Simple Android Fingerprint authentication dialog

AppActivity.kt

package com.myapp.app.ui.auth

import android.os.Build
import android.os.Bundle
import android.support.v4.content.ContextCompat
import android.support.v7.app.AppCompatActivity
import android.view.Gravity
import android.view.MenuItem
import android.view.View
import android.view.WindowManager


class AuthActivity : AppCompatActivity(), AuthNavigator {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        // check if canAuthenticateWithFingerprint
        if (FingerprintAuthDialog.canAuthenticateWithFingerprint(this)) {
            FingerprintAuthDialog(this)
                    .setOnAuthenticationError { dialog, error ->
                      // authentication FingerprintAuthError error
                    }
                    .setOnAuthenticationSuccess { dialog ->
                        /// success
                    }
                    .show()
        }

    }
    
}

FingerprintAuthDialog.kt

package com.myapp.app.widget

import android.Manifest
import android.annotation.TargetApi
import android.app.Dialog
import android.app.KeyguardManager
import android.content.Context
import android.content.Context.KEYGUARD_SERVICE
import android.content.pm.PackageManager
import android.graphics.Color
import android.graphics.drawable.ColorDrawable
import android.os.Build
import android.support.v4.content.ContextCompat
import android.support.v4.hardware.fingerprint.FingerprintManagerCompat
import kotlinx.android.synthetic.main.fingerprint_dialog.*

class FingerprintAuthDialog(
        private val context: Context
): FingerprintManagerCompat.AuthenticationCallback() {

    enum class FingerprintAuthError {
        authError,
        authFailed,
        authHelp,
        fingerprintPermissionNotGranted,
        fingerprintHardwareNotDetected,
        hasNotEnrolledFingerprints,
        keyguardIsNotSecure
    }

    companion object {
        // return true if there is a fingerprint hardware, fingerprint registered and permissions to scan fingerprint
        fun canAuthenticateWithFingerprint(context: Context): Boolean {

            val fingerprintManager = FingerprintManagerCompat.from(context)
            val keyguardManager = context.getSystemService(KEYGUARD_SERVICE) as KeyguardManager

            return Build.VERSION.SDK_INT >= Build.VERSION_CODES.M
                    && fingerprintManager.isHardwareDetected
                    && ContextCompat.checkSelfPermission(context, Manifest.permission.USE_FINGERPRINT) == PackageManager.PERMISSION_GRANTED
                    && keyguardManager.isKeyguardSecure
                    && fingerprintManager.hasEnrolledFingerprints()
        }
    }

    private var fingerprintManager = FingerprintManagerCompat.from(context)
    private var keyguardManager = context.getSystemService(KEYGUARD_SERVICE) as KeyguardManager

    private val dialog = Dialog(context)

    private var onAuthenticationErrorCallback: ((dialog: Dialog, error: FingerprintAuthError) -> Unit)? = null
    private var onAuthenticationSuccessCallback: ((dialog: Dialog) -> Unit)? = null

    init {

        if(!fingerprintManager.isHardwareDetected) {
            onAuthenticationErrorCallback?.invoke(dialog, FingerprintAuthError.fingerprintHardwareNotDetected)
        } else if (ContextCompat.checkSelfPermission(context, Manifest.permission.USE_FINGERPRINT) != PackageManager.PERMISSION_GRANTED) {
            onAuthenticationErrorCallback?.invoke(dialog, FingerprintAuthError.fingerprintPermissionNotGranted)
        } else if (!keyguardManager.isKeyguardSecure) {
            onAuthenticationErrorCallback?.invoke(dialog, FingerprintAuthError.keyguardIsNotSecure)
        } else if (fingerprintManager.hasEnrolledFingerprints()) {
            onAuthenticationErrorCallback?.invoke(dialog, FingerprintAuthError.hasNotEnrolledFingerprints)
        }

    }

    /// callback when occurs some error
    fun setOnAuthenticationError(onAuthenticationError: ((dialog: Dialog, error: FingerprintAuthError) -> Unit)): FingerprintAuthDialog {
        this.onAuthenticationErrorCallback = onAuthenticationError
        return this
    }

    // callback when auth succeds
    fun setOnAuthenticationSuccess(onAuthenticationSuccess: (dialog: Dialog) -> Unit): FingerprintAuthDialog {
        this.onAuthenticationSuccessCallback = onAuthenticationSuccess
        return this
    }

    // show fingerprint authentication dialog
    @TargetApi(Build.VERSION_CODES.M)
    fun show() {
        dialog.setContentView(R.layout.fingerprint_dialog)
        dialog.window.setBackgroundDrawable(ColorDrawable(Color.TRANSPARENT))

        dialog.btCancel.setOnClickListener {
            dialog.dismiss()
        }

        dialog.show()

        // start listening for fingerprint scanner
        fingerprintManager.authenticate(null, 0, null, this, null)
    }


    /// FingerprintManagerCompat.AuthenticationCallback()
    /// ----------------------------------------------------

    override fun onAuthenticationSucceeded(result: FingerprintManagerCompat.AuthenticationResult?) {
        dialog.txtMessage.text = context.getString(R.string.fingerprint_auth_success)
        onAuthenticationSuccessCallback?.invoke(dialog)
    }

    override fun onAuthenticationError(errMsgId: Int, errString: CharSequence?) {
        dialog.txtMessage.text = context.getString(R.string.fingerprint_auth_error)
        onAuthenticationErrorCallback?.invoke(dialog, FingerprintAuthError.authError)
    }

    override fun onAuthenticationHelp(helpMsgId: Int, helpString: CharSequence?) {
        dialog.txtMessage.text = context.getString(R.string.fingerprint_auth_help)
        onAuthenticationErrorCallback?.invoke(dialog, FingerprintAuthError.authHelp)
    }

    override fun onAuthenticationFailed() {
        dialog.txtMessage.text = context.getString(R.string.fingerprint_auth_error)
        onAuthenticationErrorCallback?.invoke(dialog, FingerprintAuthError.authFailed)
    }

}