c# AutoCAD 操作交互

//cad调用命令 
[CommandMethod("ChangeColor")]

        public void ChangeColor()
        {
         //获取操作的cad文档
            Document doc=Autodesk.AutoCAD.ApplicationServices.Application.DocumentManager.MdiActiveDocument;

          //获取Cad中document中的数据
            Database db = doc.Database;

         //进行编辑操作，与cad操作交互
            Editor ed = doc.Editor;
            
            try
            {
                 //提示用户选择对象
                ObjectId id = ed.GetEntity("\n 请选择要改变颜色的对象").ObjectId;
                //开启事务处理
                using (Transaction trans = db.TransactionManager.StartTransaction())
                {
                    //以写的方式打开对对象
                    Entity ent = (Entity)trans.GetObject(id, OpenMode.ForWrite);
                    ent.ColorIndex = 200;
                    trans.Commit();
                }
            }
            catch (Autodesk.AutoCAD.Runtime.Exception ex)
            {
                switch (ex.ErrorStatus)
                {
                    case ErrorStatus.InvalidIndex:
                        ed.WriteMessage("\n输入的颜色值有误");
                        break;
                    case ErrorStatus.InvalidObjectId:
                        ed.WriteMessage("\n请选择对象");
                        break;
                    default:
                        ed.WriteMessage(ex.ErrorStatus.ToString());
                        break;
                }
                
                 
            }
        }