public GroupingOptions<G> setGroupDisplayViewMapper(final Func5<G, ItemGroup<T, G>, Context, View, ViewGroup, View> groupDisplayViewMapper) {
            if (groupDisplayViewMapper != null) {
                this.groupDisplayViewMapper = groupDisplayViewMapper;
                triggerChange(ChangeType.COMPLETE);
            }
            return this;
        }
Sets a mapper providing the text visualization for a group item
main/src/main/java/cgeo/geocaching/ui/SimpleItemListModel.java