錯誤使用父 Widget

Question

我正在嘗試制作一個 flash 聊天應用程序，它從 fireBase 檢索聊天並將其顯示在屏幕上。我將它包裝在一個擴展小部件下。我已經給它一些填充。 我收到以下錯誤

查找父數據時引發了以下斷言。：ParentDataWidget 的使用不正確。

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flashchat1/constants.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
class ChatScreen extends StatefulWidget {
  static String id='Chat_Screen';
  @override
  _ChatScreenState createState() => _ChatScreenState();
}

class _ChatScreenState extends State<ChatScreen> {
  final _fireStore = FirebaseFirestore.instance;//an instance of fireBase store that stored data created
  final _auth = FirebaseAuth.instance;//instance/object of fireBase auth that authorizes users is created
  late User loggedInUser;//LoggedInUser is of type FireBase user(now changed to user)
  late String messageText;
  @override
  void initState()
  {
    super.initState();
    getCurrentUser();//calling the getCurrentUser
  }
  void getCurrentUser()
  async{
    try
    {
      final user= await _auth.currentUser;//get the current user id/name/email.Also currentUser return a future so make it async by adding await and async keywords
      if(user!=null)
      {
        loggedInUser=user ;//LoggedInUser = user contains email of the info
        print(loggedInUser.email);
      }

    }
    catch(e)
    {
      print(e);
    }
  }// Under collection there is documents.Inside documents there are fields like type ,values etc.These fields contain our information
    Future<void> messageStream()//Using a stream it becomes very easy .U just need to click once after you run the app .Then u will be done.
    async {//The snapShot here is FireBase's Query SnapShot
      await for(var snapshot in _fireStore.collection('messages').snapshots()){//make a variable snapshot to store the entire items of the collection in fireBase (Look at the fireBase console there is a collection called messages).This collection takes the snapshot of all the iteams (not literal snapshot .Think it like a snapShot)
        for(var message in snapshot.docs)//make a variable message to access the snapShot.docs .(docs stands for Documentation.Look at the fireBase console)
        print(message.data());
      }
    }
  void getMessages()//(The problem with this is that we need to keep clicking on the onPressed button every single time the new message is sent .So it is not convinient
  async {
    final messages = await _fireStore.collection('messages').get();//to retrieve the data from fire base we are creating a variable message
   messages.docs;//retreive the data from document section under the collection in firestore
    for(var message in messages.docs)//since it is a messages.docs is a list we need to loop through it
       {
        print(message.data());//print the data its messge.data()
     }
  }
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        leading: null,
        actions: <Widget>[
          IconButton(
              icon: Icon(Icons.close),
              onPressed: () {
                messageStream();
                //_auth.signOut();
                //Navigator.pop(context);
                //Implement logout functionality
              }),
        ],
        title: Text('⚡️Chat'),
        backgroundColor: Colors.lightBlueAccent,
      ),
      body: SafeArea(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.spaceBetween,
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: <Widget>[
            Expanded(
              child: StreamBuilder(
                stream:_fireStore.collection('messages').snapshots(),
                builder: (context, AsyncSnapshot snapshot) {
                  //This is Flutter's Async snapShot
                  //if(!snapshot.data)
                   // {
                     // return Center(
                      //child:  CircularProgressIndicator(
                        //backgroundColor:Colors.lightBlueAccent,
                      //),
                      //);
                    //}
                  if(!snapshot.hasData){//flutters async snapshot contains a query snapshot
                    return Center(
                    child:CircularProgressIndicator(
                    backgroundColor:Colors.lightBlueAccent,
                ),
                      );
                    }
                    final messages = snapshot.data.docs;
                    List<Text> messageWidgets = [];
                    for(var  message in messages)//Loop through the messages
                      {
                        final messageText = message.data()['text'];//retrieve the data under the text field in message collection
                        final messageSender = message.data()['Sender'];//retrieve the data under the Sender field in message collection
                        final messageWidget = Text('$messageText from $messageSender',
                        style:TextStyle(
                          fontSize:50,
                        ),
                        );
                        messageWidgets.add(messageWidget);//add the text to the List messageWidget
                        }
                        return Expanded(
                          flex:2,
                          child: ListView(//changed from Column to ListView as we want to scroll down .Or else only finite messages can be fit
                            children: messageWidgets, //if u don't write else with a return it will show an error as null returned and null safety broken
                            padding: EdgeInsets.symmetric(horizontal: 5,vertical: 5),
                          ),
                        );
                  },
              ),
            ),
            Container(
              decoration: kMessageContainerDecoration,
              child: Row(
                crossAxisAlignment: CrossAxisAlignment.center,
                children: <Widget>[
                  Expanded(
                    child: TextField(
                      onChanged: (value) {
                        messageText=value;//Whatever you chat will be stored in the variable String variable messageText
                      },
                      decoration: kMessageTextFieldDecoration,
                    ),
                  ),
                  FlatButton(
                    onPressed: () {
                      _fireStore.collection('messages').add({
                        'text': messageText,//add the messages sent to fireStore under the messages object that we created manually
                        'Sender': loggedInUser.email,//add the current users email to the sender field
                      },);
                    },//goal is to send the data that we type here to the fireStore cloud
                    child: Text(
                      'Send',
                      style: kSendButtonTextStyle,
                    ),
                  ),
                ],
              ),
            ),
          ],
        ),
      ),
    );
  }
}

Answer 1

 return Expanded(
                      flex:2,
                      child: ListView(//changed from Column to ListView as we want to scroll down .Or else only finite messages can be fit
                        children: messageWidgets, //if u don't write else with a return it will show an error as null returned and null safety broken
                        padding: EdgeInsets.symmetric(horizontal: 5,vertical: 5),
                      ),
                    );

這個代碼塊就是這里的問題。 您不能在任何您喜歡的地方使用擴展小部件。 Expanded 小部件只能在Row或Column小部件內使用。

刪除上面代碼塊中的 Expanded 小部件。 它會起作用。