From Xojo Documentation
Used to get or set the sort direction for the passed column. The first column is numbered zero.
You set the sort direction using ListBox.SortDirections.
This example sets the sort direction for a column.
ColumnSortDirectionAt doesn't actually sort the rows; it only establishes the sort direction that is used when the Sort method is called. The sort direction can be set even if there is no header for the ListBox.
If you set ColumnSortDirectionAt to None, the user can't sort the column by clicking its header. This will block the usual calls to the SortColumn and CompareRows events.