错误：主体可能正常完成，导致返回“null”，但返回类型是不可为空的类型

Posted 2023-04-19

【中文标题】错误：主体可能正常完成，导致返回“null”，但返回类型是不可为空的类型

【英文标题】：error: The body might complete normally, causing 'null' to be returned, but the return type is a non-nullable type

【发布时间】：2021-11-21 05:15:36

【问题描述】：

我正在使用 FireBase 构建一个 flashChat 应用程序。它基本上是一个可用于发送消息的聊天应用程序。消息存储在 FireBase 集合中。我们必须检索并在屏幕上显示消息。

为了显示内容（快照），我正在使用 Streams 。 我收到以下错误

错误：主体可能正常完成，导致返回“null”，但返回类型可能是不可为空的类型。 （body_might_complete_normally at [flashchat1] lib\screens\chat_screen.dart:80）

这是我的代码：-

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.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 users
        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>[
            StreamBuilder(
              stream:_fireStore.collection('messages').snapshots(),
              builder: (context, AsyncSnapshot snapshot) //This is Flutter's Async snapShot
                if(snapshot.hasData)//flutters async snapshot contains a query snapshot
                  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');
                      messageWidgets.add(messageWidget);
                      
                      return Column(
                        children: messageWidgets,
                      );
                    
                ,
            ),
            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,
                    ),
                  ),
                ],
              ),
            ),
          ],
        ),
      ),
    );
  
 

【参考方案1】：

当 if 条件未解决时，您不会在 StreamBuilder 中返回任何内容...

只需添加一个 else，比如...SizedBox.shrink() 或任何你需要的东西

或者返回一个空的Column