DocumentSnapshot Listener - flutter

Question

I have a question how do i listen to real-time changes to a document snapshot based on the email of the currentUser in a initState. I knew that QuerySnapshot will need to use documents.forEach to be able to retrieve but how about DocumentSnapshot. This is my code:
#override
void initState() async{
FirebaseUser user = await FirebaseAuth.instance.currentUser();
Firestore.instance.collection('user').document(user.email).snapshots()
.listen((userinfo){
userinfo((userI){
_fname = userI.data['FullName'];
_SSID = userI.data['SSID'];
_email = userI.data['email'];
_image = userI.data['image'];
});
});
super.initState();
}
I am able to get the user.email but not able to listen to the Firestore. I can't really find anything that is similar to this maybe it's a relatively easy problem to solve for I'm still new to Flutter and Firebase. Thank you in advance.

Answer 1

It should be userI.data()['some_key'] instead of userI.data['some_key'].
https://pub.dev/documentation/cloud_firestore/latest/cloud_firestore/DocumentSnapshot/data.html
Also reomve userInfo, it should be like this:
Firestore.instance.collection('user').document(user.email).snapshots().listen((userI) {
_fname = userI.data()['FullName'];
_SSID = userI.data()['SSID'];
_email = userI.data()['email'];
_image = userI.data()['image'];
});

Answer 2

You can move your asynchronous logic into a different function and call it in your initState like this:
#override
void initState() {
super.initState();
_getUserData();
}
Future<void> _getUserData() async {
FirebaseUser user = await FirebaseAuth.instance.currentUser();
Firestore.instance.collection('user').document(user.email).snapshots()
.listen((userinfo) {
setState((){
_fname = userinfo.data['FullName'];
_SSID = userinfo.data['SSID'];
_email = userinfo.data['email'];
_image = userinfo.data['image'];
});
});
}
And in the widget where you use the variables, you can easily add a null check and display an empty value or a loading indicator.
Text(_fname??'')
or
_fname == null ? Center(child: CircularProgressIndicator()) : Text(_fname)