如何在flutter中按日期将firestore中的数据排序到地图

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

class MapScreen extends StatefulWidget {
  @override
  _MapScreenState createState() => _MapScreenState();
}

class _MapScreenState extends State<MapScreen> {
  GoogleMapController mapController;
  List<Marker> markers = [];

  @override
  void initState() {
    super.initState();
    getSortedData();
  }

  void getSortedData() async {
    QuerySnapshot snapshot = await FirebaseFirestore.instance
        .collection('maps')
        .orderBy('date', descending: true)
        .get();

    setState(() {
      markers = snapshot.docs.map((doc) {
        // 根据文档数据创建标记
        return Marker(
          markerId: MarkerId(doc.id),
          position: LatLng(doc['latitude'], doc['longitude']),
          infoWindow: InfoWindow(title: doc['title']),
        );
      }).toList();
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Map'),
      ),
      body: GoogleMap(
        onMapCreated: (controller) {
          setState(() {
            mapController = controller;
          });
        },
        initialCameraPosition: CameraPosition(
          target: LatLng(0, 0),
          zoom: 2,
        ),
        markers: Set<Marker>.of(markers),
      ),
    );
  }
}