private void AddPatient(object sender, RoutedEventArgs e) { if (!string.IsNullOrEmpty(txtName.Text.Trim()) && !string.IsNullOrEmpty(txtSurname.Text.Trim())) { patientRegistry.Add(ModelCreator.CreatePatient(txtName.Text, txtSurname.Text)); this.Close(); } else { MessageBox.Show("Enter data", "Error", MessageBoxButton.OK, MessageBoxImage.Error); return; } }