StartupObject property is not erased after enabling `Application Framework` property

Visual Studio Version: Int Preview 16.8.0 Preview 4.0 [30514.8.main]

Summary: If you disable the Application Framework and reenable it, the StartupObject in the vbproj file is not removed. This is specifically in VB Winforms applications.

Steps to Reproduce:

1. Open the VBWinforms.sln found in https://github.com/dotnet/winforms/tree/master/src/System.Windows.Forms/tests/IntegrationTests/VisualBasicTemplate.

2. With the properties pages and project file side to side, disable the Enable application framework property. StartupObject property should appear.

3. Reenable the Enable application framework property.

Expected Behavior: StartupObject property should be removed.

Actual Behavior: StartupObject property is not removed.

User Impact: If the user disables and then re-enables the Enable application framework property without any other change, the project is in a weird state and shows an error dialogue as shown.

cc: @KathleenDollard

[melytc]

https://github.com/dotnet/project-system/pull/8419 addresses this and ensures we have the correct values set in the project file and myapp file as described in the last comment.

[KlausLoeffelmann]

I am confused.

The Application Framework is on by default. We have something in the <StartupObject> (VbWinFormsFramework.My.MyApplication maybe? But I’d say it doesn’t really matter)

1. We disable the AppFramework. - Could we put the Form from application.myapp as StartObject?
2. We enable the AppFramework (We could put VbWinFormsFramework.My.MyApplication here, but probaby anything else would be find.)
3. We disable the AppFramework - again, we could put the Form from application.myapp as StartObject.

Would that work? Would it make sense?