register a callbackdispatcher

simple_callback_dispatcher_registration.dart

void callbackDispatcher() {
  WidgetsFlutterBinding.ensureInitialized();
  print("Our background job ran!");
}

void main() {
  static const MethodChannel _channel = const MethodChannel("channel-name");

  Future<void> initialize(final Function callbackDispatcher) async {
    final callback = PluginUtilities.getCallbackHandle(callbackDispatcher);
    await _channel.invokeMethod('initialize', callback.toRawHandle());
  }
}