public function test(){
        $data = ORM::factory('testdata')->find_all();
        Table::factory()
            ->set_body_data($data)
            ->set_row_titles('id')
            ->set_column_titles(Table::AUTO)
            ->set_callback('format_row', 'row')
            ->render(true);
            $this->template->title = '';
            $this->template->payment_content = '';
    }
    function format_row($row, $index){
        if ($index % 2 == 0) return new Tr('', 'zebra');
    }
// getting an error : callback function format_row does not exist!, both methods declared in a controller class (Payment_Controller)
how do I do callbacks in MVC?