流未返回任何值

Question

我有一个流显然不返回值。我在Streambuilder中使用的快照没有返回任何内容，而是返回黄色容器(请参阅下面的代码(，当我的快照没有数据时，会返回该容器。知道这个问题的原因吗？

下面你会看到所有的函数，流以及我的Streambuilder。

这是更新后的流。otherUserId打印语句未打印。也许错误就在这里。

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,
);
}
},
),
),
);
}
}

Answer 1

对于FirebaseFirestore结果，您忘记了await：

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");
}
}

并改变这个：

if (snapshot.hasData) {

到此：

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