eui.Button 上放置两张图片

有时按钮会有一个需求。放置一个按钮底图，按钮文字是特效字体，也是一张图。 

1   1个普通按钮

<e:Button label="" x="288" y="294">
        <e:skinName>
            <e:Skin states="up,down,disabled">
            <e:Image width="100%" height="100%" source="on_png" source.down="off_png"/>
            <e:Label id="labelDisplay" horizontalCenter="0" verticalCenter="0"/>
            </e:Skin>
        </e:skinName>
</e:Button>

2 可以在exml 按钮源码里加上一张图

<e:Button label="" x="263" y="240" anchorOffsetX="0" width="161" anchorOffsetY="0" height="57">
        <e:skinName>
            <e:Skin states="up,down,disabled">
            <e:Image width="100%" height="100%" source="on_png" source.down="off_png"/>
            <e:Image  source="btn_png" verticalCenter="0" horizontalCenter="0"/>
            <e:Label id="labelDisplay" horizontalCenter="0" verticalCenter="0"/>
            </e:Skin>
        </e:skinName>
    </e:Button>