Using permament running service in android

Question

I am creating a privacy task calendar. It uses an alarm manager and notifications. When the application is closed, the alarm service is apparently running and causing notifications. The notification has two actions - "set as completed" and "cancel". When I click "set as completed" in my task manager, there is nothing in the task list, because memory was freed, because the application is closed. A null pointer exception occurs.

Is it normal to use a constantly running service to store data, where you can set a task as completed?

Am I correct in understanding that WhatsApp uses a constantly running service with incoming message listener?

P.S. Sorry for my bad English. It's Google translate.

I cannot use the database, because it is encrypted. Only when I open the application, it is decrypted, and the task list is loaded into RAM.

I cannot use shared preferences, because there is a possibility of an information leak when connecting to a PC.

UPD:

TaskManager

    public Task getTaskById(int id) {
    Log.d("TaskCalendarLog", "Task manager getByID: task id = " + id);
    int index = 0;
    Log.d("TaskCalendarLog", "Task list = " + taskList);
    for (Task task:taskList) {//  <------- null pointer exception in taskList
        Log.d("TaskCalendarLog", "Task manager for: id = " + id);
        if (task.getId() == id) {
            return taskList.get(index);
        }
        index++;
    }
    return null;
}

TaskAlarmReciever

        Intent setDoneIntent = new Intent(context, ActionSetTaskDoneBroadcastReceiver.class);
    setDoneIntent.putExtra("id", taskId);
    PendingIntent setDonePendingIntent = PendingIntent.getBroadcast(context, 0, setDoneIntent, PendingIntent.FLAG_CANCEL_CURRENT | PendingIntent.FLAG_IMMUTABLE);

    NotificationCompat.Action cancel = new NotificationCompat.Action(R.drawable.ic_cancel, "Cancel", cancelPendingIntent);
    NotificationCompat.Action setDone = new NotificationCompat.Action(R.drawable.ic_done, "Set done", setDonePendingIntent);
    NotificationCompat.Builder notificationBuilder = new NotificationCompat.Builder(context, "TaskNotificationChannel")
            .setSmallIcon(R.drawable.ic_alarm)
            .setContentTitle("Task is now")
            .setContentText(taskText)
            .setGroup(GROUP_KEY_ALARM)
            .setPriority(NotificationCompat.PRIORITY_MAX)
            .setFullScreenIntent(taskAlarmPendingIntent, true)
            .setChannelId("TaskAlarmChannel")
            .addAction(cancel)
            .addAction(setDone)
            .setVibrate(new long[] {100, 100, 200, 200, 300, 300, 400, 400, 500, 500, 400, 400, 300, 300, 200, 200, 100})
            .setAllowSystemGeneratedContextualActions(true)
            .setStyle(new NotificationCompat.BigTextStyle().bigText(taskText))
            .setCategory(NotificationCompat.CATEGORY_CALL)
            .setAutoCancel(true);

ActionSetTaskDoneBroadcastReciever

    public void onReceive(Context context, Intent intent) {
    int id = intent.getIntExtra("id", 0);
    TaskManager taskManager = TaskManager.getInstance();
    Log.d("TaskCalendarLog", "Action: task id = " + id);
    taskManager.getTaskById(id).setIsDone("true");
    TaskApplication.getInstance().restartAllTaskAlarm();

    Intent taskRintoneServiceIntent = new Intent(context, RingtoneService.class);
    context.stopService(taskRintoneServiceIntent);

    NotificationManager notificationManager = (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);
    Log.d("TaskCalendarLog", "Notification id: " + id);
    notificationManager.cancel(id);
}