Layouts

is it possible to change the object name of the layouts and spacers in designer?
is it possible to apply stacked layouts with designer?

1. No.
2. Yes. Simply use a "Stacked Widget" as offered in the widget box. Or didn't I understand your question?

I wanted to use the QStackedLayout class in desinger?

what is the difference between stackedlayout and stacked widget

The latter is a QWidget containing a stacked layout.