private void AddButton_Click(object sender, RoutedEventArgs e) { if (StationsList.SelectedItem == null) { MessageBox.Show("Any station was not chosen!"); return; } if (!_repo.IsFavouriteStationUnique(_user, (Station)StationsList.SelectedItem)) { MessageBox.Show("Such station is already in your favourites list!"); return; } _repo.AddFavourite(_user, (Station)StationsList.SelectedItem, DescriptionTexBox.Text); DialogResult = true; }