懂cakephp的帮忙看一下这段cakephp的代码,为什么AuthComponent:user('id')取不到值,该怎么解决

function login(){
        if(empty($this->request->data['User']['username']) or empty($this->request->data['User']['password'])){
            $this->Session->setFlash('Please intyped a valied account!');
        }elseif ($this->Auth->login($this->request->data['User'])) {
            $this->User->id= AuthComponent::user('id');
            $this->redirect("/users/index");    
        }
        else{                
                $this->redirect("/users/logout");    
            }    
        }