Flutter-Firestore 将 Stream<List<DocumentSnapshot<Map<String, dynamic>>>> 转换为 List<MyClass>

Question

我创建了一个函数，我想 return 数据库中半径内的所有位置。这就是我使用 GeoFlutterFire 的原因。我的问题是我不知道如何将 Stream>>> 转换为 List<>我的 Class 类型。


import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:geoflutterfire/geoflutterfire.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:firebase_storage/firebase_storage.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() async{

    final List<AppClient> newResult = <AppClient>[];

    final GeoFirePoint center = _geo.point(latitude: 44.414445, longitude: 26.01135501);

    final CollectionReference<Map<String, dynamic>> collectionReference = _firestore.collection('clients/London/Beauty');

    final double radius = 5000;
    const String field = 'point';

    final  Stream<List<DocumentSnapshot<Map<String, dynamic>>>> stream = _geo.collection(collectionRef: collectionReference).within(center: center, radius: radius, field: field);

    ///something to transform Stream<List<DocumentSnapshot<Map<String, dynamic>>>> stream into List<AppClient> result;

    newResult.addAll(result);

    return newResult;

  }
}

Answer 1

stream.listen((List<DocumentSnapshot> documentList) {
  // this function would be called when ever documentList changes.
  // So, it might be called even after your getClientsList() is completed.
  List<Map<String, dynamic>> newResult = documentList.map((e) => e.data()).toList();
});

由于 getClientsList returns 未来，您可能希望将流转换为未来。在这种情况下，您可以使用它。

List<Map<String, dynamic>> newResult = (await stream.first).map((e) => e.data()).toList();

或者，您可以使用流生成器收听流。像这样。

StreamBuilder<DocumentSnapshot>(
  stream: _geo.collection(collectionRef: collectionReference)
      .within(center: center, radius: radius, field: field),
  builder:
      (BuildContext context, AsyncSnapshot<DocumentSnapshot> snapshot) {
    if (snapshot.hasError) return Text('Something went wrong');
    if (snapshot.connectionState == ConnectionState.waiting)
      return CircularProgressIndicator();

    List<Map<String, dynamic>> newResult = snapshot.data.data();
    print(newResult);
    return SizedBox();
  },
)

Answer 2

Streams 非常有用，它提供了许多开箱即用的优雅解决方案。

在你的情况下，我会使用 StreamTransformer 来做这样的事情：

Stream<CustomType> stream = _geo.collection(collectionRef: collectionReference)
   .within(center: center, radius: radius, field: field)
   .transform(StreamTransformer.fromHandlers(handleData: (docSnap, sink) {
      if (docSnap.exists) {
         sink.add(<convert docSnap fields to CustomType here>);
      }
}));

您可以使用 Streams 和 StreamTransformer 做更多事情，让您的代码更易于阅读和调试，而且更漂亮。关于 StreamTransformer 的文档： https://api.flutter.dev/flutter/dart-async/StreamTransformer-class.html

编辑：免责声明，此答案基于 Stream 文件类而不是 geo flutter fire - 我对此没有经验。

Flutter-Firestore 将 Stream<List<DocumentSnapshot<Map<String, dynamic>>>> 转换为 List<MyClass>

Flutter-Firestore transform Stream<List<DocumentSnapshot<Map<String, dynamic>>>> into List<MyClass>

firebase

flutter

dart

google-cloud-firestore

geohashing