How to know user has removed my application from his page immediately?

I want to do something when who has removed my application from his page.

At that time, is there an API event that can开发者_如何学Go catch it?

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There 's the deauthorization callback. If you set the deauthorization callback on your application settings page, everytime a user remove your application, FB will post to your callback URL with that user Facebook ID. You can refer about it here, Application De-authorization part.