在地图上显示 firebase 子集合的引脚 - Flutter

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【中文标题】在地图上显示 firebase 子集合的引脚 - Flutter【英文标题】:Show pins of a subcollection of firebase on map - Flutter 【发布时间】:2020-12-23 02:38:25 【问题描述】:

我有一个应用程序可以从 firebase 读取停车数据并在地图上显示一些图钉。现在应用程序只显示停车场的图钉,但我还想在地图上添加保存在 Parkings 集合的“lots”子集合中的每个停车场的图钉。我该怎么做?

maps.dart:

class StoreMap extends StatelessWidget 
  StoreMap(
    Key key,
    @required this.documents,
    @required this.initialPosition,
  ) : super(key: key);

  
  final List<DocumentSnapshot> documents;
  final LatLng initialPosition;
  final Completer<GoogleMapController> _controller = Completer();

  static final CameraPosition _initialPosition = CameraPosition(
    target: LatLng(45.791789, 24.150390),
    zoom: 16,
  );


  @override
  Widget build(BuildContext context) 
    return Scaffold(
      body: GoogleMap(
        mapType: MapType.hybrid,
        initialCameraPosition: _initialPosition,
        onMapCreated: (GoogleMapController controller) 
          _controller.complete(controller);
        ,
        myLocationEnabled: true,
        markers:documents.map((document) => new Marker(
                  markerId: MarkerId(document.get('name')),
                  position: LatLng(
                    document.get('location').latitude,
                    document.get('location').longitude,
                  ),
                  onTap: () => _changeMap(LatLng(
                    document.get('location').latitude,
                    document.get('location').longitude,
                  )),
                  infoWindow: InfoWindow(
                      title: document.get('name'),
                      snippet: document.get('numberOfLots')),
             icon: BitmapDescriptor.defaultMarkerWithHue(BitmapDescriptor.hueViolet)),
                )
            .toSet()
      ),
  floatingActionButton: FloatingActionButton(
        onPressed: _currentLocation,
        child: Icon(Icons.location_searching),
        backgroundColor: Colors.deepPurple[400],
      ),
    );
  

【问题讨论】:

document.collection("lots").get('location').latitude 不起作用,因为您在 collection("lots") 之后没有指定任何文档 写 document.collection("lots").document("h6nU1Gyx4Tlb5rpGYi5e").get('location').latitude 也不起作用 【参考方案1】:

document.collection("lots").document("DocumentId").get('location').latitude 不起作用的原因是您不应该将字段名称传递给 get 方法。同样在您的代码中,document 只是一个文档快照,因此您要做的是获取该文档的 id,然后访问其子集合和子文档。

你可以这样做:

//The code below gets the document ids of the parking collection
//gets access the sub collection "lots" and gets all the documents inside it.
//and for every sub document, gets the data and prints the latitude of the location field
for (DocumentSnapshot document in documents)
    String documentId = document.documentId;
    DocumentReference parkingDocReference = 
    Firestore.instance.collection("Parkings").document(documentId);
    parkingDocReference.collection("lots")
    .get((QuerySnapshot subDocuments)
    List<DocumentSnapshot> subDocumentsSnapshots = subDocuments.documents;
    for (DocumentSnapshot subDoc in subDocumentsSnapshots)
         String subDocId = subDoc.documentId;
         parkingDocReference.collection("lots")
         .document(subDocId).get().then((DocumentSnapshot snapshot) 
             print(snapshot.data["location"].latitude); //prints the latitude;
         
  
     
  );


get() 将返回 Future&lt;DocumentSnapshot&gt;,这就是为什么我们在 get() 之后使用 .then() 以便该函数仅在检索数据时运行

更新: 为了查看地图上的标记,我们将上面的代码放在返回Future&lt;List&lt;Marker&gt;&gt; 的函数中。返回结果后,您可以调用 setState 并在您的小部件树中使用更新后的列表。

最好使用async/await 而不是then,因为它会强制程序首先从未来获取结果。

Future<List<Marker>> _createMarkersForLotsAndParkings() async
   List<Marker> markersList = [];
   int markerId = 0;
   for (DocumentSnapshot document in widget.documents)
    // ignore: deprecated_member_use
    String documentId = document.documentID;
    DocumentReference parkingDocReference = 
    // ignore: deprecated_member_use
    Firestore.instance.collection("Parkings").document(documentId);
    DocumentSnapshot parkingDocRef = await parkingDocReference.get();
    markersList.add(Marker(
                  markerId: MarkerId(markerId.toString()),
                  position: LatLng(parkingDocRef.get('location').latitude,
                      parkingDocRef.get('location').longitude),
                  onTap: () => _changeMap(LatLng(
                      parkingDocRef.get('location').latitude,
                      parkingDocRef.get('location').longitude)),
                  infoWindow: InfoWindow(
                      title: document.get('name'),
                      snippet: document.get('numberOfLots')),
                  icon: BitmapDescriptor.defaultMarkerWithHue(BitmapDescriptor.hueYellow)),
            );
            markerId++;
    QuerySnapshot subDocuments = await parkingDocReference.collection("lots").get();
    // ignore: deprecated_member_use
    // ignore: deprecated_member_use
    List<DocumentSnapshot> subDocumentsSnapshots = subDocuments.documents;
    for (DocumentSnapshot subDoc in subDocumentsSnapshots)
         // ignore: deprecated_member_use
         String subDocId = subDoc.documentID;
         DocumentSnapshot snapshot = await parkingDocReference.collection("lots")
         // ignore: deprecated_member_use
         .document(subDocId).get();
            print(snapshot.get('location').latitude);

            markersList.add(
              Marker(
                  markerId:MarkerId(markerId.toString()),
                  position: LatLng(snapshot.get('location').latitude,
                      snapshot.get('location').longitude),
                  onTap: () => _changeMap(LatLng(
                      snapshot.get('location').latitude,
                      snapshot.get('location').longitude)),
                  infoWindow: InfoWindow(
                      title: document.get('name'),
                      snippet: document.get('numberOfLots')),
                  icon: BitmapDescriptor.defaultMarkerWithHue(BitmapDescriptor.hueViolet)),
            );
            markerId++;

     


return Future.value(markersList);




我们在initState() 中调用这个函数。您需要将StoreMap 转换为StatefullWidget 才能调用setState 并使用initState


@override
  void initState() 
    super.initState();
    _createMarkersForLots().then((List<Marker> lotsMarkers)
    setState(()
    markers = lotsMarkers; //rebuilds the screen with the lotsMarkers. make sure to use the markers in your widget tree to see the markers
  );
    
);

您的完整代码必须如下所示:

import 'dart:async';

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

class StoreMap extends StatefulWidget 
  StoreMap(
    Key key,
    @required this.documents,
    @required this.initialPosition,
  ) : super(key: key);

  final List<DocumentSnapshot> documents;
  final LatLng initialPosition;
  static final CameraPosition _initialPosition = CameraPosition(
    target: LatLng(45.791789, 24.150390),
    zoom: 16,
  );


  @override
  _StoreMapState createState() => _StoreMapState();


class _StoreMapState extends State<StoreMap> 
  final Completer<GoogleMapController> _controller = Completer();


List<Marker> markers = [];
Future<List<Marker>> _createMarkersForLotsAndParkings() async
   List<Marker> markersList = [];
   int markerId = 0;
   for (DocumentSnapshot document in widget.documents)
    // ignore: deprecated_member_use
    String documentId = document.documentID;
    DocumentReference parkingDocReference = 
    // ignore: deprecated_member_use
    Firestore.instance.collection("Parkings").document(documentId);
    DocumentSnapshot parkingDocRef = await parkingDocReference.get();
    markersList.add(Marker(
                  markerId: MarkerId(markerId.toString()),
                  position: LatLng(parkingDocRef.get('location').latitude,
                      parkingDocRef.get('location').longitude),
                  onTap: () => _changeMap(LatLng(
                      parkingDocRef.get('location').latitude,
                      parkingDocRef.get('location').longitude)),
                  infoWindow: InfoWindow(
                      title: document.get('name'),
                      snippet: document.get('numberOfLots')),
                  icon: BitmapDescriptor.defaultMarkerWithHue(BitmapDescriptor.hueYellow)),
            );
            markerId++;
    QuerySnapshot subDocuments = await parkingDocReference.collection("lots").get();
    // ignore: deprecated_member_use
    // ignore: deprecated_member_use
    List<DocumentSnapshot> subDocumentsSnapshots = subDocuments.documents;
    for (DocumentSnapshot subDoc in subDocumentsSnapshots)
         // ignore: deprecated_member_use
         String subDocId = subDoc.documentID;
         DocumentSnapshot snapshot = await parkingDocReference.collection("lots")
         // ignore: deprecated_member_use
         .document(subDocId).get();
            print(snapshot.get('location').latitude);

            markersList.add(
              Marker(
                  markerId:MarkerId(markerId.toString()),
                  position: LatLng(snapshot.get('location').latitude,
                      snapshot.get('location').longitude),
                  onTap: () => _changeMap(LatLng(
                      snapshot.get('location').latitude,
                      snapshot.get('location').longitude)),
                  infoWindow: InfoWindow(
                      title: document.get('name'),
                      snippet: document.get('numberOfLots')),
                  icon: BitmapDescriptor.defaultMarkerWithHue(BitmapDescriptor.hueViolet)),
            );
            markerId++;
  
     


return Future.value(markersList);



@override
  void initState() 
    super.initState();
    _createMarkersForLotsAndParkings().then((List<Marker> lotsMarkers)
    setState(()
    markers = lotsMarkers; 
  );
    
);



  
  @override
  Widget build(BuildContext context) 
    return Scaffold(
      body: GoogleMap(
        zoomGesturesEnabled: true,
        mapType: MapType.hybrid,
        initialCameraPosition: StoreMap._initialPosition,
        onMapCreated: (GoogleMapController controller) 
          _controller.complete(controller);
        ,
        myLocationEnabled: true,
        markers: markers.toSet(),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _currentLocation,
        child: Icon(Icons.location_searching),
        backgroundColor: Colors.deepPurple[400],
      ),
    );
  

  void _currentLocation() async 
    final GoogleMapController controller = await _controller.future;
    LocationData currentLocation;
    var location = new Location();
    try 
      currentLocation = await location.getLocation();
     on Exception 
      currentLocation = null;
    

    controller.animateCamera(CameraUpdate.newCameraPosition(
      CameraPosition(
        bearing: 0,
        target: LatLng(currentLocation.latitude, currentLocation.longitude),
        zoom: 18.0,
      ),
    ));
  

  _changeMap(LatLng position) async 
    final GoogleMapController controller = await _controller.future;

    controller.animateCamera(CameraUpdate.newCameraPosition(
      CameraPosition(
        bearing: 0,
        target: LatLng(position.latitude, position.longitude),
        zoom: 19.4,
      ),
    ));
  



Google 地图为具有相同 ID 的标记显示一个标记,因此我们使用 markerId 为每个标记提供唯一 ID 并查看所有标记。

【讨论】:

我收到此错误:方法 'collection' 没有为类型 'DocumentSnapshot' 定义。\n尝试将名称更正为现有方法的名称,或定义一个名为 'collection' 的方法'。” 看看我更新的解决方案并检查它是否有效 我将它添加到一个函数中。我可以在控制台上看到纬度,但我不知道如何将其连接到标记中的 LatLong(...) 以便在 UI 上显示它们。 您可以使用此代码获取坐标。您也可以使用相同的代码创建一个函数,但它必须返回一个标记列表,因此您需要在函数中创建标记。然后使用该列表并在小部件树中创建标记。当你有标记列表时,你可以在 initState 中调用函数并调用 setState 我试过了(请看我添加的最后一条鳕鱼),但标记不会出现。

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