public SubscriberViewModel(Subscriber subscriber, SubscriberService subscriberService)
        {
            if (subscriber == null)
                throw new ArgumentNullException("subscriber");

            if (subscriberService == null)
                throw new ArgumentNullException("subscriberService");

            _subscriber = subscriber;
            _subscriberService = subscriberService;
        }
        public SubscriberListViewModel(SubscriberService service)
        {
            DisplayName = Resources.SubscriberList_DisplayName;

            if (service == null) {
                throw new ArgumentNullException("Invalid service");
            }

            _subscriberService = service;

            _subscriberService.SubscriberAdded += this.OnSubscriberAddedToRepository;
            _subscriberService.SubscriberDeleted += this.OnSubscriberDeletedFromRepository;

            LoadSubscribers();
        }