实时数据库 return 项目的 onValue 侦听器是否按照它们添加到数据库的顺序排列？

Question

我在任何地方的文档中都没有看到这一点。这个监听器 return 节点的数据是否按照添加到节点的顺序？例如，如果我添加 message1，然后是 message2，然后是 message3，此侦听器 return 数据的顺序是否与 message1、message2、message3 相同？

该应用程序使用一个名为 ChatScreen 的小部件来显示 ReceivedChats 小部件（聊天 body）和 MsgInput 小部件（聊天页脚）。没有聊天header（除非你算上应用栏？）。

ChatScreen 小部件：

class ChatScreen extends StatelessWidget {
  ChatScreen({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    final groupIDPath = 'groupChats/0exUS3P2XKFQ007TIMmm';
    return Scaffold(
      appBar: AppBar(
        leading: IconButton(
          icon: Icon(Icons.menu),
          color: Colors.white,
          onPressed: () {},
        ),
        title: Text(
          'Group Name',
        ),
        actions: [
          IconButton(
            icon: Icon(Icons.search),
            color: Colors.white,
            onPressed: () {},
          )
        ],
        backgroundColor: Color.fromRGBO(51, 50, 49, 1.0),
        elevation: 0.0,
      ),
      body: Column(
        children: [
          Expanded(
            flex: 11,
            child: Row(
              children: [
                Expanded(
                  child: ReceivedChats(groupIDPath: groupIDPath),
                ),
              ],
            ),
          ),
        ],
      )
    );
  }
}

ReceivedChats 小部件

class ReceivedChats extends StatefulWidget {
  const ReceivedChats({Key? key, required this.groupIDPath}) : super(key: key);
  final groupIDPath; 

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

class _ReceivedChatsState extends State<ReceivedChats> {
  late StreamSubscription _receivedChatsStream;
  final _database = FirebaseDatabase.instance.ref();

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


  void _activateListeners() {
    _receivedChatsStream = _database.child(groupIDPath).onValue.listen((event) {
      final data = event.snapshot.value;
      print('data: ' + data.toString()); //The data printed here is out of order
    });
  }

@override
  Widget build(BuildContext context) {

//...widget build stuff...//

   }
}

插入 RTDB：

class MessageDao {

  String groupIDPath; 
  DatabaseReference _messagesRef;
  FirebaseStorage _firebaseStorage;
  String _currentUID;

  MessageDao({required this.groupIDPath}):
        _messagesRef = FirebaseDatabase.instance.ref().child(groupIDPath),
        _firebaseStorage = FirebaseStorage.instance,
        _currentUID = FirebaseAuth.instance.currentUser!.uid.toString();

  //Save a single text message to RTDB
  void saveMessage(ChatData message) async {
    _messagesRef.push().set(message.toJson());
  }

RTDB中当前数据：

{
  "groupChats": {
    "0exUS3P2XKFQ007TIMmm": {
      "-N1HB8ik8RekJGQ-R9X-": {
        "filterID": "",
        "URL": "",
        "text": "1",
        "timestamp": "2022-05-04 22:08:20.782466",
        "type": "1",
        "uid": "f1JqanGGRtd709ia4mxgaM8Apn52"
      },
      "-N1HB9LQ-NAEzp3rNr4V": {
        "filterID": "",
        "URL": "",
        "text": "2",
        "timestamp": "2022-05-04 22:08:23.323476",
        "type": "1",
        "uid": "f1JqanGGRtd709ia4mxgaM8Apn52"
      },
      "-N1HDx2BAMNjio0o6gSU": {
        "filterID": "",
        "URL": "",
        "text": "3",
        "timestamp": "2022-05-04 22:20:35.275138",
        "type": "1",
        "uid": "f1JqanGGRtd709ia4mxgaM8Apn52"
      },
      "-N1HDxeB9V5mvb4i4w9o": {
        "filterID": "",
        "URL": "",
        "text": "4",
        "timestamp": "2022-05-04 22:20:37.772181",
        "type": "1",
        "uid": "f1JqanGGRtd709ia4mxgaM8Apn52"
      },
      "-N1HDy3jGshk_sLK4_oG": {
        "filterID": "",
        "URL": "",
        "text": "5",
        "timestamp": "2022-05-04 22:20:39.471453",
        "type": "1",
        "uid": "f1JqanGGRtd709ia4mxgaM8Apn52"
      },
      "-N1HEYpMpz4L6TMDLlgr": {
        "filterID": "",
        "URL": "",
        "text": "6",
        "timestamp": "2022-05-04 22:23:14.133822",
        "type": "1",
        "uid": "f1JqanGGRtd709ia4mxgaM8Apn52"
      },
      "-N1HE_be1sn86ZNu8KI5": {
        "filterID": "",
        "URL": "",
        "text": "7",
        "timestamp": "2022-05-04 22:23:21.450031",
        "type": "1",
        "uid": "f1JqanGGRtd709ia4mxgaM8Apn52"
      },
      "-N1HEaW0HDvCjqexapy4": {
        "filterID": "",
        "URL": "",
        "text": "8",
        "timestamp": "2022-05-04 22:23:25.121275",
        "type": "1",
        "uid": "f1JqanGGRtd709ia4mxgaM8Apn52"
      }
    }
  }
}

Answer 1

你问题中的相关代码是：

_database.child('groupChats/0exUS3P2XKFQ007TIMmm').onValue.listen((event) {
  final data = event.snapshot.value;
  print('data: ' + data.toString()); //The data printed here is out of order
})

由于您在 groupChats/0exUS3P2XKFQ007TIMmm 处的数据快照上调用 event.snapshot.value，您会在该路径上获得数据的 Map。根据定义，映射中的键是无序的。

如果你想处理子节点，按照它们在数据库中return的顺序，循环event.snapshot.children:

_database.child('groupChats/0exUS3P2XKFQ007TIMmm').onValue.listen((event) {
  event.snapshot.children.forEach((snapshot) {
    print('${snapshot.key}: ${snapshot.value}');
  })
})

如果你想return从数据库中以特定顺序获取子节点，调用orderBy...方法之一。例如，要按时间戳排序：

_database.child('groupChats/0exUS3P2XKFQ007TIMmm').orderByChild('timestamp').onValue.listen((event) {
  event.snapshot.children.forEach((snapshot) {
    print('${snapshot.key}: ${snapshot.value}');
  })
})

实时数据库 return 项目的 onValue 侦听器是否按照它们添加到数据库的顺序排列？

Does the onValue listener for Realtime Database return items in the same order that they are added to the database?

android

dart

firebase

firebase-realtime-database

flutter