IssueTracker

Looking at the source of BiometricPrompt it seems that it does not properly handle devices that are running API 28+ and do not have a fingerprint sensor.

Here is the if statement where the decision is made (line 716 of BiometricPrompt)

if (!shouldForceFingerprint && canUseBiometricFragment())

canUseBiometricFragment() only checks if the device is running API 28+ and shouldForceFingerprint is calculated mainly by shouldUseFingerprintforCrypto() . That method iterates through a list of devices that are considered not safe for crypto, all of them seem to be Samsung devices. The issue is that the code goes down the path of “I am running API 28 or grater so I am good to go” . This in turn tries to use the FingerprintManager class to get a string for the error during getErrorString(). This is null for our device since the hardware is not there. Devices that do not pass the if check from above (my Nexus 5 running API 23 for example) use the FingerprintHelperFragment and FingerprintDialogFragment classes to correctly handle not having a hardware sensor.

Here is the stacktrace of the issue:

Fatal Exception: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.hardware.fingerprint.FingerprintManager.getErrorString(int, int)' on a null object reference
       at android.hardware.biometrics.BiometricPrompt.lambda$sendError$0(BiometricPrompt.java:490)
       at android.hardware.biometrics.-$$Lambda$BiometricPrompt$HqBGXtBUWNc-v8NoHYsj2gLfaRw.run(-.java:6)
       at android.os.Handler.handleCallback(Handler.java:873)
       at android.os.Handler.dispatchMessage(Handler.java:99)
       at android.os.Looper.loop(Looper.java:193)
       at android.app.ActivityThread.main(ActivityThread.java:6725)
       at java.lang.reflect.Method.invoke(Method.java)
       at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:911)

The code should not use BiometricFragment for this scenario or if it does, BiometricFragment should check internally before using the FingerprintManager. Probably, the best solution is to have the code handle this case to use FingerprintHelperFragment and FingerprintDialogFragment.


library version: androidx.biometric:biometric:1.0.1
device: ATT Radiant (running Android 9.0 Go)