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[Flutter/dart] null check operator used on a null value messaging


Overview

A title error has occurred at FirebaseMessaging.onBackgroundMessage().



Cause and Solution

The delegate passed to the argument of the above method must be a top-level function. In my case, I was passing an instance method, so the error occurred.

The error disappeared when the method passed was a top-level function.


@main.dart

void main() async{
  //・・・
  FirebaseMessaging.onBackgroundMessage(onBackGround);
}

Future<void> onBackGround(RemoteMessage message)async{
  //・・・
}


Reference

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