A non-null String must be provided to a Text widget flutter - firebase

Question

I have this problem with this code. I tried to solve the problem, but I did not succeed. Please Help
Please see the screenshots to understand the problem well
A non-null String must be provided to a Text widget.
'package:flutter/src/widgets/text.dart':
Failed assertion: line 370 pos 10: 'data != null'
Pictures description error
null in firebase
The users email address.Will be null if signing in anonymously.
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';
import 'package:flash_chat/constants.dart';
class ChatScreen extends StatefulWidget {
static const Id = 'chat_screen';
#override
_ChatScreenState createState() => _ChatScreenState();
}
class _ChatScreenState extends State<ChatScreen> {
// ignore: deprecated_member_use
final _firestore = Firestore.instance;
final _auth = FirebaseAuth.instance;
// ignore: deprecated_member_use
FirebaseUser loggedInUser;
String messageText;
#override
void initState() {
super.initState();
getCurrentUser();
}
void getCurrentUser() async {
try {
// ignore: await_only_futures
final user = await _auth.currentUser;
if (user != null) {
loggedInUser = user;
print(loggedInUser.email);
}
} catch (e) {
print(e);
}
}
// void getMessages() async {
// // ignore: deprecated_member_use
// final messages = await _firestore.collection('Messages').getDocuments();
// // ignore: deprecated_member_use
// for (var message in messages.docs) {
// print(message.data());
// }
// }
void messagesStream() async {
await for (var snapshot in _firestore.collection('Messages').snapshots()) {
for (var message in snapshot.docs) {
print(message.data());
}
}
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
leading: null,
actions: <Widget>[
IconButton(
icon: Icon(Icons.close),
onPressed: () {
messagesStream();
//_auth.signOut();
//Navigator.pop(context);
}),
],
title: Text('⚡️Chat'),
backgroundColor: Colors.lightBlueAccent,
),
body: SafeArea(
child: Column(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
StreamBuilder<QuerySnapshot>(
stream: _firestore.collection('Messages').snapshots(),
// ignore: missing_return
builder: (context, snapshot) {
if (!snapshot.hasData) {
return Center(
child: CircularProgressIndicator(
backgroundColor: Colors.lightBlueAccent,
));
}
// ignore: deprecated_member_use
final messages = snapshot.data.documents;
List<Messagebubble> messagebubbles = [];
for (var message in messages) {
final messageText = message.data()['text'];
final messagesendar = message.data()['Sender'];
final messagebubble = Messagebubble(
sendar: messagesendar,
text: messageText,
);
messagebubbles.add(messagebubble);
}
return Expanded(
child: ListView(
padding: EdgeInsets.symmetric(
horizontal: 10.0,
vertical: 20.0,
),
children: messagebubbles,
),
);
},
),
Container(
decoration: kMessageContainerDecoration,
child: Row(
crossAxisAlignment: CrossAxisAlignment.center,
children: <Widget>[
Expanded(
child: TextField(
onChanged: (value) {
messageText = value;
},
decoration: kMessageTextFieldDecoration,
),
),
FlatButton(
onPressed: () {
_firestore.collection('Messages').add({
'text': messageText,
'Sender': loggedInUser,
});
},
child: Text(
'Send',
style: kSendButtonTextStyle,
),
),
],
),
),
],
),
),
);
}
}
class Messagebubble extends StatelessWidget {
Messagebubble({
Key key,
this.sendar,
this.text,
}) : super(key: key);
final String sendar;
final String text;
#override
Widget build(BuildContext context) {
return Padding(
padding: EdgeInsets.all(10.0),
child: Column(
children: [
Text(
sendar,
style: TextStyle(
fontSize: 12.0,
color: Colors.black54,
),
),
Material(
borderRadius: BorderRadius.circular(30.0),
elevation: 5.0,
color: Colors.lightBlueAccent,
child: Padding(
padding: EdgeInsets.symmetric(
vertical: 10.0,
horizontal: 20.0,
),
child: Text(
text,
style: TextStyle(
color: Colors.white,
fontSize: 15.0,
),
),
),
),
],
),
);
}
}

Answer 1

You just need to check whether the text that you are passing is null or not. If it is null, you can show that the user is Anonymous.
final messageText = message.data()['text'];
final messagesendar = message.data()['Sender'] ?? 'Anonymous'; // If null then use 'Anonymous'
final messagebubble = Messagebubble(
sendar: messagesendar,
text: messageText,
);
Flutter doesn't allow you to pass null to Text widgets.