[英]The body might complete normally, causing 'null' to be returned, but the return type, is a potentially non-nullable type
[英]error: The body might complete normally, causing 'null' to be returned, but the return type is a non-nullable type
我正在使用 FireBase 構建一個 flashChat 應用程序。它基本上是一個可用於發送消息的聊天應用程序。消息存儲在 FireBase 集合中。我們必須檢索消息並將其顯示在屏幕上。
要顯示內容(快照),我正在使用 Streams。 我收到以下錯誤
錯誤:正文可能正常完成,導致返回“null”,但返回類型可能是不可為空的類型。 (body_might_complete_normally 在 [flashchat1] lib\screens\chat_screen.dart:80)
這是我的代碼:-
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,
),
),
],
),
),
],
),
),
);
}
}
當 if 條件未解決時,您不會在 StreamBuilder 中返回任何內容...
只需添加一個其他的,比如... SizedBox.shrink()
或任何你需要的
或者返回一個空Column
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