How To Get Dynamic Block from Anonymous Block

By Madhukar Moogala

A common request from developers is how to retrieve the original Dynamic Block reference from a given anonymous block. This is useful when working with AutoCAD’s Dynamic Blocks, as modifying or identifying the source Dynamic Block definition can be critical in automation and customization workflows. AutoCAD stores a reference to the Dynamic Block inside an anonymous block using extended entity data (XData). The following C# function demonstrates how to extract this reference.

    
      public static Handle GetDynamicBlockHandleFromAnonymousBlock(BlockTableRecord btr)
      {
          if (!btr.IsAnonymous)
              return ObjectId.Null.Handle;
          Handle btrHand = btr.ObjectId.Handle;
          ResultBuffer rb = btr.GetXDataForApplication("AcDbBlockRepBTag");
          if (rb == null)
              return ObjectId.Null.Handle;
          foreach (TypedValue tv in rb)
          {
              if (tv.TypeCode == 1005 && tv.Value is string strValue)
                  {
                  long nHandle = Convert.ToInt64(strValue, 16);
                  return new Handle(nHandle);
                  }
          }
          return ObjectId.Null.Handle;
      }