public AttendanceManualViewModel()
{
attendanceManager = new AttendanceManager();
attendanceManager.AttendanceFixed += AttendanceManager_AttendanceFixed;
attendanceManager.SubscriptionClosed += AttendanceManager_SubscriptionClosed;
messager = new Messager();
AttendancePrice = 30;
Groups = attendanceManager.GetGroups();
if (Groups.Count > 0)
{
SelectedGroup = Groups[0];
}
SelectedDate = DateTime.Today;
}