对自定义XML文件的读、写、修改、删除操作，加入简单类工厂和单例模式，便于扩展。打包成DLL，EX为测试项-XML documents to read, write, modify, delete operations, adding a simple type of plant and single-case model, convenient for extension. Packaged into a DLL, EX test items

对自定义XML文件的读、写、修改、删除操作，加入简单类工厂和单例模式，便于扩展。打包成DLL，EX为测试项-XML documents to read, write, modify, delete operations, adding a simple type of plant and single-case model, convenient for extension. Packaged into a DLL, EX test items