private void ShowCat_Click(object sender, RoutedEventArgs e) { if (catsList.SelectedItem != null) { string name = catsList.SelectedItem.ToString(); CatParameters selectedCat = _catsList.Find(selCat => selCat.catName == name); var newWPF = new CatDetails(selectedCat); newWPF.CatDetail(); newWPF.Show(); } else { MessageBox.Show("Choose a cat!", "ERROR", MessageBoxButton.OK, MessageBoxImage.Error); } }