在Canvas Facebook应用程序中，您需要请求用户授权您的应用程序恢复他们的

In a Canvas Facebook app, you need to ask the user to authorize your application to recover their unique identifier (and some other stuff).

所有你可以得到的是用户的语言，如果他喜欢或不喜欢你的页面Canvas应用程序位于。就是这样。

All you can get without that is the langage of the user, and if he likes or not the page where you Canvas app is located. That's it.

是的，您需要他们登录到您的应用程序，然后您将能够访问其唯一标识符。否则你将总是得到一个NULL答案。

So yes, you need them to log in to your application, and then you will be able to access their unique identifier. Otherwise you will always get a NULL answer.

我通常使用他们的Javascript SDK来启动画布应用程序的登录弹出窗口，以便用户保持在同一个窗口。

I generaly use their Javascript SDK to fire the login popup in the canvas app, so that the user stays in the same windows.

我希望这会对您有所帮助！

I hope this will help you !