void OnSubscriberDeletedFromRepository(object sender, SubscriberChangedEventArgs e)
 {
     SubscriberPane = new SubscriberViewModel(Subscriber.CreateNewSubscriber(), _subscriberService);
     for (int i = 0; i < this.AllSubscribers.Count; i++) {
         if (this.AllSubscribers[i].Subscriber == e.Subscriber) {
             this.AllSubscribers.RemoveAt(i);
         }
     }
 }
 void OnSubscriberAddedToRepository(object sender, SubscriberChangedEventArgs e)
 {
     var viewModel = new SubscriberViewModel(e.Subscriber, _subscriberService);
     this.AllSubscribers.Add(viewModel);
 }