ios8 TouchID detection if fingerprint was added

In short; no.

In a bit more detail; the LocalAuthentication framework is a tightly-guarded black box. The information you get back from it is very limited. Your interaction with it goes something like this:

• Ask it if it's able to authenticate for some type of policy (there is only 1 available at time of writing - Biometrics (Touch ID))
• If it can, ask it to actually do it
• The system takes over for the actual authentication
• It lets you know if the authentication was successful or not (if not, it tells you why)

You have no concept of the actual authentication process (which finger was used, for example). This, of course, is by design. Apple does not want, nor need, to give you access to such information.

This is now possible in iOS9. The property evaluatedPolicyDomainState has been added to LAContext.

If the fingerprint database is modified (fingers were added or removed), the data returned by evaluatedPolicyDomainState will change. The nature of the changes cannot be determined but by comparing data of evaluatedPolicyDomainState after different evaluatePolicy calls you can detect that the set of fingerprints has been modified.

Note that this property is set only when evaluatePolicy is called and a succesful Touch ID authentication was performed, or when canEvaluatePolicy succeeds for a biometric policy.

As Keith stated, in iOS 9 it's possible. You should do it like this.

    let context = LAContext()
    context.canEvaluatePolicy(.DeviceOwnerAuthenticationWithBiometrics, error: nil)

    if let domainState = context.evaluatedPolicyDomainState
        where domainState == oldDomainState  {
        // Enrollment state the same

    } else {
        // Enrollment state changed

    }

Every time you add or delete a fingerprint, the domain state changes. You need to call canEvaluatePolicy for evaluatedPolicyDomainStateto be updated.