Is user authorized, on Facebook tab

Getting an interesting error. I've been developing and application, and viewing it on it's page. Now I'm install that app in as tab on a company page and it's sayi开发者_JAVA技巧ng I can't use:

<fb:if-is-app-user>

in the tab view? How can I show or hide part of the page if the user viewing it is an app user?

FBML fan page tabs have been deprecated and replaced with Facebook iframe pages. To determine if the user is fan, you will need to decode the signed_request parameter that gets POST'ed to your webpage. There will be a "liked" variable in the encoded json payload. This page gives an example of how the new process works,