public MainViewModel(INavigation navigation)
 {
     _navigation = navigation;
     _database = new Database();
     Contacts = new ObservableCollection<Contact>(_database.SearchContacts(""));
     AddCommand = new Command(ShowAddWindow);
 }
 public ContactViewModel(INavigation navigation, Contact contact)
 {
     _navigation = navigation;
     _contact = contact;
     SaveCommand = new Command(OnSave);
 }