How I show application when open application again Qt

Question

Now, I have 1 application, but I don\'t want to open application twice, so I using QShareMemory to detect application when open twice. And my question is: how I

Answer 1

Just use QSingleApplication class instead of QApplication: https://github.com/qtproject/qt-solutions/tree/master/qtsingleapplication

int main(int argc, char **argv)
{
    QtSingleApplication app(argc, argv);
    if (app.isRunning())
        return 0;

    MyMainWidget mmw;
    app.setActivationWindow(&mmw);
    mmw.show();

    return app.exec();
}

It is part of Qt Solutions: https://github.com/qtproject/qt-solutions