重定向到登录页面 - Codeigniter

Question

I want to check the session; if it exits it goes to my web site, otherwise redirecting to "login" page; here is my controller:

function __construct() {
    parent::__construct();
    $this->is_logged_in();
}

public function index($failed=FALSE) {
    $data['main_content'] = 'login_view';
    $data['failed_validation'] = $failed;
    $this->load->view('includes/template', $data);
}

public function is_logged_in() {
    if ($this->session->userdata('f_name') != null) {
        return;
    } else {
        $this->index();
       //die()// This one does not help either
    }
}

public function display_site() {
    $data['main_content'] = 'site_view';
    $this->load->view('includes/template', $data);
}

This is the version after suggestion(but still the same problem!):

Controller:

function __construct() {
    parent::__construct();
    $this->load->model('user_model');
    if ($this->user_model->is_logged_in() == FALSE) {
        $this->index();
    }
}

public function index($failed=FALSE) {
    $data['main_content'] = 'login_view';
    $data['failed_validation'] = $failed;
    $this->load->view('includes/template', $data);
}

public function login() {
    $data['main_content'] = 'login_view';
    $data['failed_validation'] = FALSE;
    $this->load->view('includes/template', $data);
}

Model:

  public function is_logged_in()
    {
         return ($this->session->userdata('is_logged_in') );
    }

Thats fine but when the user goes to logs in page, it shows both login page and my website main page! In other hand even if I die in (see the comment in my code) it does not help, it gives me a blank page!

Thanks

Answer 1

Login Controller:

class Login extends CI_Controller {

    public function __construct() {
        parent::__construct();
    }

    public function index() {
        $this->load->view('includes/login');
    }
}

Main Controller:

class Main extends CI_Controller {
    public function __construct() {
        parent::__construct();      
            $this->load->model('user_model');
            if (!$this->user_model->is_logged_in()) {
               redirect(base_url().'login', 'location', 301);
            }   
    }

    public function index() {
        $this->load->view('includes/main');
    }
}