How to check whether the FACEID has been disallowed by the user in iOS App?

Question

When a Touch ID enabled App is first run on iPhone X the user is asked if they want to use Face ID instead. If they decline then Face ID is disabled and the user is never again given the option to use the feature. Short of deleting and re-installing the App is there another way to enable Face ID? The Image for permission is shown below:

Please tell once I press "Don't allow" and again when I use the application how to check that the permission has not been granted earlier? Based on that I can ask the user to enable by going to settings page but as of now I am stuck on how to determine whether the permission was denied earlier.

Answer 1

Short of deleting and re-installing the App is there another way to enable Face ID?

Settings -> your App -> Face ID

Please tell once I press "Don't allow" and again when I use the application how to check that the permission has not been granted earlier?

If the following returns FALSE.

if ([myContext canEvaluatePolicy:LAPolicyDeviceOwnerAuthenticationWithBiometrics error:&authError]) {