Question

我想创建一个聊天应用程序，我也使用过Firebase，但是我无法在发送消息时将文档排序与随机出现的列表顺序不一致的情况下对文档进行排序。

我认为这与firebase控制台中的文档类型有关（如果相关），我希望获得有关如何在收到新消息时对其进行排序的帮助，该消息将位于列表的底部，反之亦然。

我尝试了listview和listview.builder，并且使用了reverse属性，但它对我不起作用。

import 'package:flutter/material.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import '../constants.dart';

final _firestore = Firestore.instance;
FirebaseUser loggedInUser;

class ChatScreen extends StatefulWidget {
  static String routeName = 'chat_screen';

  @override
  _ChatScreenState createState() => _ChatScreenState();
}

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

  void getCurrentUser() async {
    try {
      final user = await _auth.currentUser();

      if (user != null) {
        loggedInUser = user;
      }
    } catch (e) {
      print(e);
    }
  }

  void getMessages() async {
    final messages = await _firestore.collection('message').getDocuments();
    for (var message in messages.documents) {
      print(message.data);
    }
  }

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

  @override
  void initState() {
    super.initState();

    getCurrentUser();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        leading: null,
        actions: <Widget>[
          IconButton(
              icon: Icon(Icons.close),
              onPressed: () {
                _auth.signOut();
                Navigator.pop(context);
              }),
        ],
        title: Text('⚡️Chat'),
        backgroundColor: Colors.lightBlueAccent,
      ),
      body: SafeArea(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.spaceBetween,
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: <Widget>[
            MessagesStream(),
            Container(
              decoration: kMessageContainerDecoration,
              child: Row(
                crossAxisAlignment: CrossAxisAlignment.center,
                children: <Widget>[
                  Expanded(
                    child: TextField(
                      controller: messageTextController,
                      onChanged: (value) {
                        message = value;
                      },
                      decoration: kMessageTextFieldDecoration,
                    ),
                  ),
                  FlatButton(
                    onPressed: () {
                      messageTextController.clear();
                      _firestore
                          .collection('messages')
                          .add({'text': message, 'sender': loggedInUser.email});
                    },
                    child: Text(
                      'Send',
                      style: kSendButtonTextStyle,
                    ),
                  ),
                ],
              ),
            ),
          ],
        ),
      ),
    );
  }
}

class MessagesStream extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return StreamBuilder<QuerySnapshot>(
      stream: _firestore.collection('messages').snapshots(),
      builder: (context, snapshot) {
        if (!snapshot.hasData) {
          return Center(
            child: CircularProgressIndicator(
              backgroundColor: Colors.lightBlueAccent,
            ),
          );
        }
        final messages = snapshot.data.documents;

        List<MessageBubble> messageBubbles = [];
        for (var message in messages) {
          final messageText = message.data['text'];
          final messageSender = message.data['sender'];
          final currentUser = loggedInUser.email;

          final messageBubble = MessageBubble(
              sender: messageSender,
              text: messageText,
              isMe: currentUser == messageSender);

          messageBubbles.add(messageBubble);
        }

        return Flexible(
          child: ListView.builder(
            itemCount: messages.length,
            itemBuilder: (context , index){
            return MessageBubble(
              isMe: loggedInUser.email == messages[index].data['sender'],
              text: messages[index].data['text'],
              sender: messages[index].data['sender'],
            );
          },),
        );
      },
    );
  }
}

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

  final bool isMe;
  final String sender;
  final String text;

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: EdgeInsets.all(10.0),
      child: Column(
        crossAxisAlignment:
            isMe ? CrossAxisAlignment.end : CrossAxisAlignment.start,
        children: <Widget>[
          Text(sender, style: TextStyle(fontSize: 12, color: Colors.black54)),
          Material(
              elevation: 5.0,
              borderRadius: isMe
                  ? BorderRadius.only(
                      topLeft: Radius.circular(30),
                      bottomLeft: Radius.circular(30),
                      topRight: Radius.circular(30),
                    )
                  : BorderRadius.only(
                      bottomLeft: Radius.circular(30),
                      topRight: Radius.circular(30),
                      bottomRight: Radius.circular(30)),
              color: isMe ? Colors.lightBlueAccent : Colors.white,
              child: Padding(
                padding: EdgeInsets.symmetric(vertical: 10, horizontal: 20),
                child: Text(
                  text,
                  style: TextStyle(
                      color: isMe ? Colors.white : Colors.black54,
                      fontSize: 15),
                ),
              )),
        ],
      ),
    );
  }
}

Answer 1

添加订单依据

void getMessages() async {
    final messages = await _firestore.collection('message').orderBy("created_at", descending: true).getDocuments();
    for (var message in messages.documents) {
      print(message.data);
    }
  }

  void messagesStream() async {
    await for (var snapshot in _firestore.collection('messages').orderBy("created_at", descending: true).snapshots()) {
      for (var message in snapshot.documents) {
        print(message.data);
      }
    }
  }

Answer 2

Cloud Firestore中没有文档的隐式排序。

如果要按特定顺序显示结果，则必须确保每个文档都包含必要的信息以确定其顺序。通常，这意味着您将在字段中添加创建文档的时间戳。

有了这样的字段，然后您可以使用orderBy()以特定的顺序检索文档：

await _firestore.collection('message').orderBy('timestamp').getDocuments()

Answer 3

选中此选项，可以在群聊应用中完美运行（如果您想从Firebase中获取数据）。

 class MessageStream extends StatelessWidget {


 @override

 Widget build(BuildContext context) {
 return StreamBuilder<QuerySnapshot>(

  stream: _firestore.collection("messages").orderBy("time").snapshots(),

  builder: (context, snapshot) {

    if (!snapshot.hasData) {

      return Center(
        child: CircularProgressIndicator(

          backgroundColor: Colors.amber,

        ),
      );
    }
    final messages = snapshot.data.documents.reversed;


    List<MessageBubble> messageBubbles = [];



    for (var message in messages) {

      final messageText = message.data["text"];

      final messageSender = message.data["sender"];

      final messageTime = message.data["time"];

      final currentUser = loggedInUser.email;


      final messageBubble = MessageBubble(

        sender: messageSender,

        text: messageText,

        isMe: currentUser == messageSender,

        time: messageTime,
      );
      messageBubbles.add(messageBubble);
    }
    return Expanded(

      child: ListView(

        reverse: true,
        padding: EdgeInsets.all(10),

        children: messageBubbles,
      ),
    );
  },
 );
 }
}

如何订购Firebase文件？

3 个答案: