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hi,
You cannot use an ename or a handle in a selection filter.
From the developer's documentation:
The ssget function recognizes all group codes except entity names (group code -1), handles (group code 5), and xdata (group codes greater than 1000)
On the other hand, you do not need to select entites you already know the ename or handle, just directly use the ename (possibly got from the handle with handent) or add it to an existing selection set with ssadd.
@serag.hassouna wrote:
.... a function ssfiltered, whose only argument is a previously made AutoLISP selection set (the filter selection set), and the function's task is to allow the user to interactively select objects on screen with a crossing window, and it selects only those objects that are elements in the filter selection set and reside in the crossing window.
.... the function will apply sssetfirst on the filter result.....
Will this do what you're after? It's not limited to using a single crossing window, but allows any kind of selection options, and when done, leaves you with only those selected objects selected/gripped/highlighted that were also in the 'ssbefore'-argument selection set.
(defun ssfiltered (ssbefore / ssnew n ent)
(prompt "\nTo get only objects from the existing-selection-set argument within a wider selection,")
(if (setq ssnew (ssget))
(progn ; then
(repeat (setq n (sslength ssnew))
(setq ent (ssname ssnew (setq n (1- n))))
(if (not (ssmemb ent ssbefore)) (ssdel ent ssnew))
); repeat
(sssetfirst nil ssnew)
); progn
); if
); defun
Kent Cooper, AIA 
Yes, with a small difference, it doesn't highlight the valid objects - in real time - when they're in the selection region.
But all in all, it's more compact & simple.
Really shame on me 
, instead of constructing a new ssget from the ground and thinking a lot about all the internal low level logic, I didn't think about using another ssget.
The .NET API provides the Editor.SelectionAdded event which allows to remove entities from the selction set in real time.
static PromptSelectionResult GetFilteredSelection(Editor ed, HashSet<ObjectId> allowed)
{
SelectionAddedEventHandler filter = (_, e) =>
{
var objs = e.AddedObjects;
for (int i = 0; i < objs.Count; i++)
{
if (!allowed.Contains(objs[i]))
e.Remove(i);
}
};
ed.SelectionAdded += filter;
var selection = ed.GetSelection();
ed.SelectionAdded -= filter;
return selection;
}
You can download the attached ZIP file, unblock it, extract the FilteredSelectionLispFunction.dll and NETLOAD it from AutoCAD.
It defines a new ssfiltered LISP function which requires a list of enames as arguments.
Testing example:
(while (setq e (car (entsel))) (setq l (cons e l))) (setq s (ssfiltered l)) (sssetfirst nil s)
The whole C# code defining the LISP function if you prefer compile it by yourself.
using System.Collections.Generic;
using Autodesk.AutoCAD.DatabaseServices;
using Autodesk.AutoCAD.EditorInput;
using Autodesk.AutoCAD.Runtime;
using AcAp = Autodesk.AutoCAD.ApplicationServices.Core.Application;
namespace FilteredSelectionLispFunction
{
public class LispFunctions
{
static TypedValue nil = new TypedValue((int)LispDataType.Nil);
[LispFunction("ssfiltered")]
public static TypedValue GetFilteredSelection(ResultBuffer resbuf)
{
if (resbuf == null) return nil;
var args = resbuf.AsArray();
var allowed = new HashSet<ObjectId>();
for (int i = 1; i < args.Length - 1; i++)
if (args[i].TypeCode == (int)LispDataType.ObjectId)
allowed.Add((ObjectId)args[i].Value);
if (allowed.Count == 0) return nil;
var ed = AcAp.DocumentManager.MdiActiveDocument.Editor;
SelectionAddedEventHandler filter = (_, e) =>
{
var objs = e.AddedObjects;
for (int i = 0; i < objs.Count; i++)
if (!allowed.Contains(objs[i].ObjectId))
e.Remove(i);
};
ed.SelectionAdded += filter;
var selection = ed.GetSelection();
ed.SelectionAdded -= filter;
if (selection.Status == PromptStatus.OK)
return new TypedValue((int)LispDataType.SelectionSet, selection.Value);
else
return nil;
}
}
}
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