public function load_choices() {
        if (is_array($this->choices)) {
            return true;
        }
        $this->choices = array();

        if ($plugins = core_component::get_plugin_list('gradeexport')) {
            foreach($plugins as $plugin => $unused) {
                $this->choices[$plugin] = get_string('pluginname', 'gradeexport_'.$plugin);
            }
        }
        return true;
    }