ObjectARX自定义实体的数据存储

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1. 众所周知自定义实体需要重写一些函数，其中关于自定义实体数据存储的两个：
   将自定义实体对象写入到DWG文件时调用的函数。
   virtual Acad::ErrorStatus dwgOutFields(AcDbDwgFiler* pFiler) const;
   从DWG文件中读取自定义实体对象时需要访问的函数。
   virtual Acad::ErrorStatus dwgInFields(AcDbDwgFiler* pFiler);
   如果自定义实体对象还要保存或读取DXF文件，则还需要重写：
   virtual Acad::ErrorStatus dxfInFields(AcDbDxfFiler* pFiler);
   virtual Acad::ErrorStatus dxfOutFields(AcDbDxfFiler* pFiler) const;

2. 创建三角形的自定义实体的数据存储的实现如下：
   实现dwgOut函数，向导生成了一些代码，我们要做的仅仅是把成员变量写入到外部：
   Acad::ErrorStatus dwgOutFields (AcDbDwgFiler *pFiler) const
   {
   assertReadEnabled () ;
   //—– Save parent class information first.
   Acad::ErrorStatus es =AcDbEntity::dwgOutFields (pFiler) ;
   if ( es != Acad::eOk )
   return (es) ;
   //—– Object version number needs to be saved first
   if ( (es =pFiler->writeUInt32 (kCurrentVersionNumber)) != Acad::eOk )
   return (es) ;
   //—– Output params
   for (int i = 0; i < 3; i++)
   {
   pFiler->writeItem(m_verts[i]);
   }

   return (pFiler->filerStatus ()) ;
   

   }

   实现dwgIn函数，我们要做的仅仅是从外部读取成员变量的值：
   Acad::ErrorStatus dwgInFields (AcDbDwgFiler *pFiler) {
   assertWriteEnabled () ;
   //—– Read parent class information first.
   Acad::ErrorStatus es =AcDbEntity::dwgInFields (pFiler) ;
   if ( es != Acad::eOk )
   return (es) ;
   //—– Object version number needs to be read first
   Adesk::UInt32 version =0 ;
   if ( (es =pFiler->readUInt32 (&version)) != Acad::eOk )
   return (es) ;
   if ( version > kCurrentVersionNumber )
   return (Acad::eMakeMeProxy) ;
   //- Uncomment the 2 following lines if your current object implementation cannot
   //- support previous version of that object.
   //if ( version < kCurrentVersionNumber )
   // return (Acad::eMakeMeProxy) ;
   //—– Read params
   for (int i = 0; i < 3; i++)
   {
   pFiler->readItem(&m_verts[i]);
   }
   return (pFiler->filerStatus ()) ;
   }