How to handle face id permission alert?

I had written the following code snippet


if ([contextNew canEvaluatePolicy:LAPolicyDeviceOwnerAuthenticationWithBiometrics error:&error])

{

[contextNew evaluatePolicy:LAPolicyDeviceOwnerAuthenticationWithBiometrics localizedReason:NSLocalizedString(@"",nil) reply:^(BOOL success, NSError *error)

{

if(success)

{

}

else

{

}

}

}


it comes in sucess block after verification of face.I want to handle face id permission alert.

Please reply as soon as possible