Detecting when the vertical scroll bar is scrolled on a Spark List control in Flex 4

The following example shows how you can detect when the vertical scroll bar is scrolled on a Spark List control in Flex 4 by listening for the change event on the List control’s VScrollBar instance.

Full code after the jump.

To use the following code, you must have Flash Player 10 and a Flex Gumbo SDK installed in your Flex Builder 3. For more information on downloading and installing the Gumbo SDK into Flex Builder 3, see “Using the beta Gumbo SDK in Flex Builder 3″. To download the latest build of the Flex Gumbo SDK, see http://opensource.adobe.com/wiki/display/flexsdk/Download+Flex+4.

View MXML

<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2009/05/31/detecting-when-the-vertical-scroll-bar-is-scrolled-on-a-spark-list-control-in-flex-4/ -->
<s:Application name="Spark_List_scroller_verticalScrollBar_change_test"
        xmlns:fx="http://ns.adobe.com/mxml/2009"
        xmlns:s="library://ns.adobe.com/flex/spark"
        xmlns:mx="library://ns.adobe.com/flex/halo">

    <fx:Script>
        <![CDATA[
            import spark.components.VScrollBar;

            private function init():void {
                list.scroller.verticalScrollBar.addEventListener(Event.CHANGE, list_verticalScrollBar_change);
            }

            private function list_verticalScrollBar_change(evt:Event):void {
                var vsb:VScrollBar = evt.currentTarget as VScrollBar;
                var obj:Object = {};
                obj.type = evt.type;
                obj.val = vsb.value;
                obj.max = vsb.maximum;
                arrColl.addItem(obj);
                callLater(dgScroll);
            }

            private function dgScroll():void {
                dataGrid.verticalScrollPosition = dataGrid.maxVerticalScrollPosition;
            }
        ]]>
    </fx:Script>

    <fx:Declarations>
        <mx:ArrayCollection id="arrColl" />
    </fx:Declarations>

    <s:HGroup horizontalCenter="0" verticalCenter="0">
        <s:List id="list"
                creationComplete="init();">
            <s:layout>
                <s:VerticalLayout requestedRowCount="4" />
            </s:layout>
            <s:dataProvider>
                <s:ArrayList>
                    <fx:String>The</fx:String>
                    <fx:String>Quick</fx:String>
                    <fx:String>Brown</fx:String>
                    <fx:String>Fox</fx:String>
                    <fx:String>Jumps</fx:String>
                    <fx:String>Over</fx:String>
                    <fx:String>The</fx:String>
                    <fx:String>Lazy</fx:String>
                    <fx:String>Dog</fx:String>
                </s:ArrayList>
            </s:dataProvider>
        </s:List>
        <mx:DataGrid id="dataGrid"
                dataProvider="{arrColl}"
                width="200"
                verticalScrollPolicy="on">
            <mx:columns>
                <mx:DataGridColumn dataField="type" />
                <mx:DataGridColumn dataField="val" />
                <mx:DataGridColumn dataField="max" />
            </mx:columns>
        </mx:DataGrid>
    </s:HGroup>

</s:Application>

View source is enabled in the following example.

This entry is based on a beta version of the Flex Gumbo SDK and therefore is very likely to change as development of the Flex SDK continues. The API can (and will) change causing examples to possibly not compile in newer versions of the Flex Gumbo SDK.

Tagged as: change, Gumbo, scroller, verticalScrollBar