private void ButOK_Click(object sender, RoutedEventArgs e)
{
DateTime?begin = DpBegin.SelectedDate, end = DpEnd.SelectedDate;
if (begin != null && end != null)
{
Vac.BeginDate = begin.Value;
Vac.EndDate = end.Value;
}
Vac.UpdateVacation(ConnStr);
var wnd = this.Parent as Window;
wnd.Close();
}