1. protected
void registerSignalServiceExtension({@required String name, @required VoidCallback callback })

Registers a service extension method with the given name (full name "ext.flutter.name"), which takes no arguments and returns no value.

Calls the callback callback when the service extension is called.

Source 

@protected
void registerSignalServiceExtension({
  @required String name,
  @required VoidCallback callback
}) {
  assert(name != null);
  assert(callback != null);
  registerServiceExtension(
    name: name,
    callback: (Map<String, String> parameters) async {
      callback();
      return <String, dynamic>{};
    }
  );
}