通过acdbblockreference 获得块名

     AcDbBlockReference *pBlkRef = AcDbBlockReference::cast(ent.object());
     AcDbObjectId pBlkTblRecId;
     pBlkTblRecId = pBlkRef->blockTableRecord();
     AcDbBlockTableRecord *pBlkTblRec;

     es = acdbOpenObject(pBlkTblRec, pBlkTblRecId, AcDb::kForRead);