使用PHPSDK登录Facebook

当我登录时，一切都很好，我得到了用户id和姓名，但是当我点击注销按钮时，它只是将我从facebook注销，没有其他任何事情发生。按钮不想更改为登录。为什么？它只是忽略了语句的其他部分

public function fblogin() {

            require_once '../application/libraries/facebook.php';

            //Create our Application instance
            $facebook = new Facebook(array(
                'appId' => '**********', // Facebook App ID
                'secret' => '*******************', // Facebook App Secret

            ));

            //Get User ID
            $user = $facebook->getUser();

            if (isset($user)) {
                try {

                  $me = $facebook->api("/me"); 

                } catch (FacebookApiException $e) {
                    $user = null;
                    echo $e-> getMessage(); 
                }

                if ($me) {

                    $logoutUrl = $facebook->getLogoutUrl();
                    echo $me["id"];
                    echo $me["name"];
                    echo ("<a href='$logoutUrl'>Logout</a>");

                }

            }

            else {

                $loginUrl = $facebook->getLoginUrl();
                echo ("<a href='$loginUrl'>Login</a>");
            }


        }

---

如果你在这个分数的末尾加上else

public function fblogin() {

            require_once '../application/libraries/facebook.php';

            //Create our Application instance
            $facebook = new Facebook(array(
                'appId' => '**********', // Facebook App ID
                'secret' => '*******************', // Facebook App Secret

            ));

            //Get User ID
            $user = $facebook->getUser();

            if (isset($user)) {
                try {

                  $me = $facebook->api("/me"); 

                } catch (FacebookApiException $e) {
                    $user = null;
                    echo $e-> getMessage(); 
                }

                if ($me) {

                    $logoutUrl = $facebook->getLogoutUrl();
                    echo $me["id"];
                    echo $me["name"];
                    echo ("<a href='$logoutUrl'>Logout</a>");

                }

            }

            else {

                $loginUrl = $facebook->getLoginUrl();
                echo ("<a href='$loginUrl'>Login</a>");
            }


        }

if ($me) {

                $logoutUrl = $facebook->getLogoutUrl();
                echo $me["id"];
                echo $me["name"];
                echo ("<a href='$logoutUrl'>Logout</a>");

            } else {

            $loginUrl = $facebook->getLoginUrl();
            echo ("<a href='$loginUrl'>Login</a>");
        }

---

检查此代码在注销$user=$facebook->getUser；后返回的内容；，也许$user仍然验证为true。。。