#region "System Imports"
using System;
using System.Collections.Generic;
using System.Text;
#endregion

#region "AutoCAD Imports"
using Autodesk.AutoCAD.Runtime;
using Autodesk.AutoCAD.ApplicationServices;
using Autodesk.AutoCAD.DatabaseServices;
using Autodesk.AutoCAD.Geometry;
using Autodesk.AutoCAD.EditorInput;
using Autodesk.AutoCAD.Colors;
#endregion

// import accoremgd.dll for A2013
[assembly: CommandClass(typeof(YourProjectName.AddExtraAttribute))]

namespace YourProjectName
{
    class AddExtraAttribute
    {
 
        [CommandMethod("nea", CommandFlags.Modal)]
        public static void AddNewAtt()
        {
            string blkName = "PART";
            Document doc = Autodesk.AutoCAD.ApplicationServices.Application.DocumentManager.MdiActiveDocument;
            Database db = doc.Database;
            Editor ed = doc.Editor;
            using (Transaction tr = db.TransactionManager.StartTransaction())
            {
                BlockTable bt = (BlockTable)tr.GetObject(db.BlockTableId, OpenMode.ForRead, false);

                if (!bt.Has(blkName))
                {
                    ed.WriteMessage("\nBlock definition TEST does not  exist");
                    return;
                }

                double dx = new double();
                double dy = new double();
                BlockTableRecord btr = (BlockTableRecord)tr.GetObject(bt[blkName], OpenMode.ForRead, false);

                int cnt = 0;
                AttributeDefinition matchAtt = new AttributeDefinition();
                foreach (ObjectId adefId in btr)
                {
                    DBObject attObj = (DBObject)tr.GetObject(adefId, OpenMode.ForRead, false);

                    if (attObj.GetRXClass().Name == "AcDbAttributeDefinition")
                    {
                        AttributeDefinition attObjDef = attObj as AttributeDefinition;
                        if (cnt == 0)
                        {
                            matchAtt = attObjDef;
                            dx = matchAtt.Position.X;
                            dy = matchAtt.Position.Y;
                            cnt += 1;
                        }
                        if (attObjDef != null)
                        {
                            Point3d ip = attObjDef.Position;
                            if ((attObjDef.Position.X >= dx) && (attObjDef.Position.Y <= dy))
                            {
                                dx = attObjDef.Position.X;
                                dy = attObjDef.Position.Y;
                            }
                        }
                    }
                }


                // get a location of the last AttributeDefinition in the 
                // block definition
                Point3d Oldloc = matchAtt.Position;
                double attTxtHeight = matchAtt.Height;
                
                // calculate location of the new AttributeDefinition in the 
                // block definition 

                Point3d ptNewloc = new Point3d(dx, dy - attTxtHeight * 1.97, btr.Origin.Z) + btr.Origin.GetAsVector();
                //// create a AttributeDefinition
                // specify the text,tag and prompt

                string strValue = "[ Enter a new value here ]";

                string strTag = "[ Enter a new tag here ]";

                string strPrompt = "[ Enter a new prompt here ]";
                // used text style of the last attribute definition
                AttributeDefinition attDef = new AttributeDefinition(ptNewloc, strValue, strTag, strPrompt, matchAtt.TextStyleId);
                attDef.Height = matchAtt.Height;
                attDef.Layer = "0";
                attDef.Color = Autodesk.AutoCAD.Colors.Color.FromColorIndex(ColorMethod.ByAci, 0);
                attDef.LinetypeId = matchAtt.LinetypeId;
                attDef.Height = matchAtt.Height;
                attDef.TextStyleId = matchAtt.TextStyleId;

                attDef.Annotative = matchAtt.Annotative;
                attDef.Preset = matchAtt.Preset;
                attDef.Invisible = matchAtt.Invisible;
                attDef.Constant = matchAtt.Constant;
                attDef.Justify = matchAtt.Justify;
                attDef.AlignmentPoint = ptNewloc;
                attDef.LockPositionInBlock = matchAtt.LockPositionInBlock;
                attDef.AdjustAlignment(db);
                // append the AttributeDefinition to the definition 
                btr.UpgradeOpen();
                btr.AppendEntity(attDef);
                tr.AddNewlyCreatedDBObject(attDef, true);
                btr.DowngradeOpen();

                tr.Commit();

                ed.WriteMessage("nPerform \"_ATTSYNC _N " + blkName + "\" + command manually");

            }
        }
    }
}