如何在flutter的google地图中添加多个标记

import 'package:flutter/material.dart';
import 'package:google_maps_flutter/google_maps_flutter.dart';

class GoogleMapPage extends StatefulWidget {
  @override
  _GoogleMapPageState createState() => _GoogleMapPageState();
}

class _GoogleMapPageState extends State<GoogleMapPage> {
  GoogleMapController _mapController;
  Set<Marker> _markers = {};

  void _onMapCreated(GoogleMapController controller) {
    _mapController = controller;

    setState(() {
      _markers.add(
        Marker(
          markerId: MarkerId('marker1'),
          position: LatLng(37.7749, -122.4194),
          icon: BitmapDescriptor.defaultMarker,
          infoWindow: InfoWindow(
            title: 'Marker 1',
            snippet: 'This is marker 1',
          ),
        ),
      );

      _markers.add(
        Marker(
          markerId: MarkerId('marker2'),
          position: LatLng(37.3382, -121.8863),
          icon: BitmapDescriptor.defaultMarkerWithHue(BitmapDescriptor.hueBlue),
          infoWindow: InfoWindow(
            title: 'Marker 2',
            snippet: 'This is marker 2',
          ),
        ),
      );
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Google Map'),
      ),
      body: GoogleMap(
        onMapCreated: _onMapCreated,
        initialCameraPosition: CameraPosition(
          target: LatLng(37.7749, -122.4194),
          zoom: 12.0,
        ),
        markers: _markers,
      ),
    );
  }
}