Problem in member area session validation

[eluser]Unknown[/eluser]
Hello , i am new in CI and trying to make a member only area , everything is ok , but i have a problem making the member area check if the user logged in or not!!

when user logging he should redirect to http://localhost/index.php/admin/members
and its done , but always i got message : You don't have permission to access this page.!! please Login!!! even the provided username and password is correct.

My CI version : 2.1

members Controller

Code:

class members extends CI_Controller{
  
    function __construct() {
        parent::__construct();
  
  $this->is_logged_in();
}

  function index(){
  
   $this->load->view('admin/members');
  }
  
function is_logged_in()
{
  $is_logged_in = $this->session->userdata('is_logged_in');
  if(!isset($is_logged_in) || $is_logged_in != true)
  {
     echo 'You don\'t have permission to access this page.!! please <a href="../admin/login">Login</a>';
     die();
    }
  
  }
}

Login Controller

Code:

class login extends CI_Controller {
    
    function index()
    {
    $data['main_content'] = 'admin/login_form';
    $this->load->view('admin/includes/template', $data);    
    }
    
    function validate_credentials()
    {
        $this->load->model('admin/user_login_model');
  $query = $this->user_login_model->validate();
  
        if($query)//if the login detalis right then
        {
         $data = array(
   'username' =>$this->input->post('username'),
   'is_loggedin' => true
   );
  
   $this->session->set_userdata($data);
   redirect('admin/members');
        }
  else {
   $this->index();
  }
    }

function forgot(){
  
   $data['main_content'] = 'admin/forgot_form';
   $this->load->view('admin/includes/template', $data);  
}  
}
?>

so how i can fix that ?
Thanks