I don’t believe there is a way to show a sort arrow without refreshing the data provider. Or maybe there is, and I just don’t know about it (very likely).

If you haven’t found a solution yet (and are still reading comments), I suggest asking on the FlexCoders mailing list and seeing if anybody there has any ideas.

Peter

Not sure if this is the best solution, but it seems to work:

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white">

    <mx:Script>
        <![CDATA[
            import mx.events.DataGridEvent;

            private function dataGrid_headerRelease(evt:DataGridEvent):void {
                // Hang out a while, wait a frame.
                callLater(delayedSet, [evt]);
            }

            private function delayedSet(evt:DataGridEvent):void {
                lbl1.text = evt.dataField;
                lbl2.text = dataGrid.columns[evt.columnIndex].sortDescending;
            }
        ]]>
    </mx:Script>

    <mx:Array id="arr">
        <mx:Object idx="1" c1="One.1" c2="One.2" />
        <mx:Object idx="2" c1="Two.1" c2="Two.2" />
        <mx:Object idx="3" c1="Three.1" c2="Three.2" />
        <mx:Object idx="4" c1="Four.1" c2="Four.2" />
        <mx:Object idx="5" c1="Five.1" c2="Five.2" />
        <mx:Object idx="6" c1="Six.1" c2="Six.2" />
    </mx:Array>

    <mx:DataGrid id="dataGrid"
            dataProvider="{arr}"
            headerRelease="dataGrid_headerRelease(event);">
        <mx:columns>
            <mx:DataGridColumn dataField="idx" />
            <mx:DataGridColumn dataField="c1" />
            <mx:DataGridColumn dataField="c2" />
        </mx:columns>
    </mx:DataGrid>

    <mx:Form>
        <mx:FormItem label="dataField:">
            <mx:Label id="lbl1" />
        </mx:FormItem>
        <mx:FormItem label="sortDescending:">
            <mx:Label id="lbl2" />
        </mx:FormItem>
    </mx:Form>

</mx:Application>

If you use an ArrayCollection or XMLListCollection as a data provider, you may be able to access the collection’s underlying sort property and determine the sort order as well.

In fact, here’s what that would look like too:

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white">

    <mx:Script>
        <![CDATA[
            import mx.collections.SortField;
            import mx.events.DataGridEvent;

            private function dataGrid_headerRelease(evt:DataGridEvent):void {
                // Hang out a while, wait a frame.
                callLater(delayedSet, [evt]);
            }

            private function delayedSet(evt:DataGridEvent):void {
                var sortField:SortField = arrColl.sort.fields[0] as SortField;
                lbl1.text = sortField.name;
                lbl2.text = sortField.descending.toString();
            }
        ]]>
    </mx:Script>

    <mx:ArrayCollection id="arrColl">
        <mx:source>
            <mx:Array>
                <mx:Object idx="1" c1="One.1" c2="One.2" />
                <mx:Object idx="2" c1="Two.1" c2="Two.2" />
                <mx:Object idx="3" c1="Three.1" c2="Three.2" />
                <mx:Object idx="4" c1="Four.1" c2="Four.2" />
                <mx:Object idx="5" c1="Five.1" c2="Five.2" />
                <mx:Object idx="6" c1="Six.1" c2="Six.2" />
            </mx:Array>
        </mx:source>
    </mx:ArrayCollection>

    <mx:DataGrid id="dataGrid"
            dataProvider="{arrColl}"
            headerRelease="dataGrid_headerRelease(event);">
        <mx:columns>
            <mx:DataGridColumn dataField="idx" />
            <mx:DataGridColumn dataField="c1" />
            <mx:DataGridColumn dataField="c2" />
        </mx:columns>
    </mx:DataGrid>

    <mx:Form>
        <mx:FormItem label="dataField:">
            <mx:Label id="lbl1" />
        </mx:FormItem>
        <mx:FormItem label="sortDescending:">
            <mx:Label id="lbl2" />
        </mx:FormItem>
    </mx:Form>

</mx:Application>

Again, I make no claims this is the “best” approach, just the first thing that came to mind at 7:40am. :)

Peter