skin

创建Skin可以继承自各个skin(见帮助)
如：继承ButtonSkin
重写(override) updateDisplayList方法
name变量为upSkin、overSkin、downSkin等。

private var backgroundFillColor:Number;
override protected function updateDisplayList(unscaleWidth:Number,unscaledHeight:Number):void{
    super.updateDisplayList(unscaleWidth,unscaledHeight);
    switch(name){
        case "upSkin":
            backgroundFillColor = 0x666666;
            break;
        case "overSkin":
            backgroundFillColor = 0xcccccc;
            break;
        case "downSkin":
            backgroundFillColor = 0xffffff;
            break;
    }

    graphics.clear();
    graphics.beginFill(backgroundFillColor);
    graphics.drawRoundRectComplex(0,0,unscaleWidth,unscaleHeigt,0,20,20,0);
    graphics.endFill();
}

在css中引用，将overSkin upSkin downSkin指向skin类：
Button{
    overSkin: ClassRefrence("skins.myButtonSkin")(类名)
    upSkin: ClassRefrence("skins.myButtonSkin")
    downSkin: ClassRefrence("skins.myButtonSkin")
}