If you are using Qt Creator:
  • Open your project
  • Right click and select Add New...
  • Select Qt, Qt Designer Form Class, then Choose...
  • Select QWidget (or whatever) as the template
  • Provide file names and whether to save in a version control.
  • Build the new form
  • Done.


If you using Designer outside QtCreator:
  • Open Designer
  • Select QWidget or another template
  • Build the new form
  • Save the UI file and add it to your project's FORMS variable
  • Done.


See "Using Custom Widgets with Qt Designer" in Assistant for how to insert these new widgets into the QStackedwidget in the QMainWindow.