topic ComboBox and Modeless Form - Getting error (Object reference not set...) in Revit API Forum

ComboBox and Modeless Form - Getting error (Object reference not set...)

tiagofrbr — Sun, 01 Dec 2024 01:02:00 GMT

Hi!
I've seen the post about this topic in the links below:
https://forums.autodesk.com/t5/revit-api-forum/modeless-form-and-combobox/td-p/9119051.
https://forums.autodesk.com/t5/revit-api-forum/how-to-retrieve-modeless-form-s-combobox-s-text-in-externalevent/m-p/10315511#M55898

However I couldn't figure it out in my code how to get data into my combobox, getting the same error: "Object reference not set to an instance of an object".

Hope someone can help me...

Command.cs

namespace ElectricalDiagrams { [Transaction(TransactionMode.Manual)] public class Command : IExternalCommand { public virtual Result Execute(ExternalCommandData commandData, ref string message, ElementSet elements) { UIApplication uiapp = commandData.Application; try { App.thisApp.ShowForm(uiapp); return Result.Succeeded; } catch(Exception ex) { message = ex.Message; return Result.Failed; } } } }

App.cs

namespace ElectricalDiagrams { public class App : IExternalApplication { internal static App thisApp = new App(); private ModelessForm form; public Result OnStartup(UIControlledApplication application) { form = null; thisApp = this; return Result.Succeeded; } public Result OnShutdown(UIControlledApplication application) { if (form != null && form.Visible) { form.Close(); } return Result.Succeeded; } public void ShowForm(UIApplication uiapp) { if (form == null || form.IsDisposed) { RequestHandler handler = new RequestHandler(); ExternalEvent exEvent = ExternalEvent.Create(handler); form = new ModelessForm(exEvent, handler); form.Show(); } } public void WakeFormUp() { if (form != null) { form.EnableCommands(true); } } } }

RequestHandler.cs

namespace ElectricalDiagrams { public class RequestHandler : IExternalEventHandler { private Request request = new Request(); public Request Request { get { return request; } } public string GetName() { return "External Event"; } public void Execute(UIApplication uiapp) { try { switch (Request.Take()) { case RequestId.None: { return; } case RequestId.GetPanels: { new GetPanels(uiapp, PanelComboBox); break; } default: { break; } } } finally { App.thisApp.WakeFormUp(); } return; } } }

Request.cs

namespace ElectricalDiagrams { public enum RequestId : int { None = 0, GetPanels = 1 } public class Request { private int request = (int)RequestId.None; public RequestId Take() { return (RequestId)Interlocked.Exchange(ref request, (int)RequestId.None); } public void Make(RequestId requestId) { Interlocked.Exchange(ref request, (int)requestId); } } }

ModelessForm.cs

namespace ElectricalDiagrams { public partial class ModelessForm : Form { //private Document doc; private RequestHandler requestHandler; private ExternalEvent externalEvent; public ModelessForm(ExternalEvent exEvent, RequestHandler handler) { InitializeComponent(); requestHandler = handler; externalEvent = exEvent; } protected override void OnFormClosed(FormClosedEventArgs e) { externalEvent.Dispose(); externalEvent = null; requestHandler = null; base.OnFormClosed(e); } public void EnableCommands(bool status) { foreach (Control control in this.Controls) { control.Enabled = status; } if (!status) { this.CancelButton.Enabled = true; } } private void MakeRequest(RequestId requestId) { requestHandler.Request.Make(requestId); externalEvent.Raise(); EnableCommands(false); } private void ModelessForm_Load(object sender, EventArgs e) { MakeRequest(RequestId.GetPanels); } private void CancelButton_Click(object sender, EventArgs e) { Close(); } } }

GetPanels.cs

namespace ElectricalDiagrams.Extensions { class GetPanels { public GetPanels(UIApplication uiapp, System.Windows.Forms.ComboBox PanelComboBox) { UIDocument uidoc = uiapp.ActiveUIDocument; Document doc = uidoc.Document; IList<Element> panelElements = new FilteredElementCollector(doc). OfCategory(BuiltInCategory.OST_ElectricalEquipment). WhereElementIsNotElementType(). ToElements(); List<string> panelNames = new List<string> (panelElements.Select<Element, string>(e => e.Name.ToString())); try { PanelComboBox.DataSource = panelNames; } catch (Exception ex) { TaskDialog.Show("Error", ex.ToString()); } } } }

回复： ComboBox and Modeless Form - Getting error (Object reference not set...)

scgq425 — Tue, 03 Dec 2024 07:30:37 GMT

Hi @tiagofrbr ：

are you debug this code ? and which row post this error?

this code logic like run the command and collected electraic data to combobox?

回复： ComboBox and Modeless Form - Getting error (Object reference not set...)

tiagofrbr — Mon, 09 Dec 2024 15:10:34 GMT

Yes I did. The row which posts this error is the row 24 from RequestHanlder.cs. The code logic was able to collect the electric data into the combobox, but I found that the issue is that the code at the row 24 from RequestHandler couldn't find the reference for "PanelComboBox", which is the combobox I created in my Modeless Form.

new GetPanels(uiapp, PanelComboBox);

Re: ComboBox and Modeless Form - Getting error (Object reference not set...)

reylorente1 — Mon, 09 Dec 2024 21:16:21 GMT

I've been checking your code, I don't master the electrical part of Revit. Add this part to the code, see if it works

public void Execute(UIApplication uiapp) { try { switch (Request.Take()) { case RequestId.None: { return; } case RequestId.GetPanels: var form = Application.OpenForms.OfType<ModelessForm>().FirstOrDefault(); if (form != null) { // Llama a la función para llenar el ComboBox form.Invoke((MethodInvoker)delegate { new GetPanels(uiapp, form.PanelComboBox); }); } break; default: { break; } } } finally { App.thisApp.WakeFormUp(); } return; }

回复： ComboBox and Modeless Form - Getting error (Object reference not set...)

scgq425 — Tue, 10 Dec 2024 02:02:17 GMT

Hi @tiagofrbr :

i test you code is run ok, i get all electric data and post to combobox . but in you code , i add this paramater to trans PanelCombobox .

and in the link file i push the project you can re-build and debug this .

public class Value { public static System.Windows.Forms.ComboBox PanelComboBox; }

public ModelessForm(ExternalEvent exEvent, RequestHandler handler) { InitializeComponent(); requestHandler = handler; externalEvent = exEvent; Value.PanelComboBox = this.PanelComboBox; }

. i push

Re: ComboBox and Modeless Form - Getting error (Object reference not set...)

tiagofrbr — Wed, 11 Dec 2024 18:29:44 GMT

Thanks for your help! Here's the solution that I found to be working:

public ModelessForm(ExternalEvent exEvent, RequestHandler handler, UIApplication Uiapp) { InitializeComponent(); requestHandler = handler; externalEvent = exEvent; uiapp = Uiapp; requestHandler.GetPanelComboBox = PanelComboBox; }

public class RequestHandler : IExternalEventHandler { public ComboBox GetPanelComboBox { get; set; } }