         }
 
         // fields.length == 1, so the collection is sorted on a single field.
-        var sortField:SortField = fields[0];
+        var sortField:ISortField = fields[0];
         var n:int = _columns.length;
         sortIndex = -1;
         for (var i:int = 0; i < n; i++)

            return;

        var view:ICollectionView = ICollectionView(dataProvider);
        var sort:Sort = view.sort;
        if (!sort)
        {
            sortIndex = lastSortIndex = -1;

        // do the sort if we're allowed to
        if (c.sortable)
        {
            var s:ISort = collection.sort;
            var f:ISortField;
            if (s)
            {
                s.compareFunction = null;
