How can I start application in background, i.e. without showing GUI?

Question

I'm using Qt for taking screenshots (screen printing).

QPixmap::grabWindow(QApplication::desktop()->winId());

I'd like the application to start in background, i.e. I want it to be hidden when it starts (or even run in console mode).
How can I do that in Qt?

Answer 1

As I understand, you need an app that, when executed, doesn't show a widget (UI) and runs in the background.

One way to achieve this is to launch the app and show an icon in System tray instead of showing a dialog/window on the screen.

You can code this something like this:

// main.cpp

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

    // this is the important bit
    app.setQuitOnLastWindowClosed(false);
    
    // Say "Window" is your class which inherits QWidget or QDialog or QMainWindow
    Window window;
    // Don't call window.show()
    // Setup and invoke system tray icon in the constructor

    return app.exec();
}

There are a few other things you'd need to set. You can refer to the System Tray Icon Example for that.

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Update 2022:
If you are looking for a way to invoke the app using a global shortcut you might wanna look into options other than Qxt, as libqxt is no longer maintained and might not work with newer versions of Qt.