Flex Error - ReferenceError：错误＃1065：未定义变量flash.external :: HostObject

Question

有没有人在Flash Builder 4.6和Extension Builder中遇到此错误。我相信我已经导入了所有正确的类，我在SDK和swc的

上使用默认值

代码：

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute" historyManagementEnabled="false">
    <mx:Script>
        <![CDATA[
            import flash.external.*;

            [Bindable]
            private var hostName:String = HostObject.mainExtension;

        ]]>
    </mx:Script>
    <mx:VBox height="100%" width="100%" verticalAlign="middle" horizontalAlign="center">
        <mx:Button label="Run PS code" click="TestPhotoshop.run()" enabled="{hostName.indexOf('photoshop') > -1}"/>
    </mx:VBox>
</mx:Application>