FLEX实践—Error #1009 when use LinearAxis

问题描述：
FLEX应用中有三个states，通过下拉列表切换state，三个state中显示的控件分别为：datagrid，chart，datagrid/chart；
当由只显示表格的视图切换到只显示图表的视图时，出现以下的错误：
TypeError: Error #1009: 无法访问空对象引用的属性或方法。
at mx.charts.chartClasses::ChartLabel/updateDisplayList()[C:\work\flex\dmv_automation\projects\datavisualisation\src\mx\charts\chartClasses\ChartLabel.as:262]
at mx.core::UIComponent/validateDisplayList()[C:\autobuild\3.2.0\frameworks\projects\framework\src\mx\core\UIComponent.as:6351]
at mx.managers::LayoutManager/validateDisplayList()[C:\autobuild\3.2.0\frameworks\projects\framework\src\mx\managers\LayoutManager.as:622]
at mx.managers::LayoutManager/doPhasedInstantiation()[C:\autobuild\3.2.0\frameworks\projects\framework\src\mx\managers\LayoutManager.as:695]
at Function/http://adobe.com/AS3/2006/builtin::apply()
at mx.core::UIComponent/callLaterDispatcher2()[C:\autobuild\3.2.0\frameworks\projects\framework\src\mx\core\UIComponent.as:8628]
at mx.core::UIComponent/callLaterDispatcher()[C:\autobuild\3.2.0\frameworks\projects\framework\src\mx\core\UIComponent.as:8568]
at flash.utils::Timer/_timerDispatch()
at flash.utils::Timer/tick()

上网搜了一下，发现问题出在<mx:LinearAxis title="平均耗时"/>上
FLEX BUG描述请参考：https://bugs.adobe.com/jira/browse/FLEXDMV-2088
根据BUG ISSUE提供的解决方案，我采用了以下的方法：
创建 CustomerChartTitleRenderer
package mx.controls.extend.chart
{
import mx.charts.chartClasses.ChartLabel;
import mx.core.IDataRenderer;

public class CustomerChartTitleRenderer extends ChartLabel implements IDataRenderer
{
public function CustomerChartTitleRenderer()
{
}
override protected function updateDisplayList(unscaledWidth:Number, unscaledHeight:Number):void {
if (parent == null){
return;
}
super.updateDisplayList(unscaledWidth, unscaledHeight);
}
}
}

将mxml中

<mx:verticalAxis>
<mx:LinearAxis title="平均耗时"/>

</mx:verticalAxis>

修改为
<mx:verticalAxisRenderers>
<mx:AxisRenderer titleRenderer="mx.controls.extend.chart.CustomerChartTitleRenderer">
<mx:axis>
<mx:LinearAxis title="平均耗时"/>
</mx:axis>
</mx:AxisRenderer>

</mx:verticalAxisRenderers>

问题解决。