private static void SelectedTrimesterChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            EntryTrimesterSubjectCommentsViewModel entryTrimesterSubjectComments = (EntryTrimesterSubjectCommentsViewModel)d;

            entryTrimesterSubjectComments.FromDate = MainViewModel.Instance.Parameters.Periods.Where(p => p.Trimester == entryTrimesterSubjectComments.SelectedTrimester).OrderBy(p => p.Number).First().FromDate;
            entryTrimesterSubjectComments.ToDate   = MainViewModel.Instance.Parameters.Periods.Where(p => p.Trimester == entryTrimesterSubjectComments.SelectedTrimester).OrderByDescending(p => p.Number).First().ToDate;
        }
        private static void SelectedClassChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            EntryTrimesterSubjectCommentsViewModel entryTrimesterSubjectComments = (EntryTrimesterSubjectCommentsViewModel)d;

            entryTrimesterSubjectComments.SelectedClassChangedEvent?.Invoke();
        }