Keep sorting and sort arrows after datagrid dbprovider changed

Question

I followed this tutorial http://justinjmoses.wordpress.com/2008/06/26/flex-keeping-the-sort-on-a-datagrid-when-you- change-the-dataprovider/
created listeners
that keeps old sorting of datagrid after dataprovider changed, but displaying sort arrow on the wrong column(always the 1st column), how do I fix it?
                   //constructor
          public function FilterDatagrid()
               super();
               addEventListener(mx.events.CollectionEvent.COLLECTION_CHANGE, onDataGridDataChange, false, 0, true);
          private var currentSort:mx.collections.Sort;
          private function onDataGridDataChange(evt:CollectionEvent):void
               //get the new data collection
               var ac:ArrayCollection = this.dataProvider as ArrayCollection;
               //attach the collection change event
               ac.addEventListener(CollectionEvent.COLLECTION_CHANGE, onCollectionChanged,false,0,true);
               //if a sort was in place before the data was changed, make sure you apply the sort to this new data
               if (currentSort != null)
                    ac.sort = currentSort;
                    ac.refresh();
          private function onCollectionChanged(evt:CollectionEvent):void
               if (evt.kind == CollectionEventKind.REFRESH)
                    var ac:ArrayCollection = evt.currentTarget as ArrayCollection;
                    currentSort = ac.sort;

Answer 1

the datagrid uses XML as dataprovider and uses labelFunction and sortCompareFunction on each column, not sure if it matters