Flex Gumbo中如何通过skinClass样式去掉Spark Panel下拉阴影的例子

下面是main.mxml：<?xml version="1.0" encoding="utf-8"?> 
<s:Application name="Spark_Panel_skinClass_dropShadow_test" 
        xmlns:fx="http://ns.adobe.com/mxml/2009" 
        xmlns:s="library://ns.adobe.com/flex/spark"> 
  
    <s:Panel title="Spark Panel title" 
            skinClass="skins.CustomPanelSkin_noDropShadow" 
            width="200" 
            horizontalCenter="0" 
            verticalCenter="0"> 
        <s:VGroup left="20" right="20" top="20" bottom="20"> 
            <s:RichEditableText id="richEditableTxt" 
                    text="The quick brown fox jumps over the lazy dog." 
                    width="100%" 
                    height="100%" /> 
        </s:VGroup> 
    </s:Panel> 
  
</s:Application>

下面是CustomFxPanelSkin_noDropShadow.mxml的代码：<?xml version="1.0" encoding="utf-8"?> 
<s:SparkSkin name="CustomPanelSkin_noDropShadow" 
        xmlns:fx="http://ns.adobe.com/mxml/2009" 
        xmlns:s="library://ns.adobe.com/flex/spark" 
        alpha.disabled="0.5"> 
    <s:states> 
        <s:State name="normal" /> 
        <s:State name="disabled" /> 
    </s:states> 
  
    <fx:Metadata> 
    <![CDATA[ 
        [HostComponent("spark.components.Panel")] 
    ]]> 
    </fx:Metadata> 
  
    <fx:Script> 
        /* Define the skin elements that should not be colorized. 
           For panel, border and title backround are skinned, but the content area and title text are not. */ 
        static private const exclusions:Array = ["background", "titleField", "contentGroup"]; 
  
        override public function get colorizeExclusions():Array {return exclusions;} 
  
        /* Define the content fill items that should be colored by the "contentBackgroundColor" style. */ 
        static private const contentFill:Array = ["bgFill"]; 
  
        override public function get contentItems():Array {return contentFill}; 
    </fx:Script> 
  
    <!-- layer 1: border --> 
    <s:Rect left="0" right="0" top="0" bottom="0"> 
        <s:stroke> 
            <s:SolidColorStroke color="0" alpha="0.50" weight="1" /> 
        </s:stroke> 
    </s:Rect> 
  
    <!-- layer 2: background fill --> 
    <!--- Defines the appearance of the PanelSkin class's background. --> 
    <s:Rect id="background" left="1" top="1" right="1" bottom="1"> 
        <s:fill> 
        <!--- Defines the  PanelSkin class's background fill. The default color is 0xFFFFFF. --> 
            <s:SolidColor color="0xFFFFFF" id="bgFill" /> 
        </s:fill> 
    </s:Rect> 
  
    <!-- layer 3: title bar fill --> 
    <s:Rect left="1" right="1" top="1" height="30"> 
       <s:fill> 
            <s:LinearGradient rotation="90"> 
                <s:GradientEntry color="0xE2E2E2" /> 
                <s:GradientEntry color="0xD9D9D9" /> 
            </s:LinearGradient> 
       </s:fill> 
    </s:Rect> 
  
    <!-- layer 4: title bar highlight --> 
    <s:Rect left="1" right="1" top="1" height="30"> 
       <s:stroke> 
            <s:LinearGradientStroke rotation="90" weight="1"> 
                <s:GradientEntry color="0xEAEAEA" /> 
                <s:GradientEntry color="0xD9D9D9" /> 
            </s:LinearGradientStroke> 
       </s:stroke> 
    </s:Rect> 
    <s:Rect left="1" right="1" top="31" height="1"> 
        <s:fill> 
            <s:SolidColor color="0xC0C0C0" /> 
        </s:fill> 
    </s:Rect> 
  
    <!-- layer 5: text --> 
    <!--- Defines the appearance of the PanelSkin class's title bar. --> 
    <s:SimpleText id="titleField" lineBreak="explicit" 
             left="10" right="4" top="2" height="30" 
             verticalAlign="middle" fontWeight="bold" /> 
  
    <s:Group id="contentGroup" 
            left="1" right="1" top="32" bottom="1" /> 
  
</s:SparkSkin>