Kean-An automatic numbering system for AutoCAD blocks using .NET

using Autodesk.AutoCAD.ApplicationServices;
using Autodesk.AutoCAD.Runtime;
using Autodesk.AutoCAD.DatabaseServices;
using Autodesk.AutoCAD.EditorInput;
using Autodesk.AutoCAD.Geometry;
using System.Collections.Generic;
namespace AutoNumberedBubbles
{
  public class Commands : IExtensionApplication
  {
    // Strings identifying the block
    // and the attribute name to use
    const string blockName = "BUBBLE";
    const string attbName = "NUMBER";
    // In this version, just use a simple
    // integer to take care of the numbering
    private int m_bulletNumber = 0;
    // Constructor
    public Commands()
    {
    }
    // Functions called on initialization & termination
    public void Initialize()
    {
      try
      {
        Document doc =
          Application.DocumentManager.MdiActiveDocument;
        Editor ed = doc.Editor;
        ed.WriteMessage(
          "\nBAP  Create bubbles at points" +
          "\nBIC  Create bubbles at the center of circles"
        );
      }
      catch
      { }
    }
    public void Terminate()
    {
    }
    // Command to create bubbles at points selected
    // by the user - loops until cancelled
    [CommandMethod("BAP")]
    public void BubblesAtPoints()
    {
      Document doc =
        Application.DocumentManager.MdiActiveDocument;
      Database db = doc.Database;
      Editor ed = doc.Editor;
      Autodesk.AutoCAD.ApplicationServices.
      TransactionManager tm =
        doc.TransactionManager;
      Transaction tr =
        tm.StartTransaction();
      using (tr)
      {
        // Get the information about the block
        // and attribute definitions we care about
        BlockTableRecord ms;
        ObjectId blockId;
        AttributeDefinition ad;
        List other;
        if (GetBlock(
              db, tr, out ms, out blockId
          ))
        {
          GetBlockAttributes(
            tr, blockId, out ad, out other
          );
          // By default the modelspace is returned to
          // us in read-only state
          ms.UpgradeOpen();
          // Loop until cancelled
          bool finished = false;
          while (!finished)
          {
            PromptPointOptions ppo =
              new PromptPointOptions("\nSelect point: ");
            ppo.AllowNone = true;
            PromptPointResult ppr =
              ed.GetPoint(ppo);
            if (ppr.Status != PromptStatus.OK)
              finished = true;
            else
              // Call a function to create our bubble
              CreateNumberedBubbleAtPoint(
                db, ms, tr, ppr.Value,
                blockId, ad, other
              );
            tm.QueueForGraphicsFlush();
            tm.FlushGraphics();
          }
        }
        tr.Commit();
      }
    }
    // Command to create a bubble at the center of
    // each of the selected circles
    [CommandMethod("BIC")]
    public void BubblesInCircles()
    {
      Document doc =
        Application.DocumentManager.MdiActiveDocument;
      Database db = doc.Database;
      Editor ed = doc.Editor;
      // Allow the user to select circles
      TypedValue[] tvs =
        new TypedValue[1] {
            new TypedValue(
              (int)DxfCode.Start,
              "CIRCLE"
            )
          };
      SelectionFilter sf =
        new SelectionFilter(tvs);
      PromptSelectionResult psr =
        ed.GetSelection(sf);
      if (psr.Status == PromptStatus.OK &&
          psr.Value.Count > 0)
      {
        Transaction tr =
          db.TransactionManager.StartTransaction();
        using (tr)
        {
          // Get the information about the block
          // and attribute definitions we care about
          BlockTableRecord ms;
          ObjectId blockId;
          AttributeDefinition ad;
          List other;
          if (GetBlock(
                db, tr, out ms, out blockId
            ))
          {
            GetBlockAttributes(
              tr, blockId, out ad, out other
            );
            // By default the modelspace is returned to
            // us in read-only state
            ms.UpgradeOpen();
            foreach (SelectedObject o in psr.Value)
            {
              // For each circle in the selected list...
              DBObject obj =
                tr.GetObject(o.ObjectId, OpenMode.ForRead);
              Circle c = obj as Circle;
              if (c == null)
                ed.WriteMessage(
                  "\nObject selected is not a circle."
                );
              else
                // Call our numbering function, passing the
                // center of the circle
                CreateNumberedBubbleAtPoint(
                  db, ms, tr, c.Center,
                  blockId, ad, other
                );
            }
          }
          tr.Commit();
        }
      }
    }
    // Internal helper function to open and retrieve
    // the model-space and the block def we care about
    private bool
      GetBlock(
        Database db,
        Transaction tr,
        out BlockTableRecord ms,
        out ObjectId blockId
      )
    {
      BlockTable bt =
        (BlockTable)tr.GetObject(
          db.BlockTableId,
          OpenMode.ForRead
        );
      if (!bt.Has(blockName))
      {
        Document doc =
          Application.DocumentManager.MdiActiveDocument;
        Editor ed = doc.Editor;
        ed.WriteMessage(
          "\nCannot find block definition "" +
          blockName +
          "" in the current drawing."
        );
        blockId = ObjectId.Null;
        ms = null;
        return false;
      }
      ms =
        (BlockTableRecord)tr.GetObject(
          bt[BlockTableRecord.ModelSpace],
          OpenMode.ForRead
        );
      blockId = bt[blockName];
      return true;
    }
    // Internal helper function to retrieve
    // attribute info from our block
    // (we return the main attribute def
    // and then all the "others")
    private void
      GetBlockAttributes(
        Transaction tr,
        ObjectId blockId,
        out AttributeDefinition ad,
        out List other
      )
    {
      BlockTableRecord blk =
        (BlockTableRecord)tr.GetObject(
          blockId,
          OpenMode.ForRead
        );
      ad = null;
      other =
        new List();
      foreach (ObjectId attId in blk)
      {
        DBObject obj =
          (DBObject)tr.GetObject(
            attId,
            OpenMode.ForRead
          );
        AttributeDefinition ad2 =
          obj as AttributeDefinition;
        if (ad2 != null)
        {
          if (ad2.Tag == attbName)
          {
            if (ad2.Constant)
            {
              Document doc =
                Application.DocumentManager.MdiActiveDocument;
              Editor ed = doc.Editor;
              ed.WriteMessage(
                "\nAttribute to change is constant!"
              );
            }
            else
              ad = ad2;
          }
          else
            if (!ad2.Constant)
              other.Add(ad2);
        }
      }
    }
    // Internal helper function to create a bubble
    // at a particular point
    private Entity
      CreateNumberedBubbleAtPoint(
        Database db,
        BlockTableRecord btr,
        Transaction tr,
        Point3d pt,
        ObjectId blockId,
        AttributeDefinition ad,
        List other
      )
    {
      //  Create a new block reference
      BlockReference br =
        new BlockReference(pt, blockId);
      // Add it to the database
      br.SetDatabaseDefaults();
      ObjectId blockRefId = btr.AppendEntity(br);
      tr.AddNewlyCreatedDBObject(br, true);
      // Create an attribute reference for our main
      // attribute definition (where we'll put the
      // bubble's number)
      AttributeReference ar =
        new AttributeReference();
      // Add it to the database, and set its position, etc.
      ar.SetDatabaseDefaults();
      ar.SetAttributeFromBlock(ad, br.BlockTransform);
      ar.Position =
        ad.Position.TransformBy(br.BlockTransform);
      ar.Tag = ad.Tag;
      // Set the bubble's number
      int bubbleNumber =
        ++m_bulletNumber;
      ar.TextString = bubbleNumber.ToString();
      ar.AdjustAlignment(db);
      // Add the attribute to the block reference
      br.AttributeCollection.AppendAttribute(ar);
      tr.AddNewlyCreatedDBObject(ar, true);
      // Now we add attribute references for the
      // other attribute definitions
      foreach (AttributeDefinition ad2 in other)
      {
        AttributeReference ar2 =
          new AttributeReference();
        ar2.SetAttributeFromBlock(ad2, br.BlockTransform);
        ar2.Position =
          ad2.Position.TransformBy(br.BlockTransform);
        ar2.Tag = ad2.Tag;
        ar2.TextString = ad2.TextString;
        ar2.AdjustAlignment(db);
        br.AttributeCollection.AppendAttribute(ar2);
        tr.AddNewlyCreatedDBObject(ar2, true);
      }
      return br;
    }
  }
}

You can see only two commands have been implemented, for now: BAP (Bubbles At Points) and BIC (Bubbles In Circles). These commands will create bubbles in increasing order, starting at 1. For now there's nothing in the application to allow the numbering to continue when you reload the drawing - it will start again at 1, for now.
Here's a base drawing containing some circles (which you can download from here):
Here's what happens when we run the BIC command, selecting each of the circles, going from left to right:
And here's what happens after we run the BAP command, selecting a number of points at random:
In the next post we'll add some intelligence to the numbering system, by adding a class to take care of a lot of the hard work for us. We'll then implement some commands to use this class to get more control over the numbering.