如何在initState()中正确初始化Stream

Question

我正在尝试使用这个示例来实现flutter包“计步器”。

我在加载的第一个页面中从 initState() 调用提供程序方法。 问题是计步器监听器/流在初始应用程序安装时不起作用，重新启动后所有接缝都按预期工作。

  @override
  void initState() {
    WidgetsBinding.instance.addPostFrameCallback((timeStamp) {
      final myProvider = Provider.of<MyProvider>(context, listen: false);
      myProvider.initPlatformState();
    });

我的提供者类别：

class MyProvider extends ChangeNotifier {
 ...
  late Stream<StepCount> _stepCountStream;
  late Stream<PedestrianStatus> _pedestrianStatusStream;

  void initPlatformState() {
    Stream<PedestrianStatus>  _pedestrianStatusStream = Pedometer.pedestrianStatusStream;
    pedestrianStatusStream
        .listen(onPedestrianStatusChanged)
        .onError(onPedestrianStatusError);

    Stream<StepCount>   _stepCountStream = Pedometer.stepCountStream;
    stepCountStream.listen(onStepCount).onError(onStepCountError);

  }
}

I tried to move Stream variables into initPlatformState() but same result.
I added permissions and all...
Working only if i hot restart or go to other page and reload  Provider.of<MyProvider>(context, listen: false).initPlatformState();

Answer 1

试试这个：

class MyProvider extends ChangeNotifier {
 ...
  late Stream<StepCount> _stepCountStream;
  late Stream<PedestrianStatus> _pedestrianStatusStream;

  void initPlatformState() {
    Stream<PedestrianStatus>  _pedestrianStatusStream = Pedometer.pedestrianStatusStream;
    pedestrianStatusStream
        .listen(onPedestrianStatusChanged)
        .onError(onPedestrianStatusError);

    Stream<StepCount>   _stepCountStream = Pedometer.stepCountStream;
    stepCountStream.listen(onStepCount).onError(onStepCountError);

notifyListeners();
  }
}