private void btnAttendanceSave_Click(object sender, RoutedEventArgs e)
 {
     if (SelectedDate.IsValidDate() && SelectedClassID > 0)
     {
         foreach (var item in StudentAttendanceList)
         {
             Attendance atnd = new Attendance {
                 ClassID = SelectedClassID, StudentID = SelectedStudenID, SessionID = SessionID, isPresent = item.isPresent, updated_by = UserID
             };
             if (item.isExisted)
             {
                 AttendanceRepo.Update(atnd);
             }
             else
             {
                 atnd.created_by = UserID;
                 AttendanceRepo.Insert(atnd);
             }
         }
     }
     else
     {
         Message(MessageTypes.Error, "Please Select the date and Class");
     }
 }