// 1. PopControlService 를 상속받아 class 를 만듭니다.
public class YourControlService extends PopControlService {

    // 2. buildForegroundNotification 함수를
오버라이드 합니다.
    @Override
    protected Notification buildForegroundNotification(@NonNull String unitId, @NonNull PopNotificationConfig popNotificationConfig) {
        // 3. getPopPendingIntent 를 통해 click 시 Pop Icon 을 띄우는 기능을 하는 PendingIntent 를 만들 수 있습니다.Pop을 표시하는 PendingIntent (원형 아이콘ㅇ)
        PendingIntent popPendingIntent = getPopPendingIntent(unitId, this);

       PendingIntent popPendingIntent// = getPopPendingIntent(unitId, this);
필요에 따라 notificationChannel을 등록합니다.
        NotificationCompat.Builder builder;
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            // 4. 필요에 따라 notificationChannel 을 생성해 등록합니다.
            createNotificationChannelIfNeeded();
            builder = new NotificationCompat.Builder(this, NOTIFICATION_CHANNEL_ID);
        } else {
            builder = new NotificationCompat.Builder(this);
        }

        // 5. CustomContolService 에서Pop Service Notification 에 사용할 View 를 등록합니다.
        RemoteViews remoteView = new RemoteViews(getPackageName(), R.layout.view_custom_notification);
        builder.setSmallIcon(popNotificationConfig.getSmallIconResId())
                .setContent(remoteView)
                .setContentIntent(popPendingIntent)
                .setPriority(PRIORITY_LOW)
                .setShowWhen(false);
        if (popNotificationConfig.getColor() == null) {
            builder.setColor(popNotificationConfig.getColor());
        }
        return builder.build();
    }

    @TargetApi(Build.VERSION_CODES.O)
    private void createNotificationChannelIfNeeded() {
        final NotificationManager notificationManager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
        if (notificationManager.getNotificationChannel(NOTIFICATION_CHANNEL_ID) == null) {
            final NotificationChannel channel = new NotificationChannel(NOTIFICATION_CHANNEL_ID, NOTIFICATION_CHANNEL_NAME, NotificationManager.IMPORTANCE_LOW);
            channel.setShowBadge(false);
            notificationManager.createNotificationChannel(channel);
        }
    }
}