在Flex4中要写一个Skin类，将它赋给button的skinClass属性

<?xml version="1.0" encoding="utf-8"?>
<s:Skin xmlns:s="library://ns.adobe.com/flex/spark" xmlns:fx="http://ns.adobe.com/mxml/2009"  width.down="100" height.down="26" width.disabled="100" height.disabled="26" width.over="100" height.over="26" width.up="100" height.up="26">
        <fx:Metadata>[HostComponent("spark.components.Button")]</fx:Metadata>
        <s:states>
                <s:State name="up"/>
                <s:State name="over"/>
                <s:State name="down"/>
                <s:State name="disabled"/>
        </s:states>
        <fx:DesignLayer>
                <s:BitmapImage smooth="true" source="@Embed('/assets/disabled.png')" visible.up="false" visible.over="false" visible.down="false"/>
                <s:BitmapImage smooth="true" source="@Embed('/assets/down.png')" visible.up="false"  visible.over="false" visible.disabled="false"/>
                <s:BitmapImage smooth="true" source="@Embed('/assets/over.png')"  visible.up="false" visible.down="false" visible.disabled="false"/>
                <s:BitmapImage smooth="true" source="@Embed('/assets/up.png')"  visible.over="false" visible.down="false" visible.disabled="false"/>
        </fx:DesignLayer>
        <s:RichText color="#fcfafa"
                                id="labelDisplay"
                                fontFamily="宋体"
                                fontSize="12"
                                x="0" y="0" width="100%" height="100%"
                       
                                lineHeight="150%"
                                whiteSpaceCollapse="preserve"
                                color.disabled="#333333"
                                tabStops.disabled="S0"  verticalAlign="middle" textAlign="center">
        </s:RichText>
</s:Skin>