Flex动态创建类对象

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自ActionScript 3开始，eval函数就被取消了，这样就不能像原来那样利用字符串动态的创建对象了，但利用函数flash.utils.getDefinitionByName仍可以根据类型名称动态地创建类对象实例，下面看一个例子：

<?xml version="1.0" encoding="utf-8"?><mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute" minWidth="955" minHeight="600" applicationComplete="application1_applicationCompleteHandler(event)"> <mx:Script>  </mx:Script></mx:Application>package test{ public dynamic class DynamicObject { public function DynamicObject() { trace("DynamicObject is created!"); } }}

输出结果：

DynamicObject is created!DynamicObject is created!

其实这样的输出结果，没什么意外的。接下来将“new DynamicObject();”注释掉继续执行，以下是输出解决：

ReferenceError: Error #1065: Variable DynamicObject is not defined.at global/flash.utils::getDefinitionByName()at TestMain/application1_applicationCompleteHandler()[C:/Documents and Settings/Administrator/My Documents/Workspace/eclipse/ccgc/src/TestMain.mxml:14]at TestMain/___TestMain_Application1_applicationComplete()[C:/Documents and Settings/Administrator/My Documents/Workspace/eclipse/ccgc/src/TestMain.mxml:2]at flash.events::EventDispatcher/dispatchEventFunction()at flash.events::EventDispatcher/dispatchEvent()at mx.core::UIComponent/dispatchEvent()at mx.managers::SystemManager/preloader_preloaderDoneHandler()[C:/autobuild/3.5.0/frameworks/projects/framework/src/mx/managers/SystemManager.as:3140]at flash.events::EventDispatcher/dispatchEventFunction()at flash.events::EventDispatcher/dispatchEvent()at mx.preloaders::Preloader/displayClassCompleteHandler()[C:/autobuild/3.5.0/frameworks/projects/framework/src/mx/preloaders/Preloader.as:435]at flash.events::EventDispatcher/dispatchEventFunction()at flash.events::EventDispatcher/dispatchEvent()at mx.preloaders::DownloadProgressBar/timerHandler()[C:/autobuild/3.5.0/frameworks/projects/framework/src/mx/preloaders/DownloadProgressBar.as:1451]at mx.preloaders::DownloadProgressBar/initCompleteHandler()[C:/autobuild/3.5.0/frameworks/projects/framework/src/mx/preloaders/DownloadProgressBar.as:1503]at flash.events::EventDispatcher/dispatchEventFunction()at flash.events::EventDispatcher/dispatchEvent()at mx.preloaders::Preloader/dispatchAppEndEvent()[C:/autobuild/3.5.0/frameworks/projects/framework/src/mx/preloaders/Preloader.as:291]at mx.preloaders::Preloader/appCreationCompleteHandler()[C:/autobuild/3.5.0/frameworks/projects/framework/src/mx/preloaders/Preloader.as:443]at flash.events::EventDispatcher/dispatchEventFunction()at flash.events::EventDispatcher/dispatchEvent()at mx.core::UIComponent/dispatchEvent()at mx.core::UIComponent/set initialized()at mx.managers::LayoutManager/doPhasedInstantiation()at Function/http://adobe.com/AS3/2006/builtin::apply()at mx.core::UIComponent/callLaterDispatcher2()at mx.core::UIComponent/callLaterDispatcher()

之所以会出错，是因为在Flex编译程序时会自行删除一些未使用的，这时在动态创建对象时就会因缺失对象的类型而创建失败。之前的代码之所以执行成功，是因为类型DynamicObject在代码中显示地被使用，所以类型信息DynamicObject在编译时不会被删除。

其实还有一种方法来保证类型信息的存在，就是利用编译参数，也可以保证程序正常执行：
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