Screen1State.onPressed (package:practice/screen_1.dart:32:19) E/flutter (12519): #3 _InkResponseState._handleTap (package:flutter/src/material/ink_well.dart:989:21)

[pskink]

i used that code: void onPressed() async { var receivePort = ReceivePort(); await Isolate.spawn(gotoNext, [receivePort.sendPort]); final msg = await receivePort.first; print('received >$msg<'); } void gotoNext(List<dynamic> args) { SendPort sendPort = args[0]; print('>input parameters: $args<'); Isolate.exit(sendPort, "OK"); } and this is what i see on the logs after calling onPressed function: [+5088 ms] flutter: >input parameters: [SendPort]< [ +12 ms] flutter: received >OK<

[Varun Verma]

Can you please let me know your flutter and dart version. cos I am using latest one.

[pskink]

Flutter 2.11.0-0.1.pre • channel beta • https://github.com/flutter/flutter.git Framework • revision b101bfe32f (3 weeks ago) • 2022-02-16 07:36:54 -0800 Engine • revision e355993572 Tools • Dart 2.17.0 (build 2.17.0-69.2.beta) • DevTools 2.10.0-dev.1

[Varun Verma]

Actually it is not running inside any Widget class. can you guide me how I can achieve this now ?

[Varun Verma]

But List<SendPort> will not be the primitive type? Also I have tried to Pass Map, String and int value but problem was remains.

[Varun Verma]

check this documentation provided here.

[Phạm Anh Tú]

pls try: ``` SendPort sendPort = args[0] as SendPort; ```

[Varun Verma]

This was an Unnecessary cast bro. Also Not working.

[Phạm Anh Tú]

@VarunVerma see my edit

[Phạm Anh Tú]

@VarunVerma add "final result = jsonDecode(fileData) as Map<String, dynamic>;"

[Varun Verma]

Nothing is helping bro.. feeling hopeless now.

[Varun Verma]

Is this example working for you ?

[Phạm Anh Tú]

maybe you used jsonDecode and Isolate.exit wrong way

[Phạm Anh Tú]

i don't know what you want to do, in this case i wouldn't use "result" like that

[Varun Verma]

Exactly you are right! It is working in main thread but not from a Widget class. void main() async { runApp(MyApp()); var receivePort = ReceivePort(); await Isolate.spawn(gotoNext, [receivePort.sendPort]); final msg = await receivePort.first; print('received >$msg<'); } void gotoNext(List<dynamic> args) { SendPort sendPort = args[0]; print('>input parameters: $args<'); Isolate.exit(sendPort, "OK"); }

[Varun Verma]

Yes Now it is working for me Thanks!

[Varun Rajput]

Good to hear that.