How do I find out all users who have installed my canvas app ? Is there a U开发者_Python百科I on Facebook for it or do I need to query an API ?
See https://developers.facebook.com/docs/reference/fql/insights/#Metrics
You can check the application_installed_users value to figure out how many users have installed your app.
EDIT: this requires the use of the Facebook FQL interface, as covered at https://developers.facebook.com/docs/reference/fql/
It can't be done as per this - How to get all the user IDs of people who are using your Facebook application
I would suggest use you to use the depreceated REST API call once to save all the IDs of the users, and then add a new user to that list (keep on saving it in a db).
精彩评论