Flutter StreamBuilder小部件錯誤：類型'（）=&gt; Map<string, dynamic> ' 不是類型 'DocumentSnapshot 的子類型<object?> ' 在類型轉換中</object?></string,>

Question

錯誤：類型“() => Map<String, dynamic >”不是類型轉換中“DocumentSnapshot<Object?>”類型的子類型。

下面是我的聊天屏幕的代碼示例，它是我的聊天應用程序的主要組件之一，我想使用 firebase 構建消息的 stream 消息，但這給出了一個錯誤應用程序在此屏幕之前完全正常工作，但在此屏幕之后它會拋出一個錯誤請幫我解決這個問題，我正在使用 Streambuilder 小部件，請查看它

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_core/firebase_core.dart';
import 'package:flutter/material.dart';
import 'package:lets_chat/constant.dart';
import 'package:firebase_auth/firebase_auth.dart';

//final _firestore = FirebaseFirestore.instance;
//FirebaseUser = loggedInUser;

late User loggedInUser;

class ChatScreen extends StatefulWidget {
  static const String id3 = 'chat_screen';
  @override
  _ChatScreenState createState() => _ChatScreenState();
}

class _ChatScreenState extends State<ChatScreen> {
  final messageTextController = TextEditingController();
  final _fireStore = FirebaseFirestore.instance;
  final _auth = FirebaseAuth.instance;

  late String messageText;

  @override
  void initState() {
    // TODO: implement initState
    super.initState();

    getCurrentUser();
  }

  void getCurrentUser() async {
    try {
      final user = await _auth.currentUser;
      if (user != null) {
        loggedInUser = user;
      }
    } catch (e) {
      print(e);
    }
  }

  void messagesStream() async {
    await for (var snapshot in _fireStore.collection('messages').snapshots()) {
      for (var messages in snapshot.docs) {
        print(messages.data);
      }
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        leading: null,
        actions: <Widget>[
          IconButton(
              icon: Icon(Icons.close),
              onPressed: () {
                //Implement logout functionality
              }),
        ],
        title: Text('⚡️Chat'),
        backgroundColor: Colors.lightBlueAccent,
      ),
      body: SafeArea(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.spaceBetween,
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: <Widget>[
            StreamBuilder<QuerySnapshot>(
              stream: _fireStore.collection('messages').snapshots(),
              builder: (context, snapshot) {
                if (!snapshot.hasData) {
                  return Center(
                    child: CircularProgressIndicator(),
                  );
                }
                final messages = snapshot.data?.docs;
                List<MessageBubble> messageBubbles = [];
                for (var message in messages!) {
                  final messageText =
                      (message.data as DocumentSnapshot)['text'];
                  final messageSender =
                      (message.data as DocumentSnapshot)['sender'];

                  final currentUser = loggedInUser.email;

                  final messageBubble = MessageBubble(
                    sender: messageSender,
                    text: messageText,
                    loggedUser: currentUser == messageSender,
                  );
                  messageBubbles.add(messageBubble);
                }
                return Expanded(
                  child: ListView(
                    children: messageBubbles,
                  ),
                );
              },
            ),
            Container(
              decoration: kMessageContainerDecoration,
              child: Row(
                crossAxisAlignment: CrossAxisAlignment.center,
                children: <Widget>[
                  Expanded(
                    child: TextField(
                      controller: messageTextController,
                      onChanged: (value) {
                        messageText = value;
                      },
                      decoration: kMessageTextFieldDecoration,
                    ),
                  ),
                  TextButton(
                    onPressed: () {
                      _fireStore.collection('messages').add({
                        'text': messageText,
                        'sender': loggedInUser.email,
                      });
                    },
                    child: Text(
                      'Send',
                      style: kSendButtonTextStyle,
                    ),
                  ),
                ],
              ),
            ),
          ],
        ),
      ),
    );
  }
}

class MessageBubble extends StatelessWidget {
  MessageBubble(
      {required this.sender, required this.text, required this.loggedUser});

  final String sender;
  final String text;
  final bool loggedUser;

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: EdgeInsets.all(10.0),
      child: Column(
        crossAxisAlignment: CrossAxisAlignment.end,
        children: [
          Text(
            'sender',
            style: TextStyle(
              color: Colors.pink,
            ),
          ),
          Material(
              elevation: 5.0,
              borderRadius: BorderRadius.only(
                  topLeft: Radius.circular(20.0),
                  bottomLeft: Radius.circular(20.0),
                  bottomRight: Radius.circular(20.0)),
              color: loggedUser
                  ? Colors.pinkAccent.shade200
                  : Colors.blueAccent.shade200,
              child: Padding(
                  padding:
                      EdgeInsets.symmetric(vertical: 10.0, horizontal: 10.0),
                  child: Text('$text from $sender'))),
        ],
      ),
    );
  }
}

Answer 1

您的代碼的問題是您正在嘗試將message.data as DocumentSnapshot ，它試圖將() => Map<String, dynamic> （由.data返回）轉換為DocumentSnapshot ，這是不正確的。

message是一個QuerySnapshot ，您需要使用data()方法來訪問這些字段。

final messages = snapshot.data?.docs;
List<MessageBubble> messageBubbles = [];
for (var message in messages!) {
  final messageText = message.data()['text'];
  final messageSender = message.data()['sender'];
  // ...
}