private lateinit var appUpdateManager: AppUpdateManager        // in app update
private val updateType = AppUpdateType.IMMEDIATE                // in app update

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

    //in app update
    appUpdateManager = AppUpdateManagerFactory.create(applicationContext)

    if (updateType == AppUpdateType.FLEXIBLE){
        appUpdateManager.registerListener(installStateUpdatedListener)
    }

    checkForAppUpdates()


}

private val installStateUpdatedListener = InstallStateUpdatedListener { state ->
    if (state.installStatus() == InstallStatus.DOWNLOADED) {
        Toast.makeText(
            applicationContext,
            "Download successful, Restarting app in 5 seconds",
            Toast.LENGTH_LONG
        ).show()

            appUpdateManager.completeUpdate()

    }


}

//in app update
private fun checkForAppUpdates() {

    appUpdateManager.appUpdateInfo.addOnSuccessListener { info ->
        val isUpdateAvailable = info.updateAvailability() == UpdateAvailability.UPDATE_AVAILABLE

        val isUpdateAllowed = when (updateType) {
            AppUpdateType.FLEXIBLE -> info.isFlexibleUpdateAllowed
            AppUpdateType.IMMEDIATE -> info.isImmediateUpdateAllowed
            else -> false
        }

        if (isUpdateAvailable && isUpdateAllowed) {
            appUpdateManager.startUpdateFlowForResult(
                info,
                updateType,
                this,
                123
            )
        }
    }
}


//in app update
override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
    super.onActivityResult(requestCode, resultCode, data)
    if (requestCode == 123) {
        if (resultCode != RESULT_OK) {
            // Handle update failure
            println("something went wrong ...")
        }
    }
}

//in app update
override fun onResume() {
    super.onResume()
    if (updateType == AppUpdateType.IMMEDIATE) {
        appUpdateManager.appUpdateInfo.addOnSuccessListener { info ->
            if (info.updateAvailability() == UpdateAvailability.DEVELOPER_TRIGGERED_UPDATE_IN_PROGRESS) {

                appUpdateManager.startUpdateFlowForResult(
                    info,
                    updateType,
                    this,
                    123
                )
            }

        }

    }
}

override fun onDestroy() {
    super.onDestroy()
    if (updateType == AppUpdateType.FLEXIBLE){
        appUpdateManager.unregisterListener(installStateUpdatedListener)
    }
}