Get error while I'm creating a library on Codeigniter

I created this library:

class Header 
{

    function __construct()
    {
        $this->user();
    }

    function user()
    {
        开发者_JAVA技巧$my_user = $this->session->userdata('my_user'); // True or False

        if($my_user)
        {
            echo 'user!';
        }
    }

}

/* End of file Header.php */

I call it in any controller:

public function __construct()
    {
        parent::__construct();
        $this->load->library('Header');
    }

The error:

Fatal error: Call to a member function userdata() on a non-object in ** on line 11

I don't know what is the problem, I'm sure that the library session is called (I call it from autoload)... what can I do? When this library code is in any controller it works great, the problem is anywhere with custom library.

That won't work in a library, see the documentation.

$CI =& get_instance();
$CI->load->library('session');

$my_user = $CI->session->userdata('my_user');

The issue you're running into is that in a library, the CI object (this) isn't loaded, you need to get it.

So try this (a reference to the CI object is stored in the $CI variable):

class Header 
{
    private $CI;
    function __construct()
    {
        $this->user();
        if (!isset($this->CI))
    $this->CI =& get_instance();
    }

    function user()
    {
        $my_user = $this->CI->session->userdata('my_user'); // True or False

        if($my_user)
        {
            echo 'user!';
        }
    }

}

In the constructor, you get a reference to the CI object, and store that in the $CI variable, then you use that when you want to access its methods etc.