即使关闭应用程序，如何在后台运行任务并获取任务生成的最新结果并在打开应用程序时显示？

Question

我想在flutter中创建一个计步器应用程序，因此我使用了Flutter计步器插件，并且效果很好，但是即使主应用程序已关闭，我也想每次都运行此插件来计算用户步数。

我发现我可以使用dart隔离器创建一个任务，该任务可以在远离主线程的另一个线程中运行，并通过端口在它们之间进行通信。

  String _stepCountValue = '0';
  ReceivePort _receivePort;
  Isolate isolate;

  iniState() {
    super.initState();
    _start();
  }

  void _start() async {
    _receivePort = ReceivePort();
    isolate = await Isolate.spawn(initPlatformState, 
    _receivePort.sendPort);
    _receivePort.listen((data) {
      print(data);
      setState(() {
        _stepCountValue = "$data";
      });
    }, onDone: () {
      print("done!");
    });
  }

  static void initPlatformState(SendPort sendPort) async {
    Pedometer pedometer = new Pedometer();
   pedometer.stepCountStream.listen((int stepCountValue) {
      print("------------------> $stepCountValue");
      sendPort.send(stepCountValue);
    }, onError: (error){print(error);}, onDone: (){}, cancelOnError: 
   true);
  }

我希望输出为用户步骤数。

但是我得到了这个错误

I/flutter (26151): ══╡ EXCEPTION CAUGHT BY SERVICES LIBRARY ╞══════════════════════════════════════════════════════════
I/flutter (26151): The following _CompileTimeError was thrown while activating platform stream on channel
I/flutter (26151): pedometer.eventChannel:
I/flutter (26151): error: native function 'Window_sendPlatformMessage' (4 arguments) cannot be found
I/flutter (26151): When the exception was thrown, this was the stack:
I/flutter (26151): #0      Window.sendPlatformMessage (dart:ui/window.dart:868:9)
I/flutter (26151): #1      BinaryMessages._sendPlatformMessage (package:flutter/src/services/platform_messages.dart:46:15)
I/flutter (26151): #2      BinaryMessages.send (package:flutter/src/services/platform_messages.dart:97:12)
I/flutter (26151): #3      MethodChannel.invokeMethod (package:flutter/src/services/platform_channel.dart:295:50)
I/flutter (26151): <asynchronous suspension>
I/flutter (26151): #4      EventChannel.receiveBroadcastStream.<anonymous closure> (package:flutter/src/services/platform_channel.dart:490:29)
I/flutter (26151): <asynchronous suspension>
I/flutter (26151): #12     StepCounterState.initPlatformState (package:stepcounter/main.dart:59:30)
I/flutter (26151): <asynchronous suspension>
I/flutter (26151): #13     _startIsolate.<anonymous closure> (dart:isolate-patch/isolate_patch.dart:303:17)
I/flutter (26151): #14     _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:171:12)
I/flutter (26151): (elided 7 frames from package dart:async)