Flex TextArea滚动到底部

<mx:Script>
    <![CDATA[
    
        this.textarea.addEventListener(FlexEvent.VALUE_COMMIT,onValueCommit);

        private function onValueCommit(event:FlexEvent):void{ 

　　　　this.textarea.validateNow(); 

            this.textarea.verticalScrollPosition=this.textarea.maxVerticalScrollPosition;
        }
    ]]>
</mx:Script>


<mx:TextArea left="2" right="2" top="2" bottom="28" fontSize="12" editable="false" id="textarea">
    <mx:htmlText>
        <![CDATA[<b><font color='#FF0000'>Welcome to Flexchat!</font></b>]]>
    </mx:htmlText>

</mx:TextArea>

<object classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=7,0,19,0" width="585" height="186"><param name="movie" value="http://api.mtime.com/swf/list.swf"> <param name="quality" value="high"> <param name="wmode" value="transparent"> <param name="allowScriptAccess" value="always"> <param name="flashvars" value="title=%E7%94%B5%E5%BD%B1%E6%8E%A8%E8%8D%90&amp;stagewidth=200&amp;row=1&amp;col=6&amp;xmlUrl=http%3A%2F%2Fapi.mtime.com%2FWidget%2FMy%2FRatings%2F1692412%2F1%2F6"> <embed wmode="transparent" allowscriptaccess="always" src="http://api.mtime.com/swf/list.swf" quality="high" pluginspage="http://www.macromedia.com/go/getflashplayer" type="application/x-shockwave-flash" width="585" height="186" flashvars="title=%E7%94%B5%E5%BD%B1%E6%8E%A8%E8%8D%90&amp;stagewidth=200&amp;row=1&amp;col=6&amp;xmlUrl=http%3A%2F%2Fapi.mtime.com%2FWidget%2FMy%2FRatings%2F1692412%2F1%2F6"></embed></object>