@RequiresApi(api = Build.VERSION_CODES.O)
private void showNotification(){
    NotificationChannel notificationChannel=new NotificationChannel("channelId","channelName",NotificationManager.IMPORTANCE_HIGH);
    NotificationManager manager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
    Notification notification = new NotificationCompat.Builder(this).setContentText(getString(R.string.app_name))
            .setSmallIcon(R.mipmap.ic_launcher).setWhen(System.currentTimeMillis()).setContentTitle(getString(R.string.app_name))
            .setLargeIcon(BitmapFactory.decodeResource(getResources(),R.mipmap.ic_launcher))
            .setChannelId("channelId").setAutoCancel(false).build();
    manager.createNotificationChannel(notificationChannel);
    manager.notify(1001,notification);
}