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Here is Kean's code, translated to VB. In case you missed it, I explained (briefly) how to handle the callback function in VB in the comments section of Kean's original post to Someone else who was having trouble. Of course the attached code already has it taken care of.
Dave O. 
I just wrote an article on creating own "MOVE" command with .NET API here:
http://drive-cad-with-code.blogspot.com/2011/01/creating-move-command-with-net-api.html
It also refers Kean's post, but intend to build a command behaving closely like AutoCAD built-in "MOVE" command.
The code is in C#. But it should be easily translated to VB.NET: "chiefbraincloud" has in the oter reply shown the translation of the tricky part: DragCallBack delegate.
If I understand you correctly, by "select multiple points", you mean Autocad's Point entity (DBPoint class), not geometric location ((x,y,z)). That is, you want pick a sieries of entities (DBPoints, or other entity type), after each pick, the selcted entity is highlighted, when picking next one, a rubber band line is drawn dynamically with the mouse cursor move while the next entity is to pick; the rubber band line starts from the last picked point (or somewhere of the last pciked entity). After the picking you would get a collection of ObjectId, or a collection of Point3d, or both.
If this what you want, obviously, the combination of PromptPointOption, which has BasePoint property that draws a rubber band line from a BasePoint, would not help you, because you need to use PromptEntityOption with Editor.GetEntity().
But it can certainly be done fairly easy with some code. It would be an interesting topic for another small article. I'll try it and get back in a day or two.
Well, if you meant to use Editor.GetPoint(), the PropmtPointOption class you use in conjunction with Editor.GetPoint() has properties UseBasePoint and BasePoint. Simply set former as "True" and set the latter to a Point3d (the last picked point), then Editor.GetPoint() draws a rubber band line for you while user is picking point. However, since you are picking point (geometric location), there is no entity that would be related to the picking that you can highlight as you wanted.
So, you must have something at the previously picked location there that can be highlighted. That "something", could be an existing entity that somehow has some association with the point picked; or you can draw some temporary visual stuff (yes, you can guess it: Transient Graphics would be the candidate) at picked points during the picking.
I did worte an article over the weekend on the former (if it would be of any help to you):
http://drive-cad-with-code.blogspot.com/2011/01/picking-entity-like-picking-point-with.html
For the latter, I could post something latter.
Also, since your goal is to pick points to form a region (e.g. to get a closed polyline visually), it might be better to not just showing the rubber band line from the last picked point. You might want to draw a polyline, starting from the first picked point, and extend it with each point added.
OK, I just compiled a quick blog post that might be what you needed here:
http://drive-cad-with-code.blogspot.com/2011/01/picking-points-with-visual-aid.html
BTW, to all possible readers:
I am not trying to promote my blog here. I just feel sometimes an appropriate answer to a question posted here might be too long, too complicated to post all code in a reply. In this case, I'd redirect the answer to my blog. Otherwise I'd just write short code snippet directly in the reply.
Hi Yuan,
That's exactly what i needed. Great blog again.
This is gonna help me out a lot.
Kudos for Yuan.
But i've got an other brain theaser. And it's not something i need but i think it supper cool how it works. And im verry intrested in how it works. But i havend got a clue how to create it.
Is it possible to create a command that works like the area command in AutoCAD. Here you also specify points. And also draw perimiter of the selected points but also fils the area with a transparent color. Like in the picture.
Yuan if you got some spare time i think you can help us out. These past articles you wrote are stuff where many beginning AutoCAD .net programmers can learn a lot from so are you up for the challenge?
Kind regards,
Irvin
The Netherlands
Thamks for your prompt of the bug: it is i the "try...finally{...}" block. I have correct lt in my blog, but here it is:
public void DoPick(bool drawTraceLine)
{
try
{
...
}
catch { }
finally
{
//Clear Transient graphics
if (_circles != null)
{ if (_circles.Count > 0)
{
foreach (Circle c in _circles)
{
TransientManager.CurrentTransientManager.
EraseTransient(c, new IntegerCollection());
c.Dispose();
}
}
_circles.Clear();
_circles = null;
}
ClearTraceLine();
}
}
Well, the "Area" commands in Acad2009 and Acad2011 (I skipped Acad2010) are slightly different: in Acad2009, it allows you get total area with only 2 points picked (obviously area=0), while in Acad2011, one must pick at least 3 points.
To fully mimic the "Area" command would be quite some work (with the command options of [Arc/Length...], especially the suboptions for the "Arc". But if only do points picking, it should be fairly easy to do.
I might be able to have some code for it, if I could manage a bit time.
Upated the code to show background color:
using System.Collections.Generic;
using Autodesk.AutoCAD.ApplicationServices;
using Autodesk.AutoCAD.EditorInput;
using Autodesk.AutoCAD.Geometry;
using Autodesk.AutoCAD.GraphicsInterface;
using Autodesk.AutoCAD.DatabaseServices;
namespace AreaCommand
{
public class MyAreaCmd
{
private Document _dwg;
private Editor _editor;
private double _area = 0.0;
private double _perimeter = 0.0;
private Autodesk.AutoCAD.DatabaseServices.Polyline _pline = null;
private Autodesk.AutoCAD.DatabaseServices.Hatch _hatch = null;
private List _points;
private bool _pickDone;
private Autodesk.AutoCAD.DatabaseServices.Transaction _tran = null;
private BlockTableRecord _model = null;
public MyAreaCmd(Document dwg)
{
_dwg = dwg;
_editor = _dwg.Editor;
}
public double Area
{
get { return _area; }
}
public double Perimeter
{
get { return _perimeter; }
}
public bool GetArea()
{
_pline=null;
//Pick first point
Point3d pt1;
if (!GetFirstPoint(out pt1)) return false;
//Pick second point
Point3d pt2;
if (!GetSecondPoint(pt1, out pt2)) return false;
_pickDone = false;
_points = new List();
_points.Add(new Point2d(pt1.X,pt1.Y));
_points.Add(new Point2d(pt2.X, pt2.Y));
try
{
_tran = _dwg.Database.TransactionManager.StartTransaction();
BlockTable bt = (BlockTable)_tran.GetObject(_dwg.Database.BlockTableId, OpenMode.ForRead);
_model = (BlockTableRecord)_tran.GetObject(bt[BlockTableRecord.ModelSpace], OpenMode.ForWrite);
//Handling mouse cursor moving during picking
_editor.PointMonitor +=
new PointMonitorEventHandler(_editor_PointMonitor);
while (true)
{
if (!PickNextPoint()) break;
}
if (_pline != null && _pickDone)
{
_area = _pline.Area;
_perimeter = _pline.Length;
}
}
catch
{
throw;
}
finally
{
ClearTransientGraphics();
//Remove PointMonitor handler
_editor.PointMonitor -=
new PointMonitorEventHandler(_editor_PointMonitor);
_tran.Abort();
_tran.Dispose();
_model = null;
}
return _pickDone;
}
#region private methods
private bool GetFirstPoint(out Point3d pt)
{
pt = new Point3d();
PromptPointOptions opt =
new PromptPointOptions("\nPick first corner: ");
PromptPointResult res = _editor.GetPoint(opt);
if (res.Status == PromptStatus.OK)
{
pt = res.Value;
return true;
}
else
{
return false;
}
}
private bool GetSecondPoint(Point3d basePt, out Point3d pt)
{
pt = new Point3d();
PromptPointOptions opt =
new PromptPointOptions("\nPick next corner: ");
opt.UseBasePoint = true;
opt.BasePoint = basePt;
PromptPointResult res = _editor.GetPoint(opt);
if (res.Status == PromptStatus.OK)
{
pt = res.Value;
return true;
}
else
{
return false;
}
}
private bool PickNextPoint()
{
PromptPointOptions opt =
new PromptPointOptions("\nPick next corner: ");
if (_points.Count > 2)
{
opt.Keywords.Add("Undo");
opt.Keywords.Add("Total");
opt.AppendKeywordsToMessage = true;
}
PromptPointResult res = _editor.GetPoint(opt);
if (res.Status == PromptStatus.OK)
{
_points.Add(new Point2d(res.Value.X,res.Value.Y));
return true;
}
else if (res.Status == PromptStatus.Keyword)
{
if (res.StringResult == "Undo")
{
if (_points.Count > 2)
{
_points.RemoveAt(_points.Count - 1);
}
return true;
}
else
{
_pickDone = true;
return false;
}
}
else
{
_pickDone = false;
return false;
}
}
private void ClearTransientGraphics()
{
if (_pline != null || _hatch!=null)
{
TransientManager.CurrentTransientManager.EraseTransients(
TransientDrawingMode.DirectTopmost,
128, new IntegerCollection());
if (_pline != null)
{
if (!_pline.IsErased) _pline.Erase();
_pline.Dispose();
_pline = null;
}
if (_hatch != null)
{
if (!_hatch.IsErased) _hatch.Erase();
_hatch.Dispose();
_hatch = null;
}
}
}
private void _editor_PointMonitor(object sender, PointMonitorEventArgs e)
{
ClearTransientGraphics();
//Draw polyline
Point2d pt = new Point2d(e.Context.RawPoint.X, e.Context.RawPoint.Y);
_pline = new Autodesk.AutoCAD.DatabaseServices.Polyline(_points.Count + 1);
for (int i = 0; i < _points.Count; i++)
{
_pline.AddVertexAt(i, _points[i], 0.0, 0.0, 0.0);
}
_pline.AddVertexAt(_points.Count, pt, 0.0, 0.0, 0.0);
_pline.Closed = true;
_model.AppendEntity(_pline);
_tran.AddNewlyCreatedDBObject(_pline, true);
TransientManager.CurrentTransientManager.AddTransient(
_pline, TransientDrawingMode.DirectTopmost,
128, new IntegerCollection());
_hatch = new Hatch();
_hatch.ColorIndex = 1; //set color to RED
_model.AppendEntity(_hatch);
_tran.AddNewlyCreatedDBObject(_hatch, true);
ObjectIdCollection loops = new ObjectIdCollection();
loops.Add(_pline.ObjectId);
_hatch.SetHatchPattern(HatchPatternType.PreDefined, "Solid");
_hatch.AppendLoop(HatchLoopTypes.Outermost, loops);
_hatch.EvaluateHatch(true);
TransientManager.CurrentTransientManager.AddTransient(
_hatch, TransientDrawingMode.DirectTopmost,
128, new IntegerCollection());
}
#endregion
}
}
Or you can go to the blog post, where the changed lines of code are highlighted in red:
http://drive-cad-with-code.blogspot.com/2011/01/mimicking-autocads-area-command-with_20.html
