flex 自定义LineChart的数据字段的显示格式 dataFunction

自定义LineChart的数据字段的显示格式：

<mx:LineChart id="linechart1" height="100%" width="100%" dataProvider="{ datasource }"
	showDataTips="true" seriesFilters="[]">
	<mx:horizontalAxis>
    	<mx:CategoryAxis displayName="结算周期" categoryField="settledate" labelFunction="setRegisterDateFormat2" dataFunction="dataFunc"/>
    </mx:horizontalAxis>
	<mx:series>
		<mx:LineSeries displayName="补贴金额" yField="subsidymoney"/>
		<mx:LineSeries displayName="消费金额" yField="salesmoney"/>
	</mx:series>
</mx:LineChart>

private function dataFunc( axis : CategoryAxis,item : Object ):Object {
            
	var df : DateFormatter = new DateFormatter();
	df.formatString = "YYYY-MM";
	return df.format( item.settledate );
}

private function setRegisterDateFormat2 ( item:Object,prevValue:Object,axis:CategoryAxis,categoryItem:Object ) : String {
	var df : DateFormatter = new DateFormatter();
	df.formatString = "YYYY-MM";
	return df.format( item );
}