When may use QMainWindow instead of QDialog ?

[AndrzejB]

Example BasicLayouts uses QDialog. This dialog is main application window.
If I change QDIalog to QMainWindow, all widgets are invisible.
When is better using QMainWindow over QDialog?

[JonB]

@AndrzejB said in When may use QMainWindow instead of QDialog ?:

When is better using QMainWindow over QDialog?

Neither is "better", it spends what you facilities you want. QDialog is plain, QMainWindow has a number of "areas" reserved on it for menus, toolbars etc. as per the diagram at https://doc.qt.io/qt-5/qmainwindow.html#details. If you do not want any of those QMainWindow is overkill.

If I change QDIalog to QMainWindow, all widgets are invisible.

Then your code is wrong. For a QMainWindow as per Creating Main Window Components you must use

Note: Creating a main window without a central widget is not supported. You must have a central widget even if it is just a placeholder.
You set the central widget with setCentralWidget().

[AndrzejB]

setCentralWidget must be pointer or object?
Two situations:

• pointer: setCentralWidget(edit);
• object: setCentralWidget(&edit);

Object is deleted when mainform is deleted by C++.
object pointed by pointer is deleted by Qt library when mainform is deleted? What about place address object, not pointer?

[JonB]

@AndrzejB said in When may use QMainWindow instead of QDialog ?:

pointer: setCentralWidget(edit);

new => simple, safe.

object: setCentralWidget(&edit);

Usually OK, because edit variable goes out of scope and so is de-parented from QMainWindow before that gets destroyed.

I prefer new. Note that situation is no different for setCentralWidget() than any other time you place a widget on a widget, nothing special.

[mpergand]

@JonB said in When may use QMainWindow instead of QDialog ?:

Usually OK, because edit variable goes out of scope and so is de-parented from QMainWindow before that gets destroyed.

If QMainWindow is set with WA_DeleteOnClose it will clash for sure when the window is closed.