无法在codeigniter中的第二个函数中获取会话内容

I have issue with session in codeigniter.

I have used session library. So I have stored username in session. In Login function I am able to store and retrieve session data. but in second function which is GetUserName in this function I am not able to retrieve userName from the session.

Does anyone have any ideas what I am doing wrong here?

<?php
defined('BASEPATH') OR exit('No direct script access allowed');
header('Access-Control-Allow-Origin: *');
class LoginController extends CI_Controller {

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

        $this->load->helper('url');
        $this->load->library('session');
    }

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

    }

    public function Login() {   
        $UserName=$this->input->post('UserName');
        $Password=$this->input->post('Password');
        $this->session->set_userdata('UserName',$UserName);
        echo $Name=$this->session->userdata('UserName');
    }

    public function Log() {
        $this->load->view('welcome_message');
    }

    public function GetUserName() {
        echo $U_Name=$this->session->userdata('UserName');
    }
}

try the following:

to set the session use this:

$UserName=$this->input->post('UserName');
$newdata = array('username'  => $UserName);
$this->session->set_userdata('login_user_data',$newdata);

to retrieve values from session use:

$this->session->userdata['login_user_data']['username'];