addListener method Null safety

void addListener(
  1. void listener(
      )
    )

    Listens to contact database changes.

    Because of limitations both on iOS and on Android (see https://www.grokkingandroid.com/use-contentobserver-to-listen-to-changes/) it's not possible to tell which kind of change happened and on which contacts. It only notifies that something changed in the contacts database.

    Implementation

    static void addListener(void Function() listener) {
      if (_eventSubscription != null) {
        _eventSubscription!.cancel();
      }
      _eventSubscribers.add(listener);
      final runAllListeners = (event) => _eventSubscribers.forEach((f) => f());
      _eventSubscription =
          _eventChannel.receiveBroadcastStream().listen(runAllListeners);
    }