流不回傳任何值

我有一個顯然不回傳值的流。我在 Streambuilder 中使用的快照沒有回傳任何內容，而是回傳黃色容器（參見下面的代碼），當我的快照沒有資料時回傳該容器。知道是什么導致了這個問題嗎？

下面是所有函式，流以及我的 Streambuilder。

這是更新的流。不列印 otherUserId 列印陳述句。也許錯誤在這里的某個地方。

Stream<List>? roomsListStream() async* {
try {
  print("userId: $userId");
  var rooms = FirebaseFirestore.instance
      .collection("rooms")
      .where("users", arrayContains: userId)
      .orderBy("latestMessageTime", descending: true)
      .snapshots();
  rooms.map((QuerySnapshot query) {
    List<RoomsListModel> retVal = [];
    for (var element in query.docs) {
      // get other user id
      String otherUserId = element["users"][0] == userId
          ? element["users"][1]
          : element["users"][0];
      print("otherUserId: $otherUserId");
      // get other user details
      getOtherUser(otherUserId).then((value) {
        retVal.add(RoomsListModel(
            roomId: element.id,
            otherUserId: otherUserId,
            avatar: value["photoUrl"],
            name: value["name"],
            lastMessage: element["latestMessage"],
            lastMessageTime: element["latestMessageTime"]));
      });
    }
    print(retVal);
    return retVal;
  });
} catch (e) {
  print("Error: $e");
}

}

  import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:flutter/material.dart';
import 'package:blabber_tech/services/auth.dart';
import 'package:blabber_tech/services/chat_services.dart';
import 'package:rxdart/rxdart.dart';
import 'package:blabber_tech/models/room_model.dart';

// Rooms List Model
class RoomsListModel {
  String roomId;
  String otherUserId;
  String avatar;
  String name;
  String lastMessage;
  Timestamp lastMessageTime;

  RoomsListModel(
      {required this.roomId,
      required this.otherUserId,
      required this.avatar,
      required this.name,
      required this.lastMessage,
      required this.lastMessageTime});
}

class MyChatsScreen3 extends StatefulWidget {
  static const String id = "mychats3_screen";

  @override
  State<MyChatsScreen3> createState() => _MyChatsScreenState();
}

// get other user details
Future getOtherUser(String id) async {
  // get other user profile
  var user = await FirebaseFirestore.instance
      .collection("users")
      .doc(id)
      .get()
      .then((value) => value.data()) as Map<String, dynamic>;
  // return other user profile
  return user;
}

class _MyChatsScreenState extends State<MyChatsScreen3> {
  // get current user id
  String userId = AuthService().getUserId();

  // get all active chats
  **Stream<List>? roomsListStream() {**
    try {
      FirebaseFirestore.instance
          .collection("rooms")
          .where("users", arrayContains: userId)
          .orderBy("latestMessageTime", descending: true)
          .snapshots()
          .map((QuerySnapshot query) {
        List<RoomsListModel> retVal = [];
        query.docs.forEach((element) {
          retVal.add(RoomsListModel(
              roomId: element.id,
              otherUserId: element["users"][0] == userId
                  ? element["users"][1]
                  : element["users"][0],
              avatar: element["photoUrl"],
              name: element["name"],
              lastMessage: element["latestMessage"],
              **lastMessageTime: element["latestMessageTime"]**));
        });

        return retVal;
      });
    } catch (e) {
      print("Error: $e");
    }
  }

// List builder for mobile app
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SafeArea(
        // create listview of all chats of current user and show last message and other user name and photo
        child: **StreamBuilder(**
          stream: roomsListStream(),
          builder: (context, AsyncSnapshot<dynamic> snapshot) {
            **if (snapshot.hasData) {**
              return ListView.builder(
                itemCount: snapshot.data.length,
                itemBuilder: (context, index) {
                  return ListTile(
                    leading: CircleAvatar(
                        // show other user profile photo
                        //backgroundImage:
                        //NetworkImage(otherUser["profilePhotoUrl"]),
                        ),
                    //title: Text(snapshot.data[index]["userName"]),
                    subtitle: Text(snapshot.data[index]["lastMessage"]),
                  );
                },
              );
            } else {
              return Container(
                color: Colors.yellow,
              );
            }
          },
        ),
      ),
    );
  }
}

uj5u.com熱心網友回復：

你忘記await了FirebaseFirestore結果：

Stream<List>? roomsListStream() async* {
    try {
      var rooms = await FirebaseFirestore.instance
          .collection("rooms")
          .where("users", arrayContains: userId)
          .orderBy("latestMessageTime", descending: true)
          .snapshots();

      await rooms.map((QuerySnapshot query) async*{
        List<RoomsListModel> retVal = [];
        query.docs.forEach((element) {
          retVal.add(RoomsListModel(
              roomId: element.id,
              otherUserId: element["users"][0] == userId
                  ? element["users"][1]
                  : element["users"][0],
              avatar: element["photoUrl"],
              name: element["name"],
              lastMessage: element["latestMessage"],
              lastMessageTime: element["latestMessageTime"]));
        });

        yield retVal;
      });
    } catch (e) {
      print("Error: $e");
    }
  }

并改變這一點：

if (snapshot.hasData) {

對此：

if (snapshot.connectionState == ConnectionState.done && snapshot.hasData) {

標籤：Google Cloud Collective 安卓扑镖谷歌云火库

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