Prevent QApplication app from closing if a service is running

Question

I have a QML app in which I have subclassed QApplication to create my main screen with QML. The issue i have is on clicking Close button the application closes as intended, but I want to handle a situation where if some services are running I want to override close button behaviour.

I tried overriding closeEvent() without any luck. Can anyone point me to some ways I can handle this?

UPDATE : This is the code snippet I tried

class SingleApplication : public QApplication {
    Q_OBJECT
public:
    SingleApplication(int &argc, char **argv);

    void closeEvent ( QCloseEvent * event )
    {
        event->ignore();

    }
}

MAIN.cpp

#include "view.h"
#include <QDebug>
#include <QDesktopWidget>
#include "SingleApplication.h"

int main(int argc, char *argv[])
{
    SingleApplication app(argc, argv);
    if(!app.isRunning()) {

        app.processEvents();

        View view(QUrl("qrc:/qml/main.qml"));
#ifdef Q_OS_LINUX
        view.setFlags(Qt::WindowMinimizeButtonHint|Qt::WindowCloseButtonHint);
#endif
        view.setMaximumSize(QSize(1280,700));
        view.setMinimumSize(QSize(1280,700));

        // Centering the App to the middle of the screen
        int width = view.frameGeometry().width();
        int height = view.frameGeometry().height();
        QDesktopWidget wid;
        int screenWidth = wid.screen()->width();
        int screenHeight = wid.screen()->height();
        view.setGeometry((screenWidth/2)-(width/2),(screenHeight/2)-(height/2),width,height);


        view.show();

        return app.exec();
    }
    return 0;

}

Answer 1

There is no QApplication::closeEvent. Such virtual function belongs to QWidget.

Use of QApplication indicated that you have normal QWidget container for your QML UI (as you say UI is based on QML though). You should rather override that widget closeEvent e.g.:

class MyMainWidget : public QWidget // or is it QMainWindow?
{
   // snip
private:
    void closeEvent(QCloseEvent*);
}

void MyMainWidget::closeEvent(QCloseEvent* event)
{
    // decide whether or not the event accepted
    if (condition())
       event->accept();
}

And if your container widget is not overridden yet (simply QWidget?), well, now you have to do so.

And you did not say whether or not you want to keep app window running. I assume you want that as well.