public function get_filters() {
        $filterkeys = [
            ASSIGN_FILTER_SUBMITTED,
            ASSIGN_FILTER_NOT_SUBMITTED,
            ASSIGN_FILTER_REQUIRE_GRADING,
            ASSIGN_FILTER_GRANTED_EXTENSION
        ];

        $current = get_user_preferences('assign_filter', '');

        $filters = [];
        // First is always "no filter" option.
        array_push($filters, [
            'key' => 'none',
            'name' => get_string('filternone', 'assign'),
            'active' => ($current == '')
        ]);

        foreach ($filterkeys as $key) {
            array_push($filters, [
                'key' => $key,
                'name' => get_string('filter' . $key, 'assign'),
                'active' => ($current == $key)
            ]);
        }
        return $filters;
    }