Apache flex 如何清除组的显式宽度和高度

我有一个组，它的大小与它包含的内容相符，但要使用Tweener执行转换，我必须设置宽度和高度属性。动画完成后，如何清除显式的宽度和高度属性，以便组返回到基于其内容的大小调整

之前：

<s:Group ><content.../></s:Group>

在tween之后，组有效地设置为500x500，就好像它是这样的：

<s:Group width="500" height="500" ><content /></s:Group>

我想让它回到这一点：

<s:Group ><content /></s:Group>

更新
使用Flextras的解决方案测试代码：

<fx:Script>
    <![CDATA[
        protected function button1_clickHandler(event:MouseEvent):void
        {
            var w:Object = myGroup.width;
            var h:Object = myGroup.height;

            if (myGroup.width!=300) {
                myGroup.width = 300;
                myGroup.height = 300;
            }
            else {
                myGroup.width = NaN;
                myGroup.height = NaN;

                w = myGroup.width; // NaN
                h = myGroup.height; // NaN

                //myGroup.validateNow()
                if (myGroup.parent is IInvalidating) {
                    IInvalidating(myGroup.parent).validateNow();
                }

                w = myGroup.width; // 600
                h = myGroup.height; // 100
            }


        }
    ]]>
</fx:Script>

<fx:Declarations>
    <!-- Place non-visual elements (e.g., services, value objects) here -->
</fx:Declarations>

<s:Group id="myGroup" minHeight="0" minWidth="0" clipAndEnableScrolling="true">     
    <s:Button width="600" height="100" label="here is a button" click="button1_clickHandler(event)"/>
</s:Group>

将高度和宽度设置为NaN；这将有效地告诉Flex框架“我不知道这个值是什么”，然后在组件下次呈现自身时执行measure（）事件；使其更新measuredHeight和measuredWidth属性；父容器将依次使用它来调整组的大小

将高度和宽度设置为NaN或Null？然后invalidateSize（）强制组重新计算？我没有尝试过。那就行了。：）如果你想得到分数，请添加答案。

<fx:Script>
    <![CDATA[
        protected function button1_clickHandler(event:MouseEvent):void
        {
            var w:Object = myGroup.width;
            var h:Object = myGroup.height;

            if (myGroup.width!=300) {
                myGroup.width = 300;
                myGroup.height = 300;
            }
            else {
                myGroup.width = NaN;
                myGroup.height = NaN;

                w = myGroup.width; // NaN
                h = myGroup.height; // NaN

                //myGroup.validateNow()
                if (myGroup.parent is IInvalidating) {
                    IInvalidating(myGroup.parent).validateNow();
                }

                w = myGroup.width; // 600
                h = myGroup.height; // 100
            }


        }
    ]]>
</fx:Script>

<fx:Declarations>
    <!-- Place non-visual elements (e.g., services, value objects) here -->
</fx:Declarations>

<s:Group id="myGroup" minHeight="0" minWidth="0" clipAndEnableScrolling="true">     
    <s:Button width="600" height="100" label="here is a button" click="button1_clickHandler(event)"/>
</s:Group>