Find screen a QWidget is located on

Question

With functions

QApplication::desktop()->screenCount();
QApplication::desktop()->screenGeometry();

I find how much screens exist on my system and on which screen coordinates they are located. Now I want to find out on which screen a QWidget is located at. How can I do that? Do I have to check the coordinates of the QWidget against the screen-coordinates or is there a more elegant way for this which returns the screen-number directly?

Answer 1

QDesktopWidget is deprecated in newer Qt versions (5.11 and above, not deprecated in 5.10).

Since Qt 5.10 there is QGuiApplication::screenAt(QPoint) as a replacement for screenNumber(QPoint).

Seems there is no direct replacement for screenNumber(QWidget*). However, it is possible to get information about the screen where the widget in question is located through QScreen pointer:

QScreen *screen = widget->window()->windowHandle()->screen();
qDebug() << screen->geometry()
                << screen->availableGeometry();

Answer 2

I think the function you should be looking for is this

int QDesktopWidget::screenNumber(const QPoint &point) const

This is an overloaded function. Returns the index of the screen that contains the point, or the screen which is the shortest distance from the point.

since i don't have multiple screens, you can check for yourself, the QWidget::pos() function provides the QPoint

Edit: As suggested by scopchanov in comments, you can also use

QDesktopWidget::screenNumber(const QWidget *widget = Q_NULLPTR)

Answer 3

In addition to Sillicomancers answer, I use the following code to replace the depricated QDesktopWidget::availableGeometry(const QWidget *widget)

QScreen* pScreen = QGuiApplication::screenAt(widget->mapToGlobal({widget->width()/2,0}));
QRect availableScreenSize = pScreen->availableGeometry();

which uses the screen where the middle of the top of widget is located.

Answer 4

QWidget::screen() introduced in Qt5.14.