firebase flutter - Receive null till reload emulator works fine - firebase

Question

Is there anyway to avoid Streambuilder or Futurebuilder for query data from firebase. I have tried to use Future async but error said received null till I reload the emulator after that it works fine.
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';
class infoStudentCard extends StatefulWidget {
infoStudentCard();
#override
_infoStudentCardState createState() => _infoStudentCardState();
}
class _infoStudentCardState extends State<infoStudentCard> {
String userId = (FirebaseAuth.instance.currentUser).uid;
String _sname;
String _slastname;
String _semail;
String _sid;
String _sclass;
Future data;
#override
void initState() {
super.initState();
data = getDataFromDb();
}
Future<void> getDataFromDb() async{
FirebaseFirestore.instance
.collection("student")
.doc(userId)
.get()
.then((DocumentSnapshot documentSnapshot) {
this._sname = documentSnapshot.get('sname');
});
}
#override
Widget build(BuildContext context) {
return Text(_sname);
}
}

Answer 1

received null till I reload the emulator after that it works fine.
Everytime you change something, call setState to see the result:
Future<void> getDataFromDb() async{
FirebaseFirestore.instance
.collection("student")
.doc(userId)
.get()
.then((DocumentSnapshot documentSnapshot) {
setState(() {
this._sname = documentSnapshot.get('sname');
});
});
}
Other, inside the initState, you are calling data = getDataFromDb but, your function return nothing. Just add:
#override
void initState() {
super.initState();
getDataFromDb();
}
or add a value to your data returning a value from function
late Future<DocumentSnapshot> data;
#override
void initState() {
super.initState();
data = getDataFromDb();
}
Future<DocumentSnapshot > getDataFromDb() async{
return FirebaseFirestore.instance
.collection("student")
.doc(userId)
.get()
.then((DocumentSnapshot documentSnapshot) {
setState(() {
this._sname = documentSnapshot.get('sname');
});
});
}