void btnSaveBooking_Click(object sender, RoutedEventArgs e)
{
if (gvwBooking.SelectedItem != null)
{
_selectedBookingId = ((Booking)gvwBooking.SelectedItem).BookingId;
}
List <Booking> oldList = (List <Booking>)gvwBooking.ItemsSource;
List <Booking> saveList = oldList.Where(d => (d.IsChanged || d.NullableRecordId == null)).ToList();
Globals.IsBusy = true;
DataServiceHelper.SaveBookingAsync(saveList, SaveBookingCompleted);
}