Flutter - widget variables are always null - firebase

Question

I have a Flutter app connected to firebase, and I'm using it to receive push notifications from Firebase Cloud Messaging, using this code. Whenever I call the variables widget.title, widget.body, they are null, but when the method receives a notification, they have the value that came from FCM. What should I do?
class PushList extends StatefulWidget {
Map<dynamic, dynamic> notific;
String title, body;
Future<dynamic> fcmMessageReceiver() async {
FirebaseMessaging.instance.getInitialMessage().then((value) {
if (value != null) {}
});
FirebaseMessaging.onMessage.listen((RemoteMessage message) {
if (message.notification != null) {
notificacao = {
'title': message.notification.title,
'body': message.notification.body
};
title = message.notification.title;
body = message.notification.body;
print('MENSAGEM: $notific');
}
});
FirebaseMessaging.onMessageOpenedApp.listen((RemoteMessage message) {});
}
PushList() {
}
#override
_PushListState createState() => _PushListState();
}
class _PushListState extends State<PushList> {
#override
Widget build(BuildContext context) {
return Scaffold(
extendBody: true,
backgroundColor: Colors.white,
appBar: null,
body: ListView(
children: [
widget.notific != null
? Card(
margin: EdgeInsets.all(10),
elevation: 4,
child: ListTile(
title: Text(
widget.title,
),
subtitle: Text(
widget.body,
),
),
)
: Container(
child: Text("U don't have new notifcs."),
),
],
),
);
}
}

Answer 1

PushList should be immutable. Define the properties inside the state and call fcmMessageReceiver inside initState. Also you need to call setState to trigger rebuild after you set title and body:
class PushList extends StatefulWidget {
#override
_PushListState createState() => _PushListState();
}
class _PushListState extends State<PushList> {
Map<dynamic, dynamic> notific;
String title, body;
#override
void initState() {
super.initState();
fcmMessageReceiver();
}
Future<dynamic> fcmMessageReceiver() async {
FirebaseMessaging.instance.getInitialMessage().then((value) {
if (value != null) {}
});
FirebaseMessaging.onMessage.listen((RemoteMessage message) {
if (message.notification != null) {
if (mounted) {
setState(() {
notificacao = {
'title': message.notification.title,
'body': message.notification.body
};
title = message.notification.title;
body = message.notification.body;
});
}
print('MENSAGEM: $notific');
}
});
FirebaseMessaging.onMessageOpenedApp.listen((RemoteMessage message) {});
}
#override
Widget build(BuildContext context) {
return Scaffold(
extendBody: true,
backgroundColor: Colors.white,
appBar: null,
body: ListView(
children: [
notific != null
? Card(
margin: EdgeInsets.all(10),
elevation: 4,
child: ListTile(
title: Text(
title ?? '',
),
subtitle: Text(
body ?? '',
),
),
)
: Container(
child: Text("U don't have new notifcs."),
),
],
),
);
}
}