Manipulating the draw order of a newly created AutoCAD hatch using .NET

This question came in from Limin as a comment in this previous post:

Is there .Net interface for autocad command "DrawOrder"? For example: after solid-hatch a polyline, need to reorder polyline and hatch, how to make it happen using .NET?

I've put together some C# code to demonstrate how to do this:

using Autodesk.AutoCAD.ApplicationServices;

using Autodesk.AutoCAD.DatabaseServices;

using Autodesk.AutoCAD.EditorInput;

using Autodesk.AutoCAD.Runtime;

namespace HatchDrawOrder

{

  public class Commands

  {

    [CommandMethod("HDO")]

    static public void HatchDrawOrder()

    {

      Document doc =

        Application.DocumentManager.MdiActiveDocument;

      Editor ed = doc.Editor;

      // Ask the user to select a hatch boundary

      PromptEntityOptions opt =

        new PromptEntityOptions(

          "\nSelect boundary: "

        );

      opt.SetRejectMessage("\nObject must be a curve.");

      opt.AddAllowedClass(typeof(Curve), false);

      PromptEntityResult res =

        ed.GetEntity(opt);

      if (res.Status == PromptStatus.OK)

      {

        Transaction tr =

          doc.TransactionManager.StartTransaction();

        using (tr)

        {

          // Check the entity is a closed curve

          DBObject obj =

            tr.GetObject(

              res.ObjectId,

              OpenMode.ForRead

            );

          Curve cur = obj as Curve;

          if (cur != null && cur.Closed == false)

          {

            ed.WriteMessage("\nLoop must be a closed curve.");

          }

          else

          {

            // Add the hatch to the model space

            BlockTable bt =

              (BlockTable)tr.GetObject(

                doc.Database.BlockTableId,

                OpenMode.ForRead

              );

            BlockTableRecord btr =

              (BlockTableRecord)tr.GetObject(

                bt[BlockTableRecord.ModelSpace],

                OpenMode.ForWrite

              );

            Hatch hat = new Hatch();

            hat.SetDatabaseDefaults();

            hat.SetHatchPattern(

              HatchPatternType.PreDefined,

              "SOLID"

            );

            ObjectId hatId = btr.AppendEntity(hat);

            tr.AddNewlyCreatedDBObject(hat, true);

            // Add the hatch loop and complete the hatch

            ObjectIdCollection ids =

              new ObjectIdCollection();

            ids.Add(res.ObjectId);

            hat.Associative = true;

            hat.AppendLoop(

              HatchLoopTypes.Default,

              ids

            );

            hat.EvaluateHatch(true);

            // Change the draworder of both hatch and loop

            btr.DowngradeOpen();

            ids.Add(hatId);

            DrawOrderTable dot =

              (DrawOrderTable)tr.GetObject(

                btr.DrawOrderTableId,

                OpenMode.ForWrite

              );

            dot.MoveToBottom(ids);

            tr.Commit();

          }

        }

      }

    }

  }

}

The code to manipulate the draw order of these two entities is very simple - we have to open the DrawOrderTable for the space containing the entities we care about, and use it to change the order in which the entities are drawn. In this case I chose to send them both to the back of the draw order stack, but you might also manipulate their draw order relative to other entities in the drawing.

On a personal note, my family and I have arrived safely in Beijing - we're all a bit jet-lagged, but very happy to be here. The journey was thankfully uneventful, and with two young children that's really as much as you can hope for. :-)