A background message could not be handled in dart as no onbackgroundmessage handler has been registered.

In Dart, the background message cannot be handled directly because no onBackgroundMessage handler has been registered.

When using platforms like Flutter, you can handle background messages by using a library called firebase_messaging. This library provides a way to handle both foreground and background messages in Dart.

Here’s an example of how you can handle background messages using the firebase_messaging library:

import 'package:firebase_messaging/firebase_messaging.dart';

FirebaseMessaging _firebaseMessaging = FirebaseMessaging.instance;

// Registering the background message handler
Future<void> configureBackgroundMessageHandler() async {
  FirebaseMessaging.onBackgroundMessage(_backgroundMessageHandler);
}

// The background message handler function
Future<void> _backgroundMessageHandler(RemoteMessage message) async {
  // Handle the background message here
  print('Background message received: ${message.data}');
  // Perform tasks or show notifications based on the message

  // Don't forget to call finish() to let the system know that the background message handling is done
  FirebaseMessaging.instance.setAutoInitEnabled(true);
}

void main() async {
  // Call the method to register the background message handler
  await configureBackgroundMessageHandler();

  // Rest of your app code comes here
}
  

In the example above, the configureBackgroundMessageHandler() method is responsible for registering the _backgroundMessageHandler() as the background message handler. This method is called in the main() function to ensure that the background message handler is set up before the app starts.

The _backgroundMessageHandler() function is where you handle the background message received. You can perform tasks or show notifications based on the message content. After handling the background message, don’t forget to call finish() to let the system know that the background message handling is done.

This is just a basic example, and you can customize the background message handling based on your specific requirements. Make sure to check the documentation of the firebase_messaging library for more details and advanced usage.