In my app, I have a default push notification topic "DEFAULT" which is subscribed by all the user. Whenever a new topic is created, I send a push notification over "DEFAULT" topic with a data/payload property containing the new notification topic name, to all the users. The app accepts the notification and takes out the new topic from the payload. If the new topic is valid for the user then it subscribes to it, otherwise ignores it. Below is the code that is working properly only when the app is in foreground state,
static void _handleForegroundMessages() async { FirebaseMessaging.onMessage.listen((RemoteMessage message) { String? topicChannel = message.data['topic']; if (topicChannel != null && topicChannel == PredefinedNotificationTopic.topicCreated.name) { String newTopic = message.data['newTopicToSubscribe']; FCMHelper.addToUserTopicList(newTopic); } _showLocalNotification(message); })};However, the similar code for background/terminated state is throwing exception as below
E/flutter (24845): [ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: [core/no-app] No Firebase App '[DEFAULT]' has been created - call Firebase.initializeApp()E/flutter (24845): #0 MethodChannelFirebase.app (package:firebase_core_platform_interface/src/method_channel/method_channel_firebase.dart:193:5)E/flutter (24845): #1 Firebase.app (package:firebase_core/src/firebase.dart:56:41)E/flutter (24845): #2 FirebaseMessaging.instance (package:firebase_messaging/src/messaging.dart:32:47)E/flutter (24845): #3 FCMService.subscribeToTopics (package:fourdrinier/service/fcm_service.dart:52:25)E/flutter (24845): #4 FCMHelper.addToUserTopicList (package:fourdrinier/service/fcm_helper.dart:45:18)E/flutter (24845): <asynchronous suspension>Is it possible to achieve the same? or is there any work around?
Here is my background handler that I am calling using FirebaseMessaging.onBackgroundMessage(FCMService.backgroundHandler);
static Future<void> backgroundHandler(RemoteMessage message) async { String? topicChannel = message.data['topic']; debugPrint("Background notification with $topicChannel"); if (topicChannel != null && topicChannel == PredefinedNotificationTopic.topicCreated.name) { String newTopic = message.data['newTopicToSubscribe']; FCMHelper.addToUserTopicList(newTopic); } }