@Override
  public View getView(int position, View convertView, ViewGroup parent) {
    View rowView = convertView;

    Customer currentItem = getItem(position);

    // reuse views
    if (rowView == null) {
      LayoutInflater inflater = context.getLayoutInflater();
      rowView = inflater.inflate(R.layout.customer_list_item, null);
      rowView.setTag(currentItem.getDevice());
    }

    // fill data

    ((TextView) rowView.findViewById(R.id.customerName)).setText(currentItem.getName());
    ((TextView) rowView.findViewById(R.id.customerLastSeenValue))
        .setText(currentItem.getLastSeenString());

    if (currentItem.getLoyality() > 0) {
      ((TextView) rowView.findViewById(R.id.customerLoyality))
          .setText(String.valueOf(currentItem.getLoyality()));
      ((TextView) rowView.findViewById(R.id.customerWorth))
          .setText((currentItem.getLoyality() * 3) + "€");
    } else {
      ((TextView) rowView.findViewById(R.id.customerLoyality)).setVisibility(View.GONE);
      ((TextView) rowView.findViewById(R.id.customerWorth)).setVisibility(View.GONE);
    }

    // load image
    ImageView itemImage = (ImageView) rowView.findViewById(R.id.customerPicture);
    itemImage.setImageDrawable(currentItem.getPicture());

    return rowView;
  }
  private void updateValues() {
    customer = app.getCustomerByDevice(customerDevice);

    customerName.setText(customer.getName());
    customerImage.setImageDrawable(customer.getPicture());

    seekBar.setProgress(customer.getLoyality());
    loyalityValue.setText(customer.getLoyality() + " / 10");

    if (customer.getLoyality() == 10) {
      offerPromoButton.setEnabled(true);
    } else {
      offerPromoButton.setEnabled(false);
    }
  }