How to set a fallback method if fingerprint does not work

Question

I recently moved my project to AndroidX and while implementing fingerprint for the app I am using the Biometric for AndroidX.

implementation 'androidx.biometric:biometric:1.0.0-alpha03'

When a dialog is displayed to use fingerprint for authentication, the dialog has "Cancel" option set as the negative button.

 final BiometricPrompt.PromptInfo promptInfo = new BiometricPrompt.PromptInfo.Builder()
            .setTitle("Log into App")
            .setSubtitle("Please touch the fingerprint sensor to log you in")
            .setDescription("Touch Sensor")
            .setNegativeButtonText("Cancel".toUpperCase())
            .build();

As per the android documentation: https://developer.android.com/reference/androidx/biometric/BiometricPrompt.PromptInfo.Builder.html#setNegativeButtonText(java.lang.CharSequence)

Required: Set the text for the negative button. 
This would typically be used as a "Cancel" button, but may be also used
to show an alternative method for authentication, 
such as screen that asks for a backup password.

So instead of "Cancel" button I can say "Use Password" to provide an alternative method incase fingerprint fails, and when user clicks on it I can show another popup dialog where I can let user enter the device password to help retrieve the app password from the Keystore. Is this correct ?

But, what happens if I do not have password set to unlock my phone instead I use a pattern ?

I see that if I use android.hardware.biometrics.BiometricPrompt.Builder instead of androidx.biometric.BiometricPrompt.PromptInfo.Builder, it has a method https://developer.android.com/reference/android/hardware/biometrics/BiometricPrompt.Builder.html#setDeviceCredentialAllowed(boolean) for the same purpose, to let user authenticate using other means if fingerprint fails.

Can someone help me understand this ? How I could achieve this with AndroidX as my app is compatible from API 16 onwards. And why does AndroidX does not come back with this fallback method ?

Answer 1

The setDeviceCredentialAllowed API was recently added in beta01

See the release notes here

https://developer.android.com/jetpack/androidx/releases/biometric