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I created a new WinForms project in Visual Studio 16.5.170.20430. The project is targeting DNC 3.1. I created a new user control in the root of the project named "Test" and received this error:

Value cannot be null. Parameter name: descriptor

I've done previous searches on the MSDN and SO and have turned up nothing relevant. I checked the designer file to see if there were any parameters or properties that seemed relevant. Couldn't find anything. Works fine in .NET 4.7.

Here's the call stack:

at Microsoft.VisualStudio.WinForms.RemoteClient.Proxies.ProxyManager.GetOrCreateObjectProxy(ObjectDescriptor descriptor) at Microsoft.VisualStudio.WinForms.RemoteClient.DesignerSession.InitializeRootComponent(CodeTypeDeclaration typeDeclaration, String resourceDocDataContent) at Microsoft.VisualStudio.WinForms.RemoteClient.Loader.RemoteCodeDomDesignerLoader.PerformLoad(IDesignerSerializationManager manager) at Microsoft.VisualStudio.Design.Serialization.CodeDom.VSCodeDomDesignerLoader.PerformLoad(IDesignerSerializationManager serializationManager) --- End of stack trace from previous location where exception was thrown --- at Microsoft.VisualStudio.Design.Serialization.CodeDom.VSCodeDomDesignerLoader.PerformLoad(IDesignerSerializationManager serializationManager) at Microsoft.VisualStudio.Design.Serialization.CodeDom.VSCodeDomDesignerLoader.DeferredLoadHandler.Microsoft.VisualStudio.TextManager.Interop.IVsTextBufferDataEvents.OnLoadCompleted(Int32 fReload)

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ernest
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  • regarding to [this post](https://devblogs.microsoft.com/dotnet/updates-to-net-core-windows-forms-designer-in-visual-studio-16-5-preview-1/), section *Features currently under development* - Designer support for UserControls and inherited forms and inherited UserControls is still under development. – Reza Aghaei Feb 03 '20 at 09:27
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    While the basic designer works well for some of the controls, but it's still not mature enough. You may still want to use [a workaround which was initially for older versions than 3.1](https://stackoverflow.com/a/53976235/3110834) for such features. – Reza Aghaei Feb 03 '20 at 09:32

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