"window.external" evaluation in WebBrowser control gives error "Unexpected call to method or property access."

• .NET Core Version: .NET 5.0.101

• Have you experienced this same bug with .NET Framework?: No.

Problem description:

As of .NET 5.0, the “window.external” object reference that’s intended to provide access to the WebBrowser.ObjectForScripting property value does not work. It worked in .NET Core 3.1.

I didn’t find any information about this behavior in the .NET 5 documentation for Breaking Changes or Known Issues.

Evaluating “window.external” in the control’s browser environment produces the following error message:

“Unexpected call to method or property access.”

Here’s a screenshot of the error:

Expected behavior:

A “normal” message box should show (with the message “called from script code”).

Minimal repro:

https://github.com/rummelsworth/WebBrowserControlTutorial

The above-linked repo is an implementation of the WebBrowser control’s “2-way communication” tutorial. It has 3 branches:

• One branch targets netcoreapp3.1 and does not reproduce the error.
• The main branch targets net5.0 and reproduces the error.
• Another branch also targets net5.0 but has been migrated to use WebView2 instead of WebBrowser.

[rummelsworth]

@RussKie I think the links are visible above my previous comment in the GitHub UI but probably not included in the notification emails. Here are the links:

• dotnet/docs-desktop#169
• dotnet/docs#22365

Thanks again.

[RussKie]

I bisected it, and it looks like we regressed in #3388.

@weltkante looks like not all ComVisible attributes were incorrect after all.