Qt Designer: Changing the base class of a window

Question

I already created a second window for my application in the Qt Designer. I read that a QMainWindow would be the wrong class for the second window (which basically should only be some kind of dialog), so I would like to change the base class.

My Question(s) are:

1. Is there a way to change the base class without creating a new window and copying my code into the new files?
2. Can somebody please explain when to use QMainWindow, QDialog and QWidget? I did not found good explanations for the differences between these three base classes in Qt.

Answer 1

1. To change the base class you could only change the : public QMainWindow to : public QWidget (or vice-versa) in the header-file and of course also the *.cpp.

2. Basically all three are QWidgets, each with special functionality or for specific purposes. As far as I know the QMainWindow has toolbars, menubars and docks, a QDialog will always be shown as a seperate window (e.g. blocking, non-blocking, etc.) and the QWidget itself is the base-class. I.e. QPushButton, QCombobox are derived from QWidget too. In my opinion it would be better to use only one QMainWindow since it should be a central point of interaction/navigation for the user

EDIT: I forgot to mention that also the UI-file has to be changed, i.e. by using a text-editor, change the line (4th row I think)

<widget class="QMainWindow" name="YourClassName"> 

to

<widget class="QWidget" name"YourClassName"> 

and remove all QMainWindows related parts (menubar, toolbar, ...), and the enclosing tag for the central widget.

Thanks to alexisdm for the tip.