CODEWITHSUNDEEP
flutterpush-notificationfirebase-cloud-messaging
chichi
chichi

Reputation: 3292

Flutter: FCM Unhandled Exception: Null check operator used on a null value

E/flutter (26872): [ERROR:flutter/lib/ui/ui_dart_state.cc(199)] Unhandled Exception: Null check operator used on a null value E/flutter (26872): #0
MethodChannelFirebaseMessaging.registerBackgroundMessageHandler (package:firebase_messaging_platform_interface/src/method_channel/method_channel_messaging.dart:173:53) E/flutter (26872): #1
FirebaseMessagingPlatform.onBackgroundMessage= (package:firebase_messaging_platform_interface/src/platform_interface/platform_interface_messaging.dart:108:16)

// Background Messaging Set Up
    Future<void> _firebaseMessagingBackgroundHandler(
        RemoteMessage message) async {
      print('background message');
    }

    FirebaseMessaging.onBackgroundMessage(_firebaseMessagingBackgroundHandler);
    runApp(....)

I am getting an error for this code on Android system. Everything works except when the app is terminated.

What works on Android:

What does not work on Android:

What works on iOS:

What does not work on iOS:

I have no clue why I am getting that null value error on Android system and how can I fix this issue? Also, is it true that I can not receive the Data only push notification on iOS when the app is terminated?

Upvotes: 41

Views: 19406

Answers (4)

Aya Alsaity
Aya Alsaity

Reputation: 1

Future<void> backgroundNotification() async {
// await FirebaseMessaging.instance.setDeliveryMetricsExportToBigQuery(true);
FirebaseMessaging.onMessage.listen((RemoteMessage message) {
  if (kDebugMode) {
    print("message ===> $message");
    print("message ===> ${message.sentTime}");
    print("message ===> ${message.notification?.title}");
    print("message ===> ${message.notification?.body}");
  }
  if (message.notification!.title!.isNotEmpty &&
      message.notification!.body!.isNotEmpty) {
    // Can use package:flutter_local_notifications for show notifications in app.
  }
});
}

Upvotes: 0

M.Taha Basiri
M.Taha Basiri

Reputation: 651

In my case, doing what docs said was not enough. So I realized that I should add WidgetsFlutterBinding.ensureInitialized() before everything in main function like this:

void main() {
  WidgetsFlutterBinding.ensureInitialized();
  FirebaseMessaging.onBackgroundMessage(_handleMessage);
  runApp(const Homino());
}

Upvotes: 6

Rafsan Uddin Beg Rizan
Rafsan Uddin Beg Rizan

Reputation: 2287

_firebaseMessagingBackgroundHandler function should be outside of the main function.

Future<void> _firebaseMessagingBackgroundHandler(RemoteMessage message) async {
  await Firebase.initializeApp();
}


Future<void> main() async {

  FirebaseMessaging.onBackgroundMessage(_firebaseMessagingBackgroundHandler);


  runApp(
    ...
  );
}

Upvotes: 29

Paras Khanagwal
Paras Khanagwal

Reputation: 1673

I had the same error as like you, on the same line. I checked out docs and it says 2 things about background message handler.

  1. It must not be an anonymous function.
  2. It must be a top-level function (e.g. not a class method which requires initialization).

In my case it was not a top-level function, it was declared inside a class. When you move your handler out of any class or function, so that it is a top-level function and doesn't require any class or method initialisation then the error will be gone.

Upvotes: 78

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