[facebook app]Is there any way I can get the user_id from tab?

I'm trying to get user_id from the tab. I found out the params["signed_request"] will give me some info about the user_id. And I tried. But, in fact , params["signed_request"] gave me the wrong value. It returned the profile_id instead of user_id. Is there anyway I can get the user_id f开发者_运维百科rom tab?

You can only get a user's ID after they have interacted with the tab.