private String getLabel(final int idx, final T value) {
        if (value == null) {
            return "-";
        }
        if (labelMapper != null) {
            return labelMapper.call(idx, value);
        }
        return String.valueOf(value);
    }
View displays and maintains a slider where user can select single or range of items from a sorted item list.
main/src/main/java/cgeo/geocaching/ui/ItemRangeSlider.java