卸载Class?
由于在Java中有一个可以自己替换的ClassLoader,所以在Eclipse中很容易管理成千上万的插件,可以在同一个应用域中自由地装载和卸载。在运行时为某个Class重新定义一个ClassLoader并且重新实例化,原来加载的东西就交给GC了。这个机制还有一个我一直梦想的一个价值就是在Load一个Class到应用域的时候运行某些方法,例如读出配置文件。如果配置文件中涉及到一些额外的Class需要更替就不必重新启动应用程序了。这对于需要类似热部署的场合非常有用。
在.net中没有这么幸运。Assembly是决不能被卸载的。有一个解决方案是通过卸载AppDomain的方式来卸载一系列的Assembly。经过一小番试验,跨域的调用是可以实现的,不过需要遵循一点点小规则。
一、只有自MashalByRefObject派生的类型可以跨应用域访问。因为Calling的域使用的中Executing域中的实例通过Unwrap出来的代理类,所以其实并不是真正的“跨应用域”,而是类似Remoting的方式。
二、所有传递的数据类型必须是加上Serializable Attribute的类型。
我的应用场景是通过选项在运行时替换一个已升级的Assembly依赖。这个依赖显然不能写到主应用程序所依赖的Assembly清单中,而是通过从配置文档读出其相关的Assembly并从指定位置加载。
下面的例子是读出一个Assembly中的所有类型并将其继承关系显示到一个TreeView中。
这是个用来传递类型信息的数据类型:
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