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我想在 Flutter 中创建一个计步器应用程序，所以我使用了 Flutter 计步器插件，它运行良好，但我想每次都运行这个插件来计算用户步数，即使主应用程序已关闭。

我发现我可以使用 dart 隔离来创建一个任务，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);
  }

我希望输出是用户步骤数。

但我得到那个错误

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)
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