internal void Add(BaseViewItemHomeworkExam viewItemHomeworkOrExam)
        {
            if (viewItemHomeworkOrExam is ViewItemHomework)
            {
                (viewItemHomeworkOrExam as ViewItemHomework).Class = this;
            }
            else if (viewItemHomeworkOrExam is ViewItemExam)
            {
                (viewItemHomeworkOrExam as ViewItemExam).Class = this;
            }

            HandleWeightCategoryForHomeworkExam(viewItemHomeworkOrExam);

            if (HomeworkAndExams != null)
            {
                HomeworkAndExams.InsertSorted(viewItemHomeworkOrExam);
            }
        }
 internal void Remove(BaseViewItemHomeworkExam viewItemHomeworkOrExam)
 {
     HomeworkAndExams?.Remove(viewItemHomeworkOrExam);
 }