The current primary sort key's column.
If non-null, indicates that the indicated column is the column by which the data is sorted. The number must correspond to the index of the relevant column in columns.
Setting this will cause the relevant column to have a sort indicator displayed.
When this is null, it implies that the table's sort order does not correspond to any of the columns.
The direction of the sort is specified using sortAscending.
final int? sortColumnIndex;