I want to have a dart background service running forever (isolates) which will communicate with a server through websockets. And I have an API for Android which gather information to send to the server. How can I invoke that Android methods which use callbacks and everything from the background isolate?

EDIT

So far in dart I created an Isolate to periodically invoke the poolSong method in background even if the user is using another app or has the screen turned off.

But that gives me the error below...on the github issues they say that I can't send a platform message from a different Isolate unless it's the main. But if I do it from the main isolate, when the user exit the app that isolate will terminate too.

MainDart

class _MyHomePageState extends State<MyHomePage> {
    final GlobalKey<ScaffoldState> scaffoldKey = new GlobalKey<ScaffoldState>();
    static const platform = const MethodChannel('mainService');

    static _poolSong(SendPort sendPort) async {
        const oneSec = const Duration(seconds:1);
        new Timer.periodic(oneSec, (Timer t) => platform.invokeMethod('poolSong'));
    }

    @override
    void initState() {
        super.initState();
        ReceivePort receivePort = ReceivePort();
        Isolate.spawn(_poolSong, receivePort.sendPort);
    }
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MainActivityJava

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    GeneratedPluginRegistrant.registerWith(this);

    new MethodChannel(getFlutterView(), CHANNEL).setMethodCallHandler(
        (call, result) -> {
            if (call.method.equals("startService"))
                startService();
            if (call.method.equals("poolSong"))
                poolSong();
        }
    );
}

ERROR

E/flutter (25412): [ERROR:flutter/runtime/dart_isolate.cc(717)] Isolate (765499726) 'main.dart:_poolSong()' exited with an error
E/flutter (25412): [ERROR:flutter/shell/common/shell.cc(186)] Dart Error: Unhandled exception:
E/flutter (25412): error: native function 'Window_sendPlatformMessage' (4 arguments) cannot be found
E/flutter (25412): #0   Window.sendPlatformMessage (dart:ui/window.dart:811:9)
E/flutter (25412): #1   BinaryMessages._sendPlatformMessage (package:flutter/src/services/platform_messages.dart:39:15)
E/flutter (25412): #2   BinaryMessages.send (package:flutter/src/services/platform_messages.dart:87:12)
E/flutter (25412): #3   MethodChannel.invokeMethod (package:flutter/src/services/platform_channel.dart:286:49)
E/flutter (25412): <asynchronous suspension>
E/flutter (25412): #4   _MyHomePageState._poolSong.<anonymous closure> (package:musictie/main.dart:37:54)
E/flutter (25412): #5   _Timer._runTimers (dart:isolate/runtime/libtimer_impl.dart:382:19)
E/flutter (25412): #6   _Timer._handleMessage (dart:isolate/runtime/libtimer_impl.dart:416:5)
E/flutter (25412): #7   _RawReceivePortImpl._handleMessage (dart:isolate/runtime/libisolate_patch.dart:171:12)


Solution 1: AnasSafi

This error happens when trying to run dart code when the app is in the garbage (app closed), Until now the best way for dealing with background service is to do what you need in native code, and dont try to run anything from dart when app closed.