Flutter：流不會自動更新資料（僅在熱多載后）

問題：下面代碼中的兩個流都不會自動更新我的 UI。因此，僅在我進行熱多載或熱重啟時才會獲取并顯示新資料。我正在嘗試從每個聊天室獲取最新訊息并將其顯示給用戶。

問題：如何更改我的代碼以使流正常作業？或者對我在下面做的事情可能有更好的解決方案？

    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';

class MyChatsScreen2 extends StatelessWidget {
  static const String id = "mychats2_screen";

  // get current user id
  String? userId = AuthService().getUserId();

  // Stream of all rooms of current user
  Stream getRoomsStream() async* {
    // get rooms of current user
    QuerySnapshot roomsSnapshot = await FirebaseFirestore.instance
        .collection("rooms")
        .where("userId1", isEqualTo: userId)
        .get();
    // get rooms of current user
    QuerySnapshot roomsSnapshot2 = await FirebaseFirestore.instance
        .collection("rooms")
        .where("userId2", isEqualTo: userId)
        .get();
    // add rooms of current user to rooms list
    List<QueryDocumentSnapshot> rooms = roomsSnapshot.docs;
    // add rooms of current user to rooms list
    List<QueryDocumentSnapshot> rooms2 = roomsSnapshot2.docs;
    // add rooms of current user to rooms list
    rooms.addAll(rooms2);
    // sort rooms list by when last message was sent
    // rooms.sort(
    // (a, b) => b["lastMessageSentAt"].compareTo(a["lastMessageSentAt"]));
    yield rooms;
  }

  // Stream to get last message of each room
  Stream getLastMessageStream(String roomId) async* {
    try {
      // get last message of room
      QuerySnapshot lastMessageSnapshot = await FirebaseFirestore.instance
          .collection("rooms")
          .doc(roomId)
          .collection("messages")
          .orderBy("createdAt", descending: true)
          .limit(1)
          .get();
      // get last message of room
      List lastMessage = lastMessageSnapshot.docs;
      // return last message of room
      yield lastMessage;
    } catch (error) {
      print(error);
    }
  }

  @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: getRoomsStream(),
          builder: (context, AsyncSnapshot<dynamic> snapshot) {
            if (snapshot.hasData) {
              return ListView.builder(
                itemCount: snapshot.data.length,
                itemBuilder: (context, index) {
                  return StreamBuilder(
                    stream: getLastMessageStream(snapshot.data[index].id),
                    builder: (context, AsyncSnapshot<dynamic> snapshot2) {
                      if (snapshot2.hasData) {
                        return ListTile(
                          leading: CircleAvatar(
                              //backgroundImage: NetworkImage(
                              //snapshot.data[index]["userPhotoUrl"]),
                              ),
                          //title: Text(snapshot.data[index]["userName"]),
                          subtitle: Text(snapshot2.data[0]["message"]),
                        );
                      } else {
                        return Container();
                      }
                    },
                  );
                },
              );
            } else {
              return Container();
            }
          },
        ),
      ),
    );
  }
}

uj5u.com熱心網友回復：

由于您在get()創建小部件時使用，因此僅在創建小部件時從資料庫中加載一次資料。如果您想在更新時獲取新資料，請使用snapshot()偵聽器 - 它回傳一個流，該流使用初始資料獲取初始事件，并在資料更新時獲取新事件。

要Stream在您的build方法中連接起來，您需要使用StreamBuilderFirebase 檔案中關于在 Flutter 中偵聽實時更新的說明。

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