GMapsPlusLocation.dart

class GoogleMapsDemo extends StatefulWidget {
  @override
  _GoogleMapsDemoState createState() => _GoogleMapsDemoState();
}

class _GoogleMapsDemoState extends State<GoogleMapsDemo> {
  GoogleMapController mapController;
  Location location = Location();

  Marker marker;

  @override
  void initState() {
    super.initState();
    location.onLocationChanged().listen((location) async {
      if(marker != null) {
        mapController.removeMarker(marker);
      }
      marker = await mapController?.addMarker(MarkerOptions(
        position: LatLng(location["latitude"], location["longitude"]),
      ));
      mapController?.moveCamera(
        CameraUpdate.newCameraPosition(
          CameraPosition(
            target: LatLng(
              location["latitude"],
              location["longitude"],
            ),
            zoom: 20.0,
          ),
        ),
      );
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Column(
        children: <Widget>[
          Container(
            height: MediaQuery.of(context).size.height,
            width: MediaQuery.of(context).size.width,
            child: GoogleMap(
              onMapCreated: (GoogleMapController controller) {
                mapController = controller;
              },
              options: GoogleMapOptions(
                cameraPosition: CameraPosition(
                  target: LatLng(37.4219999, -122.0862462),
                ),
                myLocationEnabled: true,
              ),
            ),
          ),
        ],
      ),
    );
  }
}