public TextSpinner<T> setCheckedMapper(@Nullable final Func1<T, Boolean> setCheckedMapper) {
        this.setCheckedMapper = setCheckedMapper;
        return this;
    }
if spinner is be represented as a {@link Checkable} textview (e.g. a {@link android.widget.ToggleButton},
set whether checkable is turned on or off dependent on displayed value
main/src/main/java/cgeo/geocaching/ui/TextSpinner.java