I tried it and it works correctly!
First I created two Forms in VS, named the first "BaseForm", the second "SubForm".
Then I put two Buttons and a Label on the BaseForm.
After that I opened the code-editor for SubForm.cs and modified the code from
- public partial class SubForm { ...
to
- public partial class SubForm : BaseForm { ...
to set the SubForm inherited from BaseForm.
Then compile, maybe close the designer windows/tabs and reopen them and I see the controls of BaseForm in designer mode of SubForm with an inheritance-indicator-symbol in the upper left of each inherited control.