SharpDevelop Forms Designer not working in Revit 2021

[sragan]

In Revit 2020, I can create a new C# module, create a new C# Macro, go to Project, Add New Item, and add a WPF C# Window which is named Window1.

If I then select the Window1 I can view the code.  Clicking the "Design" tab at the bottom of the code window shows a preview of the window.

In Revit 2021, I get no preview.  Just an error message:

System.NullReferenceException: Object reference not set to an instance of an object.
at ICSharpCode.FormsDesigner.Services.TypeResolutionService..ctor()
at ICSharpCode.WpfDesign.AddIn.MyTypeFinder..ctor()
at ICSharpCode.WpfDesign.AddIn.MyTypeFinder.Create(OpenedFile file)
at ICSharpCode.WpfDesign.AddIn.WpfViewContent.LoadInternal(OpenedFile file, Stream stream)
at ICSharpCode.SharpDevelop.Gui.AbstractViewContentHandlingLoadErrors.Load(OpenedFile file, Stream stream)

Is there any fix?  

[Organon]

@H.echeva,

It works for me, but you have to do it every time you open Revit.

This problem only occurs from version 2021, so you can use version 2019/2020.

Regards,

[H.echeva]

Well, I think I found another (radical) solution.

I have copied the content of the folder SDA from 2018 to the folder in 2022.

The form works! I hope I haven't broken anything. I have kept a backup just in case.

[Organon]

@H.echeva,

That was a risky move. 😃👍

[sragan]

Oddly enough, the Forms Designer works again on a fresh install of Revit 2024.

Strange.

[rbustos]

I found a possible solution:
copy the SDA from Revit 2019 to Revit 2023