Extend Form_Validation

I try but not work.
I am using Codeigniter 3.0.6 (last version)

PHP Code:

<?php if (!defined('BASEPATH')) exit('No direct script access allowed');

class MY_Form_validation extends CI_Form_validation
{
    public function __construct()
    {        parent::__construct();    }

    public function url($str)
    {
        $pattern = "|^http(s)?://[a-z0-9-]+(.[a-z0-9-]+)*(:[0-9]+)?(/.*)?$|i";
        if (!preg_match($pattern, $str))
        {
            $this->form_validation->set_message('url', 'The URL you entered is not correctly formatted.');
            return FALSE;
        } 
        else
        {  return TRUE;    }
    }
} 


Controller example code:

PHP Code:

<?php if (!defined('BASEPATH')) exit('No direct script access allowed');

class Example_c extends CI_Controller
{
    public function __construct()
    {
        parent::__construct();
        $this->load->library('form_validation');
    }

    public function index()
    {
        //echo 'Example';
    }
} 


I believe that the controller does not read extensive library, but only the message from the language file