pressing cancel on the biometric prompt crashes the app, Error type - java.lang.NullPointerException

Issue

Only the cancel button crashes the app.
Normal authentication is working properly
Touching outside the prompt also dismisses the prompt.
But touching the cancel button crashes the application.
Also, I don't have any nullable or lateinit variables declared.

here's the stack trace -

2022-04-17 12:29:57.279 15888-15888/com.kenetic.blockchainvs E/ic.blockchainv: [qarth_debug:]  get PatchStore::createDisableExceptionQarthFile method fail.
2022-04-17 12:29:57.282 15888-15888/com.kenetic.blockchainvs E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.kenetic.blockchainvs, PID: 15888
    java.lang.NullPointerException: Parameter specified as non-null is null: method kotlin.jvm.internal.Intrinsics.checkNotNullParameter, parameter <anonymous parameter 0>
        at com.kenetic.blockchainvs.fingerprint.FingerPrintAuthentication.verifyBiometrics$lambda-0(Unknown Source:2)
        at com.kenetic.blockchainvs.fingerprint.FingerPrintAuthentication.$r8$lambda$ms5jsHgjq-6k8P4aokBQ7-zcrrI(Unknown Source:0)
        at com.kenetic.blockchainvs.fingerprint.FingerPrintAuthentication$$ExternalSyntheticLambda0.onClick(Unknown Source:0)
        at android.hardware.biometrics.BiometricPrompt$1.lambda$onDialogDismissed$1(BiometricPrompt.java:226)
        at android.hardware.biometrics.-$$Lambda$BiometricPrompt$1$J5PqpiT8xZNiNN1gy9VraVgknaQ.run(Unknown Source:2)
        at android.os.Handler.handleCallback(Handler.java:907)
        at android.os.Handler.dispatchMessage(Handler.java:105)
        at android.os.Looper.loop(Looper.java:216)
        at android.app.ActivityThread.main(ActivityThread.java:7625)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:524)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:987)

here's the code -

TaskEnum -

enum class FingerPrintTaskEnum {
    LOGIN, TRANSACTION
}

FingerPrintAuthentication -

package com.kenetic.blockchainvs.fingerprint

import android.content.Context
import android.content.DialogInterface
import android.hardware.biometrics.BiometricPrompt
import android.os.Build
import android.os.CancellationSignal
import android.widget.Toast
import androidx.annotation.RequiresApi

private const val TAG = "FingerPrintAuthentication"

class FingerPrintAuthentication(
    private val context: Context,
    private val taskEnum: FingerPrintTaskEnum,
    private val task: () -> Unit
) {
    private val authenticationCallback: BiometricPrompt.AuthenticationCallback
        get() =
            @RequiresApi(Build.VERSION_CODES.P)
            object : BiometricPrompt.AuthenticationCallback() {
                override fun onAuthenticationError(errorCode: Int, errString: CharSequence?) {
                    super.onAuthenticationError(errorCode, errString)
                    Toast.makeText(
                        context,
                        "Authentication failed, ${taskEnum.name} Cannot Be Executed",
                        Toast.LENGTH_SHORT
                    ).show()
                }

                override fun onAuthenticationSucceeded(result: BiometricPrompt.AuthenticationResult?) {
                    super.onAuthenticationSucceeded(result)
                    task()
                }
            }

    @RequiresApi(Build.VERSION_CODES.P)
    fun verifyBiometrics() {
        val biometricPrompt = BiometricPrompt.Builder(context)
            .setTitle(taskEnum.name)
            .setSubtitle("Authentication Required To Proceed")
            .setDescription(
                when (taskEnum) {
                    FingerPrintTaskEnum.LOGIN -> "Login To Account Through Fingerprint"
                    FingerPrintTaskEnum.TRANSACTION -> "Scan Your Fingerprint\nTo Authenticate Transaction"
                }
            )
            .setNegativeButton("Cancel", context.mainExecutor) { _: DialogInterface, _: Int -> }
            .build()
        biometricPrompt.authenticate(
            getCancellationSignal(),
            context.mainExecutor,
            authenticationCallback
        )
    }

    private fun getCancellationSignal(): CancellationSignal {
        val cancellationSignal = CancellationSignal()
        cancellationSignal.setOnCancelListener {
            Toast.makeText(
                context, "Fingerprint Authentication Cancelled", Toast.LENGTH_SHORT
            ).show()
        }
        return cancellationSignal
    }
}

I have made calls to this class from fragments using requireContext()

Solution

Try changing:

.setNegativeButton("Cancel", context.mainExecutor) { _: DialogInterface, _: Int -> }

to:

.setNegativeButton("Cancel", context.mainExecutor) { _: DialogInterface?, _: Int -> }

(IOW, change DialogInterface to DialogInterface?)

Answered By - CommonsWare