How to retrieve laptop's 'Display resolution'?

Bart_Vandewoestyne

I'm a bit confused... Using Qt 5.15.1, I would like to retrieve the "Display resolution" of my laptop (no external screens attached), as given in Windows 10 as follows:

Since according to https://doc.qt.io/qt-5/qdesktopwidget.html the QDesktopWidget class is obsolete, I want to avoid using that, so I tried using QScreen in the following way:

const auto screens = QApplication::screens();
for (const auto& screen : screens)
{
    const auto geometry = screen->geometry();
    const auto width = geometry.width();
    const auto height = geometry.height();
}

However, when I try this, it appears that screens has size 0, so no screens are found...

Am I on the right track to retrieve my Display resolution, or am I doing stuff completely wrong and should I use something else than QScreen?

jsulm

@Bart_Vandewoestyne said in How to retrieve laptop's 'Display resolution'?:

it appears

it appears or did you check it is really 0? Because inside the loop you're defining local variables without doing anything with them.

J.Hilk

@Bart_Vandewoestyne works perfectly fine for me, it it is even from inside a VM

Bart_Vandewoestyne

@jsulm said in How to retrieve laptop's 'Display resolution'?:

it appears or did you check it is really 0? Because inside the loop you're defining local variables without doing anything with them.

I did check it as part of a larger application and it was really 0. However, I now also tried the following trimmed down minimal example:

#include <QApplication>
#include <QScreen>
#include <QDebug>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    const auto screens = QApplication::screens();
    qDebug() << screens.size();
    for (const auto& screen : screens)
    {
        const auto geometry = screen->geometry();
        const auto screenName = screen->name();
        const auto width = geometry.width();
        const auto height = geometry.height();
        qDebug() << width << height;
    }
}

and .pro file

TEMPLATE = app
TARGET = qscreen
INCLUDEPATH += .

QT += widgets
CONFIG += console 

SOURCES += qscreen.cpp

and that works. So I'll now have to figure out what differences there are between this trimmed down program and my larger application. Stay tuned! I'll report back later! :-)

Bart_Vandewoestyne

@Bart_Vandewoestyne said in How to retrieve laptop's 'Display resolution'?:

So I'll now have to figure out what differences there are between this trimmed down program and my larger application. Stay tuned! I'll report back later! :-)

I'm a bit confused... as I now have:

A trimmed down stand-alone example program that works.
A unit test using the Google Test framework that I got working after creating a new Google Test main() function with
```
QApplication a(argc, argv);
```
right before
```
return RUN_ALL_TESTS();
```
In my larger application, I have main thread where, the first statement in my main() function is
```
QCoreApplication app(argc, argv);
```
Next to the main thread, I have another thread with an event loop, and it is in that thread that I'm trying to fetch the screen info, but it fails.

Any idea what could be wrong here? I'm quite in the dark, since I do call the QCoreApplication constructor in the beginning of my program, and the second thread does have an event loop (although I'm not sure if that is relevant for fetching the screen info)...

Chris Kawa

@Bart_Vandewoestyne said in How to retrieve laptop's 'Display resolution'?:

I'm quite in the dark, since I do call the QCoreApplication constructor in the beginning of my program

QCoreApplication is the base class for non-UI applications.
For UI stuff (desktop included) you need at least QGuiApplication or QApplication for widget based app.

Bart_Vandewoestyne

@Chris-Kawa said in How to retrieve laptop's 'Display resolution'?:

QCoreApplication is the base class for non-UI applications.
For UI stuff (desktop included) you need at least QGuiApplication or QApplication for widget based app.

I indeed overlooked that one. After switching from QCoreApplicatio to QGuiApplication everything works as expected and my screen is detected.

Thanks!