使用 Qt C++ 截屏

Question

I'm trying to take a screenshot with my application. But I get the following error message :

QPixmap: Must construct a QGuiApplication before a QPixmap

My program runs in the background and I do not want a GUI. How would I create a "QGuiApplication" and then hide the window permanently ? Or is there another way to take a screenshot without having to create a GUI ?

I was using the following code to take the screenshot :

QScreen *screen;
QPixmap qpx_pixmap;

screen = QGuiApplication::primaryScreen();
qpx_pixmap = screen->grabWindow(0);
screenshotTarget = dir.path() + "/" + QDateTime::currentDateTime().toString("dddd hh:mm:ss");
qpx_pixmap.save(screenshotTarget);

Answer 1

Create an instance of QGuiApplication on startup, before you create your QPixmap . You don't need to also create a GUI. QGuiApplication itself will not create any windows or anything visible.

A good place for that is at the start of main() :

int main(int argc, char* argv[])
{
    QGuiApplication app(argc, argv);

    // ...

It also works with QApplication , since it inherits from QGuiApplication . It just provides extra things needed for creating QWidget based objects, which you don't need. The important thing is that the QGuiApplication object is created before the QPixmap .

Finally, you need tell grabWindow() which part to grab. To grab the whole screen, use:

auto geom = screen->geometry();
qpx_pixmap = screen->grabWindow(0, geom.x(), geom.y(), geom.width(), geom.height());