How can I tell if a different finger was used to unlock an iOS phone?

问题

The iOS 9 release notes indicate that a second (or subsequent) unlock with the same finger will return a value. This is useful for determining if an iPhone may be shared among different users. ... and adapting PIN codes as necessary. (for example, a mother sharing a phone with a child, both are touch enrolled)

From the release notes:

Support for reusable Touch ID matches. A match from the previous phone unlock can be used by evaluateAccessControl: and evaluatePolicy:localizedReason:reply:.

How can I leverage this to detect a new login?

I think the core issue I'm having is that I'm using Xamarin, and perhaps not interpreting the code correctly.

来源：https://stackoverflow.com/questions/34640878/how-can-i-tell-if-a-different-finger-was-used-to-unlock-an-ios-phone