使用 Dart/Flutter 连接到 Firebase 时，我的消息按时间顺序显示有一些问题。在 ListView 和查询 Firebase 时尝试反向顺序无济于事。
使用 Firebase Cloud Firestore 作为后端。我删除了firebase中的集合，将反向属性添加到数据检索和ListView中，但问题仍然存在。
我在 Firebase 中的数据库结构如下:
我可能需要设置一个整数属性和字段，以按消息出现的顺序显示消息，但不知道该怎么做。
以下是问题的屏幕截图和屏幕代码。
1、2、3、4应按时间顺序出现。
final _firestore = Firestore.instance;
FirebaseUser loggedInUser;
class ChatScreen extends StatefulWidget {
static const String id = 'chat_screen';
@override
_ChatScreenState createState() => _ChatScreenState();
}
class _ChatScreenState extends State<ChatScreen> {
final messageTextController = TextEditingController();
final _auth = FirebaseAuth.instance;
String messageText;
@override
void initState() {
super.initState();
getCurrentUser();
//retrieve the user credentials when screen is initialized
}
void getCurrentUser() async {
try {
final user = await _auth.currentUser();
// if somebody is logged in this will display to the current user
if (user != null) {
//if we do have a signed in user
loggedInUser = user;
//save the [logged in] user to the loggedInUser variable
}
} catch (e) {
print(e);
}
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
leading: null,
actions: <Widget>[
IconButton(
icon: Icon(Icons.close),
onPressed: () {
//Implement logout functionality
_auth.signOut();
//sign user out
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) {
messageText = value;
//store the entry value of the text entry field as the variable messageText
},
decoration: kMessageTextFieldDecoration,
),
),
FlatButton(
onPressed: () {
messageTextController.clear();
//clear the text field on button press
_firestore.collection('messages').add({
'text': messageText,
'sender': loggedInUser.email,
});
//log the information and values according to those established within Firebase
//retrieved from database collection and fields established in Firebase
},
child: Text(
'Send',
style: kSendButtonTextStyle,
),
),
],
),
),
],
),
),
);
}
}
class MessagesStream extends StatelessWidget {
@override
Widget build(BuildContext context) {
return StreamBuilder<QuerySnapshot>(
//StreamBuilder establishes the Stream of data pushed from Firebase console
//QuerySnapshot is the data type requested from the firebase console --> Querying a snapshot of the data housed in Firebase
stream: _firestore.collection('messages').snapshots(),
//the source of the stream should consist of the messages collection. Snapshots() performs the queries of the location to determine if there is anything new to push
builder: (context, snapshot) {
//build the stream to consist of the context and the snapshot query of the stream
if (!snapshot.hasData) {
//if the snapshot query returns null
return Center(
child: CircularProgressIndicator(),
//then display the circular progress indicator
);
}
final messages = snapshot.data.documents.reversed;
//store in the messages variable the query of the latest data [documents] posted to Firebase
List<MessageBubble> messageBubbles = [];
//establish a list (messageWidgets) to store the contents of the documents
for (var message in messages) {
//build for in loops to retrieve the data in messages storing to the variable message to call the data of each field within a document in the messages collection
final messageText = message.data['text'];
//retrieve the data stored in the text field and save to the variable messageText
final messageSender = message.data['sender'];
//retrieve the data stored in the sender field and save to the variable messageSender
final currentUser = loggedInUser.email;
final messageBubble = MessageBubble(
sender: messageSender,
text: messageText,
isMe: currentUser == messageSender,
);
//display the data retrieved from the data stored in the messageText and messageSender variables within the text and sender properties esatablished in the MessageBubble widget
messageBubbles.add(messageBubble);
//add each document data (messageWidget) retrieved and add it to the List messageWidgets
}
return Expanded(
//Expanded - limit to available space
child: ListView(
//make the area where this content is housed scrollable
reverse: true,
padding: EdgeInsets.symmetric(horizontal: 10.0, vertical: 20.0),
children: messageBubbles,
//return the data stored in messageWidgets
),
);
},
);
}
}
class MessageBubble extends StatelessWidget {
MessageBubble({
this.sender,
this.text,
this.isMe,
});
final String sender;
final String text;
//establish sender and text properties to further clarify where the data housed in the messageText and messageSender variables will be displayed
final bool isMe;
@override
Widget build(BuildContext context) {
return Padding(
padding: EdgeInsets.all(8.0),
child: Column(
crossAxisAlignment:
isMe ? CrossAxisAlignment.end : CrossAxisAlignment.start,
//if I am the logged in user that sent the message display the text bubble on the right, otherwise display on the left
children: <Widget>[
Text(
sender,
style: TextStyle(color: Colors.black54),
),
Material(
elevation: 5.0,
borderRadius: isMe
? BorderRadius.only(
topLeft: Radius.circular(30.0),
bottomLeft: Radius.circular(30.0),
bottomRight: Radius.circular(30.0),
)
: BorderRadius.only(
topRight: Radius.circular(30.0),
bottomLeft: Radius.circular(30.0),
bottomRight: Radius.circular(30.0),
),
//change the orientation of the border radius
color: isMe ? Colors.lightBlueAccent : Colors.white,
//if I am the logged in user that sent the message display the text bubble in light blue, otherwise display in white
child: Padding(
padding: EdgeInsets.symmetric(vertical: 10.0, horizontal: 15.0),
child: Text(
text,
style: TextStyle(
fontSize: 15.0,
color: isMe ? Colors.white : Colors.black,
//if I am the logged in user that sent the message display the text in white, otherwise display in black
),
),
),
),
],
),
);
}
}
最佳答案
在您的 Firestore 数据库中，为每个文档添加一个新的 int 键，并将其命名为 orderId并将值从 1 设置为 4。
然后改变这一行
_firestore.collection('messages').snapshots()
_firestore.collection('messages').orderBy('orderId', descending: true).snapshots()
orderId 订购的文件。 . descending: true意味着您希望它们从高阶到低阶。
关于firebase - 按时间顺序显示，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/62841285/