Are the types of objects you need to query for limited to Lines?
If yes, then I still see a problem with the solutions posted here, which is that they all presume that there can only be a single object passing through the query point. How can that be? Is there an assumption that no lines in the drawings you're working with intersect one another?
In any case, something I've always strived to do, is to avoid writing specific solutions to generic problems like this one. For example, the code below will operate on any type of Curve, but can also be constrained to operate on only a specific subtype using a generic argument. If you pass Line as the generic argument type, it should do exactly what @_gile 's example does (except that it will find all objects passing though the point, rather than just the first one it finds). You can pass any type derived from Curve as the generic argument (or Spline, Polyline, etc.), and it will look at and return those types. Passing Curve will look at and return any type of Curve, as is done in the example.
I wrote it to find all objects that pass through the point, because if you ask me, finding only the first object in a block that passes through a point is like playing spin-the-bottle. Try drawing a few intersecting curves, running the example command, and selecting the point where the curves intersect, and it should select both of them
public static class MyExtensions
{
/// <summary>
/// Returns a sequence of Curve-based types that pass
/// though the given point. The generic argument can
/// be Curve or any type derived from it, to constrain
/// the search and the result to only the specified type.
///
/// This method is not dependent on the drawing editor,
/// but the example that follows is.
/// </summary>
public static IEnumerable<T> GetCurvesAt<T>(
this IEnumerable<ObjectId> candidates,
Point3d point,
Transaction tr) where T: Curve
{
RXClass rxclass = RXObject.GetClass(typeof(T));
foreach(ObjectId id in candidates)
{
if(id.ObjectClass.IsDerivedFrom(rxclass))
{
T curve = (T)tr.GetObject(id, OpenMode.ForRead);
Curve3d curve3d = curve.TryGetCurve3d();
if(curve3d != null && curve3d.IsOn(point))
yield return curve;
}
}
}
public static Curve3d TryGetCurve3d(this Curve curve)
{
try
{
return curve.GetGeCurve();
}
catch(Autodesk.AutoCAD.Runtime.Exception)
{
return null;
}
}
}
public static class Example
{
[CommandMethod("SELECTCURVESATPOINT", CommandFlags.Redraw)]
public static void SelectCurvesAtPoint()
{
Document doc = Application.DocumentManager.MdiActiveDocument;
Editor ed = doc.Editor;
using(var tr = doc.TransactionManager.StartTransaction())
{
try
{
var ppr = ed.GetPoint("\nPick a point: ");
if(ppr.Status != PromptStatus.OK)
return;
Point3d pickpt = ppr.Value;
short pickbox = (short)Application.GetSystemVariable("PICKBOX");
double offset = (PixelSize * pickbox) / 2.0;
Vector3d delta = new Vector3d(offset, offset, offset);
PromptSelectionOptions pso = new PromptSelectionOptions();
pso.RejectObjectsFromNonCurrentSpace = true;
/// Use a selection filter to limit the selection
/// to specific type(s) of objects. This example
/// looks at all objects:
var psr = ed.SelectCrossingWindow(pickpt - delta, pickpt + delta);
if(psr.Status == PromptStatus.OK && psr.Value.Count > 0)
{
var ids = psr.Value.GetObjectIds().Cast<ObjectId>();
var curves = ids.GetCurvesAt<Curve>(pickpt, tr);
if(curves.Any())
{
var array = curves.Select(crv => crv.ObjectId).ToArray();
ed.SetImpliedSelection(array);
ed.WriteMessage($"\nFound {array.Length} object(s) at selected point.");
return;
}
}
ed.WriteMessage("\nNothing found at selected point. ");
}
finally
{
tr.Commit();
}
}
}
static double PixelSize
{
get
{
double vh = (double)Application.GetSystemVariable("VIEWSIZE");
Point2d pt = (Point2d)Application.GetSystemVariable("SCREENSIZE");
return vh / pt.Y;
}
}
}
