How to determine desktop number?!?

[Szyk]

Hi!
I am writing text editor in multiplatform way. In the past I most time spending on Windows, but now I am back to the Linux and I want next version of my text editor will be usable on Linux also.
Now am working with Kubuntu 18.10 with Kde Plasma windows manager. I have 4 virtual desktops. Most of the time I am working only with first of them. But I can image to work with file manager on some other screen and I want to run my editor from file manager many times (intense working with source files in many languages). I do some basic tests and I am failed to find "right Qt way" to determine number of desktop on which my text editor is running. I try:
1. Identify by screen pointer:

MainWindow w;
reinterpret_cast<quint64>(w.windowHandle()->screen()

MainWindow w;
reinterpret_cast<quint64>(w.windowHandle()->screen()

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Which is wrong because it is unique from instance to instance.
2. Find siblings of current screen:

QList<QScreen*> lScreens(w.windowHandle()->screen()->virtualSiblings());
for(QScreen* lScreen : lScreens)
    qInfo() << "Detected screen: " << reinterpret_cast<quint64>(lScreen);

QList<QScreen*> lScreens(w.windowHandle()->screen()->virtualSiblings());
for(QScreen* lScreen : lScreens)
    qInfo() << "Detected screen: " << reinterpret_cast<quint64>(lScreen);

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But it return only first screen (3 rest are ignored).
3. Identify by primaryScreen pointer:

qInfo() << "Detected screen: " << reinterpret_cast<quint64>(a.primaryScreen());

qInfo() << "Detected screen: " << reinterpret_cast<quint64>(a.primaryScreen());

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But it failed also (it is unique from instance to instance).
4. QDesktopWidget::screenNumber()
But it always return 0 (no mater what is current desktop).

Do you have any other ideas?

[tuli]

Did you pass your text editors widget to QDesktopWidget::screenNumber(QWidget*) ? Show some code.