Data in the editor's dropdown can be sorted against a single column and this is specified by the SortColumnIndex property. This property indicates the column's visible index in the dropdown. The visible index of a specific column can be obtained via the LookUpColumnInfoCollection.VisibleIndexOf method of the Columns object.
To apply sorting to a column the column's sort order must be specified via the
LookUpColumnInfo.SortOrder property. If it's set to
DevExpress.Data.ColumnSortOrder.None data isn't sorted. If it's set to
DevExpress.Data.ColumnSortOrder.Ascending or
DevExpress.Data.ColumnSortOrder.Descending data is sorted in ascending or descending order.
To enable end-users to sort by columns by clicking their headers set the HeaderClickMode property to HeaderClickMode.Sorting.