Google Maps Flutter:如何从firebase RTDB放置多个标记

dependencies:
  flutter:
    sdk: flutter
  google_maps_flutter: ^1.2.0

dependencies:
  firebase_core: ^1.0.0
  firebase_database: ^7.0.0

import 'package:firebase_core/firebase_core.dart';

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  runApp(MyApp());
}

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

class MapPage extends StatefulWidget {
  @override
  _MapPageState createState() => _MapPageState();
}

class _MapPageState extends State<MapPage> {
  GoogleMapController mapController;
  DatabaseReference databaseReference;

  @override
  void initState() {
    super.initState();
    databaseReference = FirebaseDatabase.instance.reference().child('markers');
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Google Maps Flutter'),
      ),
      body: GoogleMap(
        onMapCreated: (controller) {
          mapController = controller;
        },
        initialCameraPosition: CameraPosition(
          target: LatLng(37.4219999, -122.0840575), // 设置初始地图位置
          zoom: 12.0, // 设置初始缩放级别
        ),
        markers: Set<Marker>.from([
          Marker(
            markerId: MarkerId('marker1'),
            position: LatLng(37.4219999, -122.0840575),
            infoWindow: InfoWindow(
              title: 'Marker 1',
              snippet: 'This is marker 1',
            ),
          ),
          Marker(
            markerId: MarkerId('marker2'),
            position: LatLng(37.42796133580664, -122.085749655962),
            infoWindow: InfoWindow(
              title: 'Marker 2',
              snippet: 'This is marker 2',
            ),
          ),
        ]),
      ),
    );
  }
}

databaseReference.onChildAdded.listen((event) {
  var markerData = event.snapshot.value;
  var markerId = MarkerId(markerData['id']);
  var marker = Marker(
    markerId: markerId,
    position: LatLng(markerData['latitude'], markerData['longitude']),
    infoWindow: InfoWindow(
      title: markerData['title'],
      snippet: markerData['snippet'],
    ),
  );
  setState(() {
    mapController.addMarker(marker);
  });
});