Cannot get uid in facebook application

[chonghua]

I create facebook application names \[code\]http://apps.facebook.com/mysapp/\[/code\] and i need to implement facebook library to get uid from user.my code is\[code\]require_once('inc/_facebook_library.php'); $facebook = new Facebook(array( 'appId' => 'APPID', 'secret' => 'SECRET', 'cookie' => true, )); $session = $facebook->getSession(); $me = null; // Session based API call. if ($session) { try { $uid = $facebook->getUser(); $me = $facebook->api('/me'); echo $uid; } catch (FacebookApiException $e) { echo 'sdsds'; error_log($e); } }\[/code\]I try to echo $uid; but it doesn't show. how i fix it. thanks!!