public static Set<Integer> getLastSelectedLists() {
        final Set<Integer> lastSelectedLists = new HashSet<>();
        for (final String lastSelectedListString : getStringList(R.string.pref_last_selected_lists, StringUtils.EMPTY)) {
            try {
                lastSelectedLists.add(Integer.valueOf(lastSelectedListString));
            } catch (final NumberFormatException ignored) {
            }
        }
        return lastSelectedLists;
    }
remember the last displayed cache list
main/src/main/java/cgeo/geocaching/settings/Settings.java