要获取用户的Facebook ID，您需要进行Graph API调用.要进行该API调用，首先需要通过调用代码的这一部分来请求用户许可:

To get the user's Facebook ID, you need to make Graph API call. To make that API call, first you need to ask user permission by calling this part of your code:

   // this part is to ask permissions for user

   $loginUrl = "http://www.facebook.com/dialog/oauth?client_id=" . 
   $app_id . "&redirect_uri=" . urlencode($app_url) . "&scope=email";
   echo("<script> top.location.href='" . $loginUrl  . "'</script>");

只有在用户授予许可后，您才能通过调用代码的这一部分来获取用户的Facebook ID

Only after the user give permission, you can get the user Facebook ID by calling this part of your code

  $user_profile = $facebook->api('/me');