Subclassing (promoting) non-QWidget in Designer
We've been using Qt Designer. It's likely we will want to subclass QLayout to do some specialized layout (hiding child widgets). I don't see a way to do this in Designer.
Also, we may want to have a custom spacer, that has the right size on either Mac or Windows. Is that possible as well?
(It's easy to promote a QWidget, but these guys aren't QWidgets.)
There is no way to subclass a QLayout in designer. You need real code for that.