public TextSpinner<T> setTextDisplayMapper(@Nullable final Func1<T, TextParam> textDisplayMapper) {
        this.textDisplayMapper = textDisplayMapper;
        repaintDisplay();
        return this;
    }
if spinner is be represented as a textview, set how currently selected value is displayed
If not set, then mapper set with {@link #setDisplayMapperPure(Func1)} is used
main/src/main/java/cgeo/geocaching/ui/TextSpinner.java