The getter 'uid' was called on null - firebase

Question

Guys I have this login page with email and password and when the user is succesfully logged it takes him to a chatscreen. On the chatscreen I need to access users uid to check who is sending the message, but I am getting the "The getter 'uid' was called on null.". I am using bloc pattern to login with validators. How can I fix this situation?
class LoginScreen extends StatefulWidget {
FirebaseUser user;
#override
_LoginScreenState createState() => _LoginScreenState();
}
class _LoginScreenState extends State<LoginScreen> {
final _loginBloc = LoginBloc();
#override
void initState() {
super.initState();
_loginBloc.outState.listen((state) async {
switch (state) {
case LoginState.SUCCESS:
Navigator.of(context).pushReplacement(
MaterialPageRoute(builder: (context) => ComercialUserScreen()));
break;
case LoginState.FAIL:
showDialog(
context: context,
builder: (context) => AlertDialog(
title: Text('Erro'),
content: Text('Revise seu email e senha'),
));
break;
case LoginState.LOADING:
case LoginState.IDLE:
}
});
}
#override
Widget build(BuildContext context) {
return Scaffold(
body: StreamBuilder<LoginState>(
stream: _loginBloc.outState,
initialData: LoginState.LOADING,
// ignore: missing_return
builder: (context, snapshot) {
print(snapshot.data);
switch (snapshot.data) {
case LoginState.LOADING:
return Center(
child: CircularProgressIndicator(),
);
case LoginState.FAIL:
case LoginState.SUCCESS:
case LoginState.IDLE:
return Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
InputField(
icon: Icons.person_outline,
hint: 'Usuário',
obscure: false,
stream: _loginBloc.outEmail,
onChanged: _loginBloc.changeEmail,
),
InputField(
icon: Icons.lock_outline,
hint: 'Senha',
obscure: true,
stream: _loginBloc.outEmail,
onChanged: _loginBloc.changePassword,
),
SizedBox(
height: 32,
),
StreamBuilder<bool>(
stream: _loginBloc.outSubmitValid,
builder: (context, snapshot) {
return RaisedButton(
child: Text("Entrar"),
onPressed:
snapshot.hasData ? _loginBloc.submit : null,
);
})
],
);
}
}),
);
}
}
class LoginBloc extends BlocBase with LoginValidators{
FirebaseUser _currentUser;
final _emailController = BehaviorSubject<String>();
final _passwordController = BehaviorSubject<String>();
final _stateController = BehaviorSubject<LoginState>();
Stream<String> get outEmail => _emailController.stream.transform(validateEmail);
Stream<String> get outPassword =>_passwordController.stream.transform(validatePassword);
Stream<LoginState> get outState => _stateController.stream;
Stream<bool> get outSubmitValid => Observable.combineLatest2(
outEmail, outPassword, (a, b) => true);
Function(String) get changeEmail => _emailController.sink.add;
Function(String) get changePassword => _passwordController.sink.add;
StreamSubscription _streamSubscription;
LoginBloc(){
_streamSubscription = FirebaseAuth.instance.onAuthStateChanged.listen((user) async {
if(user != null) {
if(await verifyAdmins(user)) {
_stateController.add(LoginState.SUCCESS);
} else {
FirebaseAuth.instance.signOut();
_stateController.add(LoginState.FAIL);
}
} else {
_stateController.add(LoginState.IDLE);
}
});
}
void submit (){
final email = _emailController.value;
final password = _passwordController.value;
_stateController.add(LoginState.LOADING);
FirebaseAuth.instance.signInWithEmailAndPassword(
email: email,
password: password
).catchError((e) {
_stateController.add(LoginState.FAIL);
});
}
Future<bool> verifyAdmins (FirebaseUser user) async {
return await Firestore.instance.collection('users').document(user.uid).get().then((doc)
{
if(doc.data != null){
return true;
} else {
return false;
}
}).catchError((e) {
return false;
});
}
#override
void dispose() {
_emailController.close();
_passwordController.close();
_stateController.close();
_streamSubscription.cancel();
// TODO: implement dispose
}
}
class _AdminChatState extends State<AdminChat> {
bool _isLoading = false;
void _sendMessage({String text, File imgFile}) async {
DocumentSnapshot snapshot;
FirebaseUser user = await FirebaseAuth.instance.currentUser();
Map<String, dynamic> data = {
"uid" : user.uid,
'name' : user.displayName,
'photo' : user.photoUrl,
'time' : Timestamp.now()
};
if (imgFile != null){
StorageUploadTask task = FirebaseStorage.instance.ref().child('users').child(
DateTime.now().millisecondsSinceEpoch.toString()
).putFile(imgFile);
setState(() {
_isLoading = true;
});
StorageTaskSnapshot taskSnapshot = await task.onComplete;
String url = await taskSnapshot.ref.getDownloadURL();
data['imgUrl'] = url;
setState(() {
_isLoading = false;
});
}
if(text != null) data["text"] = text;
Firestore.instance.collection("users").document(snapshot.documentID)
.collection('messages').add(data);
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('hello'),
),
body: Column(
children: <Widget>[
Expanded(
child: StreamBuilder<QuerySnapshot>(
stream:
Firestore.instance.collection('users').document(widget.snapshot.documentID)
.collection('messages').orderBy('time').snapshots(),
builder: (context, snapshot){
switch(snapshot.connectionState) {
case ConnectionState.none:
case ConnectionState.waiting:
return Center(
child: CircularProgressIndicator(),
);
default:
List<DocumentSnapshot> documents =
snapshot.data.documents.reversed.toList();
return ListView.builder(
itemCount: documents.length,
reverse: true,
itemBuilder: (context, index){
// ignore: unrelated_type_equality_checks
return ChatMessage(documents[index].data, true);
});
}
},
),
),
_isLoading ? LinearProgressIndicator() : Container(),
TextComposer(_sendMessage),
],
),
);
}
}

Answer 1

The command await FirebaseAuth.instance.currentUser(); in the _AdminChatState doesn't return any data so when you try to insert data based on the user is returns null. This happens because you can't use await while the state hasn't initialized. If that happened the entire class would wait with nothing show until the user was returned. Furthermore, you use a storage query with the same logic. If you want a state widget to run something when it starts up you can use the initState() function. If you want do display a progress bar while waiting for the data to return a FutureBuilder or StreamBuilder are great choices.