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。