Flutter: How to subscribeToTopic for Firebase (FCM) registration token in Flutter - firebase

Question

I want to subscribeToTopic for Firebase push notification in flutter , I can subscribe to any topic but my purpose to subscribeToTopic against token , here it is the code below,
FirebaseMessaging _messaging;
Firebase.initializeApp().then((fbr) {
_messaging = FirebaseMessaging.instance;
_messaging.getToken().then((token) async{
_messaging.subscribeToTopic(token).then((value) => null);
_messaging.subscribeToTopic(userID).then((value) => null);
_messaging.subscribeToTopic(userTypeId).then((value) => null);
}
}
But I am getting error
Failed assertion: line 307 pos 10: 'isValidTopic': is not true.
log attached below:
I/flutter ( 9352): Token: dhCABsvbQ8udQJha8VOxNy:APA91bEGcpS6-QMn-c236ITNbDtxEs3MD1Q-nquedMLzZv4XWPdGUWt-Zw-OQ6YBY383IJGZXxKXNMRJd8SKLeOO7agx4dcym6VoEhPTrbYr20NoscZHTZoPCf5mqbfiTHCS5q2WlXqw
I/flutter ( 9352): User granted permission
I/flutter ( 9352): Token: dhCABsvbQ8udQJha8VOxNy:APA91bEGcpS6-QMn-c236ITNbDtxEs3MD1Q-nquedMLzZv4XWPdGUWt-Zw-OQ6YBY383IJGZXxKXNMRJd8SKLeOO7agx4dcym6VoEhPTrbYr20NoscZHTZoPCf5mqbfiTHCS5q2WlXqw
E/flutter ( 9352): [ERROR:flutter/lib/ui/ui_dart_state.cc(186)] Unhandled Exception: 'package:firebase_messaging/src/messaging.dart': Failed assertion: line 307 pos 10: 'isValidTopic': is not true.
E/flutter ( 9352): #0 _AssertionError._doThrowNew (dart:core-patch/errors_patch.dart:46:39)
E/flutter ( 9352): #1 _AssertionError._throwNew (dart:core-patch/errors_patch.dart:36:5)
E/flutter ( 9352): #2 _assertTopicName (package:firebase_messaging/src/messaging.dart:307:10)
E/flutter ( 9352): #3 FirebaseMessaging.subscribeToTopic (package:firebase_messaging/src/messaging.dart:294:5)
E/flutter ( 9352): #4 _HomePageState.registerNotification.<anonymous closure> (package:notify/main.dart:89:20)
E/flutter ( 9352): #5 _rootRunUnary (dart:async/zone.dart:1362:47)
E/flutter ( 9352): #6 _CustomZone.runUnary (dart:async/zone.dart:1265:19)
E/flutter ( 9352): #7 _FutureListener.handleValue (dart:async/future_impl.dart:152:18)
E/flutter ( 9352): #8 Future._propagateToListeners.handleValueCallback (dart:async/future_impl.dart:704:45)
E/flutter ( 9352): #9 Future._propagateToListeners (dart:async/future_impl.dart:733:32)
E/flutter ( 9352): #10 Future._completeWithValue (dart:async/future_impl.dart:539:5)
E/flutter ( 9352): #11 _completeOnAsyncReturn (dart:async-patch/async_patch.dart:254:13)
E/flutter ( 9352): #12 MethodChannelFirebaseMessaging.getToken (package:firebase_messaging_platform_interface/src/method_channel/method_channel_messaging.dart)
E/flutter ( 9352): <asynchronous suspension>

Answer 1

The error is coming up because the token id you're passing as the topic name is not an acceptable topic name.
Here is the check that the token fails:
// https://github.com/FirebaseExtended/flutterfire/blob/master/packages/firebase_messaging/firebase_messaging/lib/src/messaging.dart
void _assertTopicName(String topic) {
bool isValidTopic = RegExp(r'^[a-zA-Z0-9-_.~%]{1,900}$').hasMatch(topic);
assert(isValidTopic);
}
Source
Use a valid string and the code should work fine.