对于CAD中的实体进行筛选等操作，常常会用到实体的XData属性，下面介绍一下实体的XData的增删改。

//XData的新增，修改跟新增一样，new一个ResultBuffer，赋值即可Document doc=Application.DocumentManager.MdiActiveDocument;using (DocumentLock dl = doc.LockDocument()){using (Transaction trans = doc.TransactionManager.StartTransaction()){DBObject obj=trans.GetObjectId(id,OpenMode.ForWrite);//id为要设置的实体的ObjectId，也可以对实体直接进行设置也就是obj可以为Polyline、BlockReference、MText、DBText、Hatch...string regAppName="YourAppName";//你的注册应用程序名RegAppTable rat = (RegAppTable)trans.GetObject(db.RegAppTableId, OpenMode.ForWrite, false);if (!rat.Has(regAppName)){rat.UpgradeOpen();RegAppTableRecord ratr = new RegAppTableRecord();ratr.Name = regAppName;rat.Add(ratr);trans.AddNewlyCreatedDBObject(ratr, true);}ResultBuffer resBuf = new ResultBuffer();resBuf.Add(new TypedValue(1001, regAppName)); resBuf.Add(new TypedValue(1000, "YourContents")); resBuf.Add(new TypedValue(1000, "YourContents")); obj.XData = resBuf;trans.Comit()}} //XData的删除Document doc=Application.DocumentManager.MdiActiveDocument;using (DocumentLock dl = doc.LockDocument()){using (Transaction trans = doc.TransactionManager.StartTransaction()){DBObject obj=trans.GetObjectId(id,OpenMode.ForWrite);//id为要设置的实体的ObjectId，也可以对实体直接进行设置也就是obj可以为Polyline、BlockReference、MText、DBText、Hatch...string regAppName="YourAppName";//你的注册应用程序名RegAppTable rat = (RegAppTable)trans.GetObject(db.RegAppTableId, OpenMode.ForWrite, false);if (!rat.Has(regAppName)){RegAppTableRecord ratr = (RegAppTableRecord)rat[regAppName].GetObject(OpenMode.ForWrite);ratr.Erase();}trans.Comit()}}