绑定CAD实体到AS单元

可以通过AS单元的用户自定义属性：UserAttribute【0-9】储存10个cad实体的信息，比如ID或者句柄，实现CAD实体到AS单元之间的关联绑定。

一、获取CAD实体句柄

    acEnt = acTrans.GetObject(result.ObjectId, OpenMode.ForWrite) as Entity; 
    string  string_Handle = acEnt.Handle.ToString(); //获取句柄并转换成字符串   
    arc = acTrans.GetObject(acEnt.ObjectId, OpenMode.ForWrite) as Arc;
    string  string_Handle = arc.ToString();  //获取句柄并转换成字符串      

二、将CAD实体句柄存储在AS单元的用户自定义属性：UserAttribute中

 IPolyBeam polyBeam = m_Joint.CreatePolyBeam(sectionClass, sectionSize, (Role)beamRole, polyline, vecRefOrientation, zVec);
 polyBeam.UserAttribute[1]=string_Handle;
 或者
 beam = obj as Autodesk.AdvanceSteel.Modelling.StraightBeam;
 beam.SetUserAttribute(1,string_Handle); 

三、读取AS单元中的用户自定义属性：UserAttribute值（CAD实体句柄）

    string string_Handle = polyBeam.UserAttribute[0];
    或者
    string string_Handle = beam.getAttributeStatus(0).ToString();

四、将CAD句柄（字符串）转换成实体ID

    public ObjectId GetObjectId(Database db, string handleString)
        {
            long l = Convert.ToInt64(handleString, 16);
            Handle handle = new Handle(l);
            return db.GetObjectId(false, handle, 0);
        }

五、通过ID访问CAD实体

    acEnt = acTrans.GetObject(result.ObjectId, OpenMode.ForWrite) as Entity;
    arc = acTrans.GetObject(acEnt.ObjectId, OpenMode.ForWrite) as Arc;