private void BtnEdit_Click(object sender, RoutedEventArgs e)
        {
            if (LvPrelimComponents.SelectedItem != null)
            {
                ViewModelLocator.SelectedSubjectViewModel.SelectedGradingPeriod = 0;
                ViewModelLocator.SelectedSubjectViewModel.IsEdit = true;
                var window = new AddActivityWindow();
                window.Owner = this;
                window.WindowStartupLocation = WindowStartupLocation.CenterOwner;

                ACTIVITY changedActivity = ViewModelLocator.SelectedSubjectViewModel.SelectedActivity as ACTIVITY;
                window.DataContext = changedActivity;

                var result = window.ShowDialog();
                if (result == true)
                {
                    ViewModelLocator.SelectedSubjectViewModel.EditActivity(changedActivity);
                }
            }
        }
        private void BtnAddComponent_Click(object sender, RoutedEventArgs e)
        {
            var window = new AddActivityWindow();

            window.Owner = this;
            window.WindowStartupLocation = WindowStartupLocation.CenterOwner;
            ViewModelLocator.SelectedSubjectViewModel.SelectedGradingPeriod = 0;
            ViewModelLocator.SelectedSubjectViewModel.IsEdit = false;

            ACTIVITY newActivity = new ACTIVITY();

            window.DataContext = newActivity;

            var result = window.ShowDialog();

            if (result == true)
            {
                ViewModelLocator.SelectedSubjectViewModel.AddActivity(newActivity);
            }
        }