Полилиния Google Maps не отображается

Я пытаюсь, чтобы в виджете GoogleMaps моего приложения Flutter Dart для Android появилось несколько полилиний, но они не отображаются. Виджет и карта отображаются отлично, но полилинии отсутствуют.

Когда мой код запускается, ломаная линия успешно добавляется в _polylines, а виджет GoogleMaps содержит «polylines: _polylines», они по-прежнему не отображаются.

есть идеи?

Мой код выглядит следующим образом:

class TotalStatsViewModel extends BaseViewModel {
  final _navigationService = locator<NavigationService>();
  Set<Polyline> _polylines = HashSet<Polyline>();
  GoogleMapController mapController;

  Widget getWidget() {
    if (getLoggedInUser().activityList.length != 0) {
      return Column(
        children: [
          getMap(),
          Text(
            'Total Distance Biked:',
            textScaleFactor: 2,
          ),
          Text(
            getTotalDistance(),
            textScaleFactor: 1.5,
          ),
          Text(
            'Total Duration Biked:',
            textScaleFactor: 2,
          ),
          Text(
            getTotalDuration(),
            textScaleFactor: 1.5,
          ),
          Text(
            'Average Biking Speed:',
            textScaleFactor: 2,
          ),
          Text(
            getAverageSpeed(),
            textScaleFactor: 1.5,
          ),
          Spacer(),
          Padding(
              padding: const EdgeInsets.all(10.0),
              child: ElevatedButton(
                onPressed: () {
                  routeToHubView();
                },
                child: Text('Return'),
              )),
          Row(), //Row is here to center the column by adding a max width element.
        ],
      );
    } else {
      return Column(
        children: [
          Text(
            'User needs at least one added activity to display statistics.',
            textScaleFactor: 1.5,
            textAlign: TextAlign.center,
          ),
          Spacer(),
          Padding(
              padding: const EdgeInsets.all(10.0),
              child: ElevatedButton(
                onPressed: () {
                  routeToHubView();
                },
                child: Text('Return'),
              )),
          Row(), //Row is here to center the column by adding a max width element.
        ],
      );
    }
  }

  Widget getMap() {
    for (int i = 0; i < getLoggedInUser().activityList.length; i++) {
      constructPolyline(getLoggedInUser().activityList[i]);
    }
    return SizedBox(
      height: 300,
      child: GoogleMap(
        mapType: MapType.normal,
        onMapCreated: _onMapCreated,
        initialCameraPosition: CameraPosition(
          //target: LatLng(45.521563, -122.677433),
          target: LatLng(47.6645740, -122.0411640),
          zoom: 11.0,
        ),
        polylines: _polylines,
      ),
    );
  }

  void constructPolyline(Activity activity) {
    print('CONSTRUCT POLYLINE CALLED');
    List<LatLng> polylineLatLongs = [];
    //fix with activity
    Gpx gpx = GpxReader().fromString('<?xml version = "1.0" encoding = "UTF-8"?>'
        '<gpx creator = "StravaGPX" xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation = "http://www.topografix.com/GPX/1/1 http://www.topografix.com/GPX/1/1/gpx.xsd http://www.garmin.com/xmlschemas/GpxExtensions/v3 http://www.garmin.com/xmlschemas/GpxExtensionsv3.xsd http://www.garmin.com/xmlschemas/TrackPointExtension/v1 http://www.garmin.com/xmlschemas/TrackPointExtensionv1.xsd" version = "1.1" xmlns = "http://www.topografix.com/GPX/1/1" xmlns:gpxtpx = "http://www.garmin.com/xmlschemas/TrackPointExtension/v1" xmlns:gpxx = "http://www.garmin.com/xmlschemas/GpxExtensions/v3">'
        '<metadata>'
        '<time>2022-02-06T21:22:54Z</time>'
        '</metadata>'
        '<trk>'
        '<name>Afternoon Ride</name>'
        '<type>1</type>'
        '<trkseg>'
        '<trkpt lat = "47.6645740" lon = "-122.0411640">'
        '<ele>113.0</ele>'
        '<time>2022-02-06T21:22:54Z</time>'
        '<extensions>'
        '<power>0</power>'
        '<gpxtpx:TrackPointExtension>'
        '<gpxtpx:atemp>22</gpxtpx:atemp>'
        '<gpxtpx:hr>85</gpxtpx:hr>'
        '<gpxtpx:cad>37</gpxtpx:cad>'
        '</gpxtpx:TrackPointExtension>'
        '</extensions>'
        '</trkpt>'
        '<trkpt lat = "47.6645750" lon = "-122.0411670">'
        '<ele>128.0</ele>'
        '<time>2022-02-06T21:22:55Z</time>'
        '<extensions>'
        '<power>0</power>'
        '<gpxtpx:TrackPointExtension>'
        '<gpxtpx:atemp>22</gpxtpx:atemp>'
        '<gpxtpx:hr>87</gpxtpx:hr>'
        '<gpxtpx:cad>37</gpxtpx:cad>'
        '</gpxtpx:TrackPointExtension>'
        '</extensions>'
        '</trkpt>');
    //debug code
    print('trks: ' + gpx.trks.length.toString());
    print('trksegs: ' + gpx.trks[0].trksegs.length.toString());
    print('trkpts: ' + gpx.trks[0].trksegs[0].trkpts.length.toString());

    for (int i = 0; i < gpx.trks.length; i++) {
      for (int j = 0; j < gpx.trks[i].trksegs.length; j++) {
        for (int k = 0; k < gpx.trks[i].trksegs[j].trkpts.length; k++) {
          polylineLatLongs.add(LatLng(gpx.trks[i].trksegs[j].trkpts[k].lat,
              gpx.trks[i].trksegs[j].trkpts[k].lon));
          print('ITERATION DONE');
        }
      }
    }
    print(polylineLatLongs.toString());
    //polylineLatLongs.add(LatLng(47.664574, -122.041164));
    //polylineLatLongs.add(LatLng(47.664575, -122.041167));

    _polylines.add(Polyline(
        polylineId: PolylineId('0'),
        points: polylineLatLongs,
        color: Colors.red,
        visible: true,
        width: 10));
    print(_polylines.toString());
  }

  void _onMapCreated(GoogleMapController controller) {
    mapController = controller;
  }

  String getTotalDistance() {
    User user = getLoggedInUser();
    double distanceSum = 0;
    for (int i = 0; i < user.activityList.length; i++) {
      distanceSum += user.activityList[i].distance;
    }
    distanceSum = double.parse((distanceSum).toStringAsFixed(2));
    return distanceSum.toString() + ' miles';
  }

  String getTotalDuration() {
    User user = getLoggedInUser();
    int totalSeconds = 0;
    for (int i = 0; i < user.activityList.length; i++) {
      totalSeconds += user.activityList[i].duration.inSeconds;
    }
    Duration totalDuration = Duration(seconds: totalSeconds);
    List<String> splitDistance = totalDuration.toString().split('.');
    return splitDistance[0];
  }

  String getAverageSpeed() {
    User user = getLoggedInUser();
    double avgSpeed = 0;
    for (int i = 0; i < user.activityList.length; i++) {
      avgSpeed += user.activityList[i].avgerageSpeed;
    }
    avgSpeed /= user.activityList.length;
    avgSpeed = double.parse((avgSpeed).toStringAsFixed(2));
    return avgSpeed.toString() + ' miles per hour';
  }

  void routeToHubView() {
    _navigationService.navigateTo(HubViewRoute);
  }
}