The argumnet type 'Null Funcion(DataSnapshot)' cnt be assigned to the parameter type 'Future Or <dynamic> Function(DataBaseEvent)' - firebase

Question

I have this function that is giving me an error.
the getCurrentOnLineUserInfo function is trying to get read data from the Firebase Database of the current user that is logged in.
The argument type 'Null Funcion(DataSnapshot)' can't be assigned to the parameter of type 'Future Or Function(DataBaseEvent)'
I am following a year-old tutorial, so the issue might be the code is old. I might need new syntax or something.
static void getCurrentOnLineUserInfo() async {
firebaseUser = await FirebaseAuth.instance.currentUser;
String userId = firebaseUser!.uid;
DatabaseReference reference =
FirebaseDatabase.instance.ref().child("user").child(userId);
print("getCurrentOnLineUser info executed!");
print('${firebaseUser!.email}${firebaseUser!.displayName}');
// errors below this
reference.once().then((DataSnapshot dataSnapshot) {
if (dataSnapShot!.value != null) {
userCurrentInfo = Users.fromSnapshot(dataSnapshot);
}
});
}
}
and here is my class that is assigning data. This class is giving no errors
class Users {
String? id;
String? email;
String? phone;
String? name;
Users({this.id, this.email, this.phone, this.name});
Users.fromSnapshot(DataSnapshot dataSnapshot) {
id = dataSnapshot.key!;
var data = dataSnapshot.value as Map?;
if (data != null) {
email = data?["email"];
name = data?["name"];
phone = data?["phone"];
}
}
}

Answer 1

The once method returns a DatabaseEvent, not a DataSnapshot. DatabaseEvent is a class that encapsulates a DataSnapshot AND a DatabaseEventType, to extract the snapshot, you must use DatabaseEvent.snapshot:
reference.once().then((event) {
final dataSnapshot = event.snapshot;
if (dataSnapShot!.value != null) {
userCurrentInfo = Users.fromSnapshot(dataSnapshot);
}
});
Here is another solution I think might do what you want:
// async methods should return a future
static Future<void> getCurrentOnLineUserInfo() async {
firebaseUser = await FirebaseAuth.instance.currentUser;
String userId = firebaseUser!.uid;
DatabaseReference reference =
FirebaseDatabase.instance.ref().child("user").child(userId);
final snapshot = await reference.get(); // you should use await on async methods
if (snapshot!.value != null) {
userCurrentInfo = Users.fromSnapshot(snapshot);
}
}
}

Answer 2

I was following the same old tutorial you mentioned, the #mobdev991 answer is correct and i think the reason why you don't receive data is the class where you are assigning data try this
class Users {
String? id;
String? email;
String? name;
String? phone;
Users({this.id, this.email, this.name, this.phone});
Users.fromSnapshot(DataSnapshot dataSnapshot) {
id = dataSnapshot.key;
email = (dataSnapshot.child("email").value.toString());
name = (dataSnapshot.child("name").value.toString());
phone = (dataSnapshot.child("phone").value.toString());
}
}