protected override void OnAddClickedCommand()
 {
     IsDelButtonEnabled                = false;
     EditViewModelInstance             = new RegistrationEditViewModel(Repository, RoomsRepository, GuestsRepository, DiscountsRepository, GuestsDiscountsRepository);
     EditViewModelInstance.CloseEvent += () =>
     {
         EditViewModelInstance = null;
         IsDelButtonEnabled    = true;
     };
 }
 protected override void OnEditClickedCommand()
 {
     //check!
     EditViewModelInstance = new RegistrationEditViewModel(Repository, RoomsRepository, GuestsRepository, DiscountsRepository, GuestsDiscountsRepository);
 }