public void EditCat(Cat cat)
 {
     if (cat != null)
     {
         CatViewModel catViewModel = new CatViewModel(CatsModel, cat);
         ((App)Application.Current).WindowService.ShowDialog(catViewModel);
     }
 }
        public void AddCat()
        {
            CatViewModel catViewModel = new CatViewModel(CatsModel);

            ((App)Application.Current).WindowService.ShowDialog(catViewModel);
        }