How to display list of data in application? - flutter

Question

I have encountered an error where the data is printed out in terminal but do not display in the application.
Future<DocumentSnapshot> getTeacher() async {
var firebaseUser = await FirebaseAuth.instance.currentUser;
var docRef = FirebaseFirestore.instance.collection("User");
var query = docRef.where("type", isEqualTo: "teacher").limit(10);
query.get().then((QuerySnapshot querySnapshot) {
querySnapshot.docs.forEach((doc) {
print(doc["name"]);
print(doc["email"]);
});
});
}
body: new FutureBuilder(
future: getTeacher(),
builder:
(BuildContext context, AsyncSnapshot<DocumentSnapshot> snapshot) {
if (snapshot.connectionState == ConnectionState.done) {
return ListView.builder(
shrinkWrap: true,
itemCount: 1,
itemBuilder: (BuildContext context, int index) {
return Row(
children: <Widget>[
Expanded(child: Text(snapshot.data["name"])),
Expanded(child: Text(snapshot.data["email"])),
Expanded(
child: IconButton(
icon: Icon(Icons.chat), onPressed: () {}))
],
);
});
}
return Container();
}),
this is the output in the terminal

Answer 1

Your getTeacher()-Function does not return your Future. Because of this
the Nullpointer-Exception ist thrown. You should return query.get() instead of listen to it.
You should also not call getTeacher() in the build-Function because it will be called at every build.
EDIT:
Your method:
Future<DocumentSnapshot> getTeacher() async {
var firebaseUser = await FirebaseAuth.instance.currentUser;
var docRef = FirebaseFirestore.instance.collection("User");
var query = docRef.where("type", isEqualTo: "teacher").limit(1);
return (await query.get()).docs[0];
}
Variable of your widget:
final Future<DocumentSnapshot> teacher = getTeacher();
Your FutureBuilder:
new FutureBuilder(
future: teacher,
builder: ...
)

Answer 2

You are not returning anything from future function. Please check below code
Future<List<DocumentSnapshot>> getTeacher() async {
var firebaseUser = await FirebaseAuth.instance.currentUser;
var docRef = FirebaseFirestore.instance.collection("users");
QuerySnapshot query =
await docRef.where("user_device_language", isEqualTo: "en").limit(10).get();
return query.docs;
}
And handle null value in list view like this
body: new FutureBuilder(
future: getTeacher(),
builder: (BuildContext context, AsyncSnapshot<List<DocumentSnapshot>> snapshot) {
if (snapshot.connectionState == ConnectionState.done) {
if (snapshot.data != null) {
return ListView.builder(
shrinkWrap: true,
itemCount: snapshot.data.length,
itemBuilder: (BuildContext context, int index) {
return Row(
children: <Widget>[
Expanded(child: Text(snapshot.data[index]["name"])),
Expanded(child: Text(snapshot.data[index]["email"])),
Expanded(child: IconButton(icon: Icon(Icons.chat), onPressed: () {}))
],
);
});
} else {
return Text('No Data');
}
}
return Container();
},
),