How can I make sure that someone has successfully "liked" my site when they press the "like" button on my site?

I am developing a rails 3 app that needs to have to a facebook "like" button and display the profile pictures of the people who have click it and complete the liking process (logging into facebook, etc). For other reasons, my app needs to know when the @current_user has successfully liked my site. For instance, if they click the button but they aren't logged in to fac开发者_如何学Goebook and never bother to log in to facebook to complete the process, my app should not think that they liked my site. What's the easiest way to do this? I'd appreciate any help.

Attach to the Facebook javascript event using FB.Event.subscribe

FB.Event.subscribe('edge.create', function(response) {
  // fire an ajax call to store that the user has liked you
});

edge.create -- fired when the user likes something (fb:like)

http://developers.facebook.com/docs/reference/javascript/FB.Event.subscribe