@Override
    protected void onRestoreInstanceState(@NonNull final Bundle savedInstanceState) {
        super.onRestoreInstanceState(savedInstanceState);
        if (savedInstanceState.getString(STATE_CURRENT_FILTER) != null) {
            fillViewFromFilter(savedInstanceState.getString(STATE_CURRENT_FILTER), savedInstanceState.getBoolean(STATE_ADVANCED_VIEW));
        }
        filterContext = (GeocacheFilterContext) savedInstanceState.getSerializable(STATE_FILTER_CONTEXT);
        if (filterContext == null) {
            filterContext = new GeocacheFilterContext(TRANSIENT);
        }
        originalFilterConfig = savedInstanceState.getString(STATE_ORIGINAL_FILTER_CONFIG);
    }
Show a filter selection using an {@code ExpandableListView}.
main/src/main/java/cgeo/geocaching/filters/gui/GeocacheFilterActivity.java