Visual studio 2019 windows forms designer
As of version 16.8.0 Preview 2.1 I have found that I have to turn off this setting and restart and add my form. Once added, I can turn it back on, restart and work.
To enable the designer, download and install the Windows Forms .NET Core Designer VSIX package.
See article: https://devblogs.microsoft.com/dotnet/introducing-net-core-windows-forms-designer-preview-1/
I had the same problem. The following steps helped me
- Remove any other classes than the Form class in the yourformname.cs file
- Unload the project and right click on the project and choose edit project
- Make sure yourformname form has the SubType set to form
<SubType>Form</SubType>
and save the file - Reload the project