How to show a block when positioning it, using C#?

By Marat Mirgaleev

Issue

I want to insert a block showing it while the mouse is being moved until the block is placed. How can I do it?

Solution

You need to create a DrawJig-derived class and override its Sampler() and WorldDraw() methods.
When the WorldDraw() method is called, create a BlockReference instance in memory and pass it to the WorldDraw.Geometry.Draw() method.
The C# sample code below demonstrates this approach.
There is a "BlockJig" command defined in the code. It assumes that there is a block named "TEST" in the current drawing.
When the command is run the block is being previewed. When the user clicks the left mouse button, a block insert will be created.

using Autodesk.AutoCAD.Geometry;    using Autodesk.AutoCAD.DatabaseServices;    using Autodesk.AutoCAD.ApplicationServices;    using Autodesk.AutoCAD.EditorInput;    using Autodesk.AutoCAD.Runtime;              namespace MySamples    {           public class BlockJigCmds      {             // Ask the user to place the block named "TEST", showing it         //   during the dragging.        // Make sure that a block with this name exists in the drawing.        //===============================================================        [CommandMethod("BlockJig")]        static public void BlockJig()        {          Editor ed =                  Application.DocumentManager.MdiActiveDocument.Editor;          Database db = ed.Document.Database;          try          {            using (Transaction tr =                               db.TransactionManager.StartTransaction())            {              // Find the "TEST" block in the current drawing              BlockTable bt = (BlockTable)tr.GetObject(db.BlockTableId,                                                       OpenMode.ForRead);              BlockTableRecord block = (BlockTableRecord)tr.GetObject(                                           bt["TEST"], OpenMode.ForRead);                   // Create the Jig and ask the user to place the block           &#160
;  //----------------------------------------------------              MyBlockJig blockJig = new MyBlockJig();              Point3d point;              PromptResult res = blockJig.DragMe( block.ObjectId,                                                   out point);              if (res.Status == PromptStatus.OK)              {                // Now we need to do the usual steps to place                //   the block insert at the position where the user                 //   did the click                BlockTableRecord curSpace =                   (BlockTableRecord)tr.GetObject(                                   db.CurrentSpaceId, OpenMode.ForWrite);                BlockReference insert = new BlockReference(point,                                                         block.ObjectId);                curSpace.AppendEntity(insert);                tr.AddNewlyCreatedDBObject(insert, true);              }              tr.Commit();            } // using          }          catch (System.Exception ex)          {            ed.WriteMessage(ex.ToString());          }        } // BlockJig()           } // class BlockJigCmds                // This Jig will show the given block during the dragging.      //=================================================================      public class MyBlockJig : DrawJig      {        public Point3d _point;        private ObjectId _blockId = ObjectId.Null;             // Shows the block until the user clicks a point.        // The 1st parameter is the Id of the block definition.        // The 2nd is the clicked point.        //---------------------------------------------------------------        public PromptResult DragMe(ObjectId i_blockId, out Point3d o_pnt)        {          _blockId = i_blockId;          Editor ed =                   Application.DocumentManager.MdiActiveDocument.Editor;               PromptResult jigRes = ed.Drag(this);          o_pnt = _point;          return jigRes;        }                  // Need to override this method.        // Updating the current position of the block.        //--------------------------------------------------------------        protected override SamplerStatus Sampler(JigPrompts prompts)        {          JigPromptPointOptions jigOpts = new JigPromptPointOptions();          jigOpts.UserInputControls =                               (UserInputControls.Accept3dCoordinates |                                UserInputControls.NullResponseAccepted);          jigOpts.Message = "Select a point:";          PromptPointResult jigRes = prompts.AcquirePoint(jigOpts);               Point3d pt = jigRes.Value;          if (pt == _point)            return SamplerStatus.NoChange;               _point = pt;          if (jigRes.Status == PromptStatus.OK)            return SamplerStatus.OK;               return SamplerStatus.Cancel;        }                  // Need to override this method.    &#
160;   // We are showing our block in its current position here.        //--------------------------------------------------------------        protected override bool WorldDraw(                      Autodesk.AutoCAD.GraphicsInterface.WorldDraw draw)        {          BlockReference inMemoryBlockInsert =                                    new BlockReference(_point, _blockId);          draw.Geometry.Draw(inMemoryBlockInsert);               inMemoryBlockInsert.Dispose();               return true;        } // WorldDraw()           } // class BlockJig         } // namespace MySamples