Upgrading .NET Framework Add-In for Inventor 2026

[ppauleSHGR6]

Hi everyone,

I've just upgraded my C# Inventor Add-In, which was initially developed for Inventor 2023 for .NET Framework, to .NET 8.0 and I am facing a strange behaviour of Inventor 2026 when the Add-In was loaded.

The issue is, that Inventor 2026 fails to open any file as soon as the Add-In was loaded before.

When opening a file, a empty windows appears in the left top corner of the application window:

When I unload/uninstall my Add-In, restart Inventor 2026, open the same file again, everything works.

When debugging in VS22 there are no exceptions thrown and I can't find any suspicious things. The code is executed without problems.

I don't know how to continue from this point and how to find the cause for this issue, the only thing I know is, that it is somehow related to my Add-In.

Thanks for any assistance, very much appreciated!

[bradeneuropeArthur]

could you please share some more details about the addin and what it is doing?

[ppauleSHGR6]

Of course!

In general the Add-In opens a WPF dialog when saving a file, e.g. an IPT or IAM file and writes back into custom iProperties.

I'm attaching event handlers to the following events:

• ApplicationEvents.OnActivateDocument
• ApplicationEvents.OnSaveDocument

I already tried to comment these lines so only a config file gets read in the "Activate" method of the Add-In - but no success.

Plus in debug all code in the "Activate" method is executed without exceptions.

Here's the code of the "Activate" method:

public void Activate(Inventor.ApplicationAddInSite addInSiteObject, bool firstTime)
{
    try
    {
        AppSettings.Log.Info($"Loading AddIn... (Assembly={this.GetType().Assembly})");

        // Read reg keys
        // >>
        AppSettings.ServerPath = RegHandler.GetConfigPathFromReg();
        if (string.IsNullOrWhiteSpace(AppSettings.ServerPath))
            throw new Exception(@"Add-In could not be loaded. ServerPath is missing in Windows Registry");

        AppSettings.Log.Info($"ServerPath={AppSettings.ServerPath}");

        AppSettings.AssemblyFolder = System.IO.Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location);
        AppSettings.Log.Info($"AssemblyFolder={AppSettings.AssemblyFolder}");
        AppSettings.Log.Info($"LayoutFolder={AppSettings.LayoutDir}");

        AppSettings.ConfigFileName = System.IO.Path.Combine(AppSettings.ServerPath, AppSettings.ConfigFile);
        AppSettings.DbConfigFileName = System.IO.Path.Combine(AppSettings.ServerPath, AppSettings.DbConfigFile);
        AppSettings.UserConfigFileName = System.IO.Path.Combine(AppSettings.ServerPath, AppSettings.UserConfigFile);

        AppSettings.Log.Info($"ConfigFileName={AppSettings.ConfigFileName}");
        AppSettings.Log.Info($"DbConfigFileName={AppSettings.DbConfigFileName}");
        AppSettings.Log.Info($"UserConfigFileName={AppSettings.UserConfigFileName}");

        if (!Directory.Exists(AppSettings.LayoutDir))
            Directory.CreateDirectory(AppSettings.LayoutDir);

        if (!System.IO.File.Exists(AppSettings.ConfigFileName))
            throw new Exception($"File not found: {AppSettings.ConfigFileName}");

        if (!System.IO.File.Exists(AppSettings.DbConfigFileName))
            throw new Exception($"File not found: {AppSettings.DbConfigFileName}");

        if (!System.IO.File.Exists(AppSettings.UserConfigFileName))
            throw new Exception($"File not found: {AppSettings.UserConfigFileName}");
        // <<

        // Read config files
        // >>
        PropertyDialog.LoadConfig(AppSettings.ConfigFileName);
        PropertyDialog.LoadDbConfig(AppSettings.DbConfigFileName);
        PropertyDialog.GetAllowedUsers();
        // <<

        m_inventorApplication = addInSiteObject.Application;
        m_inventorApplication.ApplicationEvents.OnActivateDocument += ApplicationEvents_OnActivateDocument;
        m_inventorApplication.ApplicationEvents.OnSaveDocument += OnSaving;
		
        AppSettings.Log.Debug($"Event handlers attached");

        AppSettings.Log.Info("AddIn activated");
    }
    catch (Exception ex)
    {
        AppSettings.Log.Error(ex.Message);
        if (ex.InnerException != null)
            AppSettings.Log.Error(ex.InnerException.Message);
    }
}

This is a snippet of the VS project file:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>net8.0-windows</TargetFramework>
    <ProjectType>Local</ProjectType>
    <ApplicationIcon>favicon.ico</ApplicationIcon>
    <AssemblyKeyContainerName>
    </AssemblyKeyContainerName>
    <AssemblyOriginatorKeyFile>addinname.pfx</AssemblyOriginatorKeyFile>
    <DefaultClientScript>JScript</DefaultClientScript>
    <DefaultHTMLPageLayout>Grid</DefaultHTMLPageLayout>
    <DefaultTargetSchema>IE50</DefaultTargetSchema>
    <DelaySign>false</DelaySign>
    <OutputType>Library</OutputType>
    <RootNamespace>InvAddIn</RootNamespace>
    <RunPostBuildEvent>OnBuildSuccess</RunPostBuildEvent>
    <StartupObject>
    </StartupObject>
    <UseWPF>true</UseWPF>
    <ImportWindowsDesktopTargets>true</ImportWindowsDesktopTargets>
    <Configurations>Debug_23;Debug_24;Debug_26;Debug;Release_23;Release</Configurations>
    <AssemblyName>addinname</AssemblyName>
    <SignAssembly>true</SignAssembly>
  </PropertyGroup>
  <!-- ... -->
</Project>

These are the references I use for the Add-In:

I don't understand why there is popping up an empty dialog when the Add-In only is loaded and I try to open a file even if I don't attach the event handlers.

Plus the "" event handler doesn't do anything regarding dialogs:

private void ApplicationEvents_OnActivateDocument(_Document DocumentObject, EventTimingEnum BeforeOrAfter, NameValueMap Context, out HandlingCodeEnum HandlingCode)
{
    HandlingCode = HandlingCodeEnum.kEventNotHandled;

    if (BeforeOrAfter == EventTimingEnum.kAfter)
    {
        AppSettings.Log.Info($"ApplicationEvents_OnActivateDocument() DisplayName={DocumentObject.DisplayName}, FileName={DocumentObject.FullFileName}");

        m_openedDoc = DocumentObject;
        Savecounter = 0; // reset save counter

        HandlingCode = HandlingCodeEnum.kEventHandled;
    }
}

Any help is much appreciated.

[JelteDeJong]

When i went from 2023 to 2025 (.Net core) I noticed that Inventor is reacting differently to events. I can't say what is different, but I would have a look at the line

HandlingCode = HandlingCodeEnum.kEventHandled;

 in your "ApplicationEvents_OnActivateDocument" function. Try commenting it out as a test. 

If that does not work, you could try commenting out the line:

m_inventorApplication.ApplicationEvents.OnActivateDocument += ApplicationEvents_OnActivateDocument;

or 

m_inventorApplication.ApplicationEvents.OnSaveDocument += OnSaving;

in your "Activate(..)" function. Just as a test to see where the problem is coming from.

[ppauleSHGR6]

Thank you for your reply, unfortunately not attaching the event handlers does not lead to success.

That was indeed one of the first things I tried, as I mentioned in my initial post (... I already tried to comment these lines so only a config file gets read in the "Activate" method of the Add-In - but no success.)

I had the same assumption as this only happens when opening a file.

My next approach would probably be to create a new project and transfer the logic of the existing add-in piece by piece into the new project.

I didn't come up with any new findings yet.

Thanks for any advice.