How to detect whether a list is scrolling or not?

Is there any way to detect whether a list is scrolling or not,lik开发者_如何学JAVAelist.isScrolling

So, @Khaled showed a way to do it with the MX component. If you are using the Spark component, that event doesn't work. Instead, you can listen to changes on myList.scroller.viewport.verticalScrollPosition or horizontalScrollPosition.

<fx:Declarations>
    <fx:int id="scrollingCount" />
</fx:Declarations>

<s:initialize>
    BindingUtils.bindSetter(function(x:*):void { scrollingCount++; }, myList.scroller.viewport, "verticalScrollPosition");
</s:initialize>

<s:VGroup>
    <s:Label text="Scrolling: {scrollingCount}" />
    <s:List id="myList" height="200" dataProvider="{myData}" />
</s:VGroup>

In neither of these cases do you get to know when the list stops getting scrolled (I'm not sure if you want it or not). You might have to set a timer and any time the timer goes off without any scrolling events, you are no longer scrolling?

Unfortunately, you haven't explained what you are trying to accomplish, wo we can't adequately answer your question.

Or you can do somme thing like this in a list itemrenderer :

import spark.components.List;

[Bindable]
private var calcWidth:Number=195;   
private var listVerticalScroll:Boolean;
private var listHorizontalScroll:Boolean;

override protected function updateDisplayList(unscaledWidth:Number, unscaledHeight:Number):void{
    var ownerVerticalScroll:Boolean=List(owner).scroller.verticalScrollBar.visible;
    var ownerHorizontalScroll:Boolean=List(owner).scroller.horizontalScrollBar.visible;
    if(ownerVerticalScroll!=listVerticalScroll){
        listVerticalScroll=ownerVerticalScroll;
        scrollBarChange()
    }

    super.updateDisplayList(unscaledWidth,unscaledHeight);
}

private function scrollBarChange():void {       
    if(listVerticalScroll){
        var newWidth:Number=195-(listVerticalScroll?15:0);
        calcWidth=newWidth;
    }
}

you can use the ScrollEvent.SCROLL :

import mx.events.ScrollEvent

myList.addEventListener(ScrollEvent.SCROLL, scrollHandler);

function scrollHandler(e:ScrollEvent):void
{
//myList is scrolling
}

Or you can do it like this for spark component!

http://blog.flexexamples.com/2009/05/31/detecting-when-the-vertical-scroll-bar-is-scrolled-on-a-spark-list-control-in-flex-4/ -->

    <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 gap="0"
                        horizontalAlign="contentJustify"
                        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>