Availability and biometry type¶

Why the user can not authenticate¶

canAuthenticate answers true or false. getAvailability answers the same question and tells why not, so your app can react:

final availability = await auth.getAvailability(
  method: AuthenticationMethod.biometricsOnly,
);

switch (availability) {
  case AuthenticationAvailability.available:
    // Offer biometric authentication.
  case AuthenticationAvailability.notEnrolled:
    // Ask the user to enroll, or allow the device credential.
  case AuthenticationAvailability.lockedOut:
    // Biometrics are locked, the device credential still works.
  default:
    // Offer another way in.
}

`AuthenticationAvailability`	Meaning
`available`	The user can authenticate. `canAuthenticate` is `true` only in this case.
`notAvailable`	The device has no hardware for the method, or it can not be used right now.
`notEnrolled`	The user did not enroll any biometrics.
`lockedOut`	Biometrics are locked out. Reported on iOS and macOS only.¹
`credentialNotSet`	The device has no PIN, pattern, passcode or password, and the method needs it.
`unsupportedMethod`	The platform does not support the method.

¹ Android only reports a lockout when authenticating, as the lockedOut reason of the AuthenticationException.

Falling back to the device credential¶

This is the most common use: prefer biometrics, and let users without them in with their PIN or password.

Future<AuthenticationMethod?> pickMethod(FlutterLocalAuthentication auth) async {
  final biometrics = await auth.getAvailability();
  if (biometrics == AuthenticationAvailability.available) {
    return AuthenticationMethod.biometricsOnly;
  }

  const fallback = AuthenticationMethod.biometricsOrDeviceCredential;
  if (await auth.canAuthenticate(method: fallback)) return fallback;

  return null; // Local Authentication is not available.
}

Labeling your UI¶

getBiometryType tells which kind of biometrics the device has, to show the right text and icon:

final label = switch (await auth.getBiometryType()) {
  BiometryType.face => 'Unlock with Face ID',
  BiometryType.fingerprint => 'Unlock with your fingerprint',
  BiometryType.iris => 'Unlock with Optic ID',
  BiometryType.multiple => 'Unlock with biometrics',
  BiometryType.none => 'Unlock',
};

`BiometryType`	iOS / macOS	Android	Linux
`fingerprint`	Touch ID	Fingerprint sensor	Fingerprint (`fprintd`)
`face`	Face ID	Face unlock hardware (Android 10+)	—
`iris`	Optic ID	Iris scanner (Android 10+)	—
`multiple`	—	More than one kind of hardware	—
`none`	No biometrics	No biometric hardware	No fingerprint available

It is about the hardware

The type tells what the device has, not what the user enrolled. On Android the system also decides which biometrics the prompt uses, so multiple is returned when there is more than one. Use getAvailability to know if the user can actually authenticate.