private void DeleteUserButton_Click(object sender, RoutedEventArgs e)
        {
            var selectedItem = this.lvVolunteers.SelectedItem;

            if (selectedItem != null)
            {
                VolunteerEntity volunteer = selectedItem as VolunteerEntity;

                VolunteerService service = new VolunteerService();
                if (MessageBox.Show("Sei sicuro di voler eliminare \"" + volunteer.Name + " " + volunteer.Surname + " \" ?", "Elimina Volontario", MessageBoxButton.YesNo) == MessageBoxResult.Yes)
                {
                    if (service.Delete(volunteer) == 0)
                    {
                        MessageBox.Show("cancellato!");
                        this.RefreshData();
                    }
                    else
                    {
                        MessageBox.Show("NON cancellato!");
                    }
                }
                else
                {
                    MessageBox.Show("NON cancellato!");
                }
            }
        }