@Override
    public void onSaveInstanceState(@NonNull final Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putString(STATE_CURRENT_FILTER, getFilterFromView().toConfig());
        outState.putBoolean(STATE_ADVANCED_VIEW, isAdvancedView());
        outState.putParcelable(STATE_FILTER_CONTEXT, filterContext);
        outState.putString(STATE_ORIGINAL_FILTER_CONFIG, originalFilterConfig);
    }
Show a filter selection using an {@code ExpandableListView}.
main/src/main/java/cgeo/geocaching/filters/gui/GeocacheFilterActivity.java