在 stream.listen() 完成后 Flutter-Firebase 等待返回

Question

Flutter Stream 问题 我正在尝试通过geohash 过滤我的数据库查询，所以我使用的是 Geoflutterfire，它返回一个 Stream。我尝试将来自Stream<List<>> 中的每个DocumentSnapshot 的数据转换为List。它有效，但问题是return 发生在stream.listen() 的实际完成之前。如何延迟 return 以返回 stream.listen 结果？ 我尝试使用await for(...)，但它出错了。

import 'dart:async';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:flutter_redux/flutter_redux.dart';
import 'package:geoflutterfire/geoflutterfire.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:firebase_storage/firebase_storage.dart';
import 'package:google_maps_flutter/google_maps_flutter.dart';
import 'package:uerto/models/index.dart';

class SearchApi {
  const SearchApi({required FirebaseAuth auth, required FirebaseFirestore firestore, required FirebaseStorage storage, required Geoflutterfire geo})
      : _auth = auth,
        _firestore = firestore,
        _storage = storage,
        _geo = geo;

  final FirebaseAuth _auth;
  final FirebaseFirestore _firestore;
  final FirebaseStorage _storage;
  final Geoflutterfire _geo;

  Future<List<AppClient>> getClientList(LatLng location, String category, String subCategory, double radius, int limit) async{

    final List<AppClient> newResult = <AppClient>[];
    final GeoFirePoint center = _geo.point(latitude: location.latitude, longitude: location.longitude);
    final Query<Map<String, dynamic>> collectionReference = _firestore.collection('London$category/$subCategory/UID').limit(limit);
    const String field = 'position';
    final Stream<List<DocumentSnapshot<Map<String, dynamic>>>> stream = _geo.collection(collectionRef: collectionReference).within(center: center, radius: radius, field: field);
    // ignore: always_specify_types
    stream.listen((List<DocumentSnapshot> documentList) {
      // ignore: always_specify_types, avoid_function_literals_in_foreach_calls
      documentList.forEach((DocumentSnapshot document) async {
        ///print(document.data());
        final SearchUid searchUid = SearchUid.fromJson(document.data());
        //print(searchUid.uid);
        final DocumentSnapshot<Map<String, dynamic>> client = await _firestore.collection('clients').doc(searchUid.uid).get();
        final AppClient clientData = AppClient.fromJson(client.data());
        print(clientData);
        newResult.add(clientData);
      });
    });
    await for(List<DocumentSnapshot> documentList in stream){
      return newResult;
    }

  }
}

Answer 1

因此，您可以尝试在流后使用 .onDone。因此，如果流结束，onDone 块将运行。

 stream.listen((List<DocumentSnapshot> documentList) {

}).onDone((){
 //run here
});

Answer 2

您无需侦听即可仅从流中获取首次数据。

初始化流后，执行以下操作：

List<DocumentSnapshot> documentList = await stream.first;
// Do your operations here
return newResult;

Answer 3

@ChetanGoyal 如您所见，这不是错误。它跳过第 33-41 行（这是异步的和等待的）的事实很奇怪......你可以看到返回的打印是空的，并且在第 39 行的打印之前发生。