如何在fields_list中添加动态字段？

Question

我在fields_list中有几个静态字段，但我希望它们动态添加更多字段，其中title是Prestashop中我的字段label数据库的结果。

public function renderResultsList()
    {

    $this->_select = '
                    ro.*, rol.*,ruo.*, cus.`id_customer`, cus.`firstname`, cus.`lastname`, cus.`email`, cus.`date_add`' ;
                $this->_join = '
                    LEFT JOIN `' . _DB_PREFIX_ . 'registform_options` ro ON (ro.`id_reg` = a.`id_reg`)
                    LEFT JOIN `' . _DB_PREFIX_ . 'registform_options_lang` rol ON (rol.`id_option` = ro.`id_option` AND rol.`id_lang` = ' . (int) $this->context->language->id . ')
                    LEFT JOIN `' . _DB_PREFIX_ . 'registform_user_options` ruo ON (ruo.`id_reg` = a.`id_reg`)
                    LEFT JOIN `' . _DB_PREFIX_ . 'customer` cus ON (ruo.`id_user` = cus.`id_customer`)';

     $this->fields_list = array(
                    'id_customer' => array(
                        'title' => $this->l('ID'),
                        'width' => 'auto',
                        'align' => 'center'
                    ),
                    'firstname' => array(
                        'title' => $this->l('First name'),
                        'width' => 'auto',
                        'align' => 'center'          
                    ),
                    'lastname' => array(
                        'title' => $this->l('Last name'),
                        'width' => 'auto',
                        'align' => 'center'
                    )

                );

                $ind = 0;
                foreach($this->_result as $r){
                    $this->fields_list[$ind]['label'][$ind] = $r['label'];
                    $ind++;

                }
    $this->tpl_list_vars['title'] = $this->l('Results');

                return parent::renderList();
            }