topic Re: Rebar selected column in Revit API Forum

Rebar selected column

youssefGC — Sun, 01 Jan 2023 16:12:24 GMT

Hello forum.

I'm trying to code a program in order to rebar a selected column from the user using "Create From Curves", but i found a problem, when I execute the code an error message was shown :

"Référence d'objet n'est pas définie a une instance d'un objet"

The RebarBarType argument was extracted from a selected rebar

Source Code :

try { UIDocument uidoc = commandData.Application.ActiveUIDocument; Document doc = uidoc.Document; ; //select the column Reference reff = uidoc.Selection.PickObject(ObjectType.Element); ElementId idd = reff.ElementId; FamilyInstance P1 = doc.GetElement(idd) as FamilyInstance; //select the rebar Reference reff2 = uidoc.Selection.PickObject(ObjectType.Element); ElementId idd2 = reff2.ElementId; Rebar P2 = doc.GetElement(idd2) as Rebar; //get the rebar bar type RebarBarType RT = P2.Document.GetElement(P2.GetTypeId()) as RebarBarType; using (Transaction trns = new Transaction(doc,"Rebar")) { trns.Start(); LocationPoint location = P1.Location as LocationPoint; XYZ origin = location.Point; XYZ normal = new XYZ(1, 0, 0); XYZ rebarLineEnd = new XYZ(origin.X, origin.Y, origin.Z + 2); Line rebarLine = Line.CreateBound(origin, rebarLineEnd); IList<Curve> curves = new List<Curve>(); curves.Add(rebarLine); Rebar rebar = Rebar.CreateFromCurves(doc, Autodesk.Revit.DB.Structure.RebarStyle.Standard, RT, null, null, P1, normal, curves, RebarHookOrientation.Right, RebarHookOrientation.Left, true, true); trns.Commit(); } return Result.Succeeded; } catch (Exception ex) { message = ex.Message; TaskDialog.Show("error",message); return Result.Failed; }

But i can't locate the source of the problem

Thank you.

Re: Rebar selected column

jeremy_tammik — Sun, 01 Jan 2023 16:42:41 GMT

Happy New Year!

Before addressing your question, some advice on programming in general: I suggest you always clearly separate the UI from the calculation, and the calculation from the model modification. So:

Put the call to PickObject in its own separate exception handler (since an exception is thrown if the user cancels the selection)
Perform the calculation step to define the list of curves
Start the transaction and perform the rebar creation

Secondly, I would suggest adding a selection filter derived from the ISelectionFilter interface to your pick method:

https://www.revitapidocs.com/2023/d552f44b-221c-0ecd-d001-41a5099b2f9f.htm

That will guarantee that the selected object really is what you expect, and simplify the picking for the user.

Now, to address your question: maybe the user picked the wrong object. Maybe P@ or RT end up null. Debug through your code step by step interactively in the debugger and you will see which statement is causing the error. Then it will become obvious how it can be fixed.

Re: Rebar selected column

youssefGC — Tue, 03 Jan 2023 09:55:20 GMT

Thank you for the answer.

I try to use a selection filter of selection. And to make sure, I put a message box if the Rebar Type found or not.

but the same error.

try { UIDocument uidoc = commandData.Application.ActiveUIDocument; Document doc = uidoc.Document; ; RebarBarType RT = null; Reference reff = uidoc.Selection.PickObject(ObjectType.Element); ElementId idd = reff.ElementId; FamilyInstance P1 = doc.GetElement(idd) as FamilyInstance; var all_rebar_types =new FilteredElementCollector(doc) .OfCategory(BuiltInCategory.OST_Rebar).WhereElementIsElementType() .ToElements(); foreach (var rebar_type in all_rebar_types) { string rebar_name = rebar_type.get_Parameter(BuiltInParameter.SYMBOL_NAME_PARAM).AsString(); if (rebar_name == "01") { RT = rebar_type as RebarBarType; TaskDialog.Show("Message", "01 Exist"); break; } } using (Transaction trns = new Transaction(doc,"Rebar")) { trns.Start(); LocationPoint location = P1.Location as LocationPoint; XYZ origin = location.Point; XYZ normal = new XYZ(1, 0, 0); XYZ rebarLineEnd = new XYZ(origin.X, origin.Y, origin.Z + 2); Line rebarLine = Line.CreateBound(origin, rebarLineEnd); IList<Curve> curves = new List<Curve>(); curves.Add(rebarLine); Rebar rebar = Rebar.CreateFromCurves(doc, Autodesk.Revit.DB.Structure.RebarStyle.Standard, RT, null, null, P1, normal, curves, RebarHookOrientation.Right, RebarHookOrientation.Left, true, true); trns.Commit(); } return Result.Succeeded; } catch (Exception ex) { message = ex.Message; TaskDialog.Show("error",message); return Result.Failed; }

Re: Rebar selected column

jeremy_tammik — Tue, 03 Jan 2023 10:23:31 GMT

Oh dear, how sad. Happy New Year anyway!

I searched The Building Coder for CreateFromCurves and found:

The first links to a blog post by Aaron Lu. That and the other article explain the details of using the method and provide several examples of doing so. I hope that helps you further.

Re: Rebar selected column

mhannonQ65N2 — Wed, 04 Jan 2023 16:39:25 GMT

Is the column Slanted? The cast on line 31 will return null for slanted columns, causing an error on line 32. Can you find which line the error is on?

Re: Rebar selected column

youssefGC — Thu, 05 Jan 2023 09:23:10 GMT

In my case, I didn't find any problem in selection, but the source of the problem is the variable RT (RebarBarType).

Till today, i can't locate the problem exactly !

Re: Rebar selected column

jeremy_tammik — Thu, 05 Jan 2023 11:56:03 GMT

Can you step through and debug?

Re: Rebar selected column

manhgt214 — Sun, 17 Aug 2025 10:15:39 GMT

You can get RebarType by using LINQ

var mainBarType = new FilteredElementCollector(doc) .OfClass(typeof(RebarBarType)).Cast<RebarBarType>() .FirstOrDefault(bt => bt.Name == "32M");

refer video create Rebar of Column:
https://youtu.be/Sxdq36EreA4?si=I_m2fuN7-qxTjqI_