private void UserControl_Loaded(object sender, RoutedEventArgs e)
 {
     if (FormMode == FormModes.Edit || FormMode == FormModes.View)
     {
         ClassDetail           = ClassRepo.FindByID(_classid);
         SelectedSubjectList   = ClassSubjectRepo.GetSelectedSubjects(_classid);
         UnSelectedSubjectList = ClassSubjectRepo.GetUnSelectedSubjects(_classid);
     }
     if (FormMode == FormModes.New)
     {
         UnSelectedSubjectList = SubjectRepo.GetAll();
     }
 }