private void cmbGrade_SelectedIndexChanged(object sender, EventArgs e)
{
ClassController classController = new ClassController();
if (cmbGrade.SelectedValue == null)
{
;
}
else
{
var listClass = classController.GetListClass((decimal)cmbGrade.SelectedValue);
if (listClass.Count > 0)
{
cmbClass.DataSource = listClass;
}
}
}