Notification.kt

 private fun sendNotification(messageBody: String) {
        val channelId = getString(R.string.default_notification_channel_id)
        val defaultSoundUri = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION)
        val notificationBuilder = NotificationCompat.Builder(this, channelId)
            .setSmallIcon(R.drawable.ic_stat_name)
            .setContentTitle(getString(R.string.fcm_message))
            .setContentText(messageBody)
            .setAutoCancel(true)
            .setSound(defaultSoundUri)

        val notificationManager = getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager

        // Since android Oreo notification channel is needed.
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            val channel = NotificationChannel(channelId,
                "Water Drop",
                NotificationManager.IMPORTANCE_HIGH)
            notificationManager.createNotificationChannel(channel)
        }
        notificationBuilder.build().flags.and(Notification.FLAG_AUTO_CANCEL)
        notificationManager.notify(0 /* ID of notification */, notificationBuilder.build())
    }