void btnOK_Click(object sender, RoutedEventArgs e)
{
if (ucBookingNew.CheckValidation())
{
Booking newBooking = ucBookingNew.GetSavedBooking();
DataServiceHelper.CheckExistBookingdAsync(newBooking.RoomId, newBooking.ContractDateStart.Value, newBooking.ContractDateEnd.Value, CheckExistBookingdCompleted);
}
}