cakephp - 检查会话是否已设置

I'm new to cakephp and following this tutorial. http://book.cakephp.org/2.0/en/tutorials-and-examples/blog-auth-example/auth.html

I have created the blog and the user authentication system. I'm trying to display a link to sign in(if the user isn't signed in) or display a link to sign out (if the user is signed in).

So, essentially I'm checking to see if the session is set. If it is, display a link to log out. If the session isn't set, display a link to sign in.

This is in my file index.ctp located in View/Posts/index.ctp. The file containing the login and logout functions are located in Controller/UsersController.php.

<?php 
if($this->Auth->User('id')){ 
    echo $this->Html->link('Log Out', array('controller' => 'users','action' => 'logout'));
}

if(!($this->Auth->User('id'))){ 
    echo $this->Html->link('Log In', array('controller' => 'users','action' => 'login'));
}
?> 

I'm getting the following error: Fatal error: Call to a member function User() on a non-object. I know this means the object isn't defined, but I'm not sure how to reference it to another controller.

Thanks for any help.

Auth is a component and thus is not available in your view, those are called helpers.

To access Session var within a view you would do

$this->Session->check('Auth.User');