code: public void setValues(List<T> values, boolean fireEvents) {
          String[] stringValues = new String[values.size()];
          for (int i = 0; i < values.size(); i++) {
              stringValues[i] = keyFactory.generateKey(values.get(i));
          }
          suppressChangeEvent = !fireEvents;
          $(listbox.getElement()).val(stringValues).trigger("change", selectedIndex);
          suppressChangeEvent = false;
      }
docs: Set directly all the values that will be stored into
  combobox and build options into it.