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

[tiagofrbr]

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-ex...

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());
            }
        }
    }
}

[scgq425]

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?

[tiagofrbr]

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);

[reylorente1]

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;
}

[scgq425]

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  

[tiagofrbr]

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; }
}