flutter - 如何将Future 转换为Stream

Question

在我的Flutter应用中，我有一个返回Future的函数，但我想将结果作为Stream。这是函数:

  Future<bool> isGpsOn() async {
    if (await Geolocator().isLocationServiceEnabled()) {
      return true;
    } else {
      return false;
    }
  }

怎么做？

Answer 1

阅读manual并检查我的答案:

Stream<bool> gpsStatusStream() async* {
  bool enabled;
  while (true) {
    try {
      bool isEnabled = await Geolocator().isLocationServiceEnabled();
      if (enabled != isEnabled) {
        enabled = isEnabled;
        yield enabled;
      }
    }
    catch (error) {}
    await Future.delayed(Duration(seconds: 5));
  }
}

gpsStatusStream().listen((enabled) {
  print(enabled ? 'enabled' : 'disabled');
});

或创建转换器:

Stream futureToStream(fn, defaultValue, Duration duration) async* {
  var result;
  while (true) {
    try {
      result = await fn();
    }
    catch (error) {
      result = defaultValue;
    }
    finally {
      yield result;
    }
    await Future.delayed(duration);
  }
}

Future<bool> isGpsOn() async {
  return await Geolocator().isLocationServiceEnabled();
}

final gpsStatusStream = futureToStream(isGpsOn, false, Duration(seconds: 5));
gpsStatusStream.listen((enabled) {
  print(enabled ? 'enabled' : 'disabled');
});