Ask confirmation before closing a QQuickView or QApplication

Question

I am trying to catch a close event either in my MyApplication instance inheriting from QApplication or in my WindowQML instance inheriting from QQuickView. The goal is to ask confirmation to quit before really closing the application.

Before my application was relying on QMainWindow where I implemented the closeEvent() method like this:

// MainWindow inherits from QMainWindow
void MainWindow::closeEvent(QCloseEvent *event)
{
  event->ignore();
  confirmQuit(); // ask for confirmation first
}

The problem is that my class WindowQML which inherits from QQuickView never pass inside the closeEvent() method. I then tried to overload the event() method like this:

// WindowQML inherits from QQuickView
bool WindowQML::event(QEvent *event)
{
  if(event->type() == QEvent::Close)
  {
    qDebug() << "CLOSE EVENT IN QML WINDOW";
  }
}

but this event never happened either.

The next road I tried to take was to catch the close event in MyApplication like this:

// We need to check for the quit event to ask confirmation in the QML view
bool MyApplication::event(QEvent *event)
{
  bool handled = false;

  switch (event->type())
  {
    case QEvent::Close:
      qDebug() << "Close event received";
      event->ignore(); // mandatory?
      handled = true;
      Q_EMIT quitSignalReceived();
      break;

    default:
    qDebug() << "Default event received";
      handled = QApplication::event(event);
      break;
  }

    qDebug() << "Event handled set to : " << handled;
  return handled;
}

The signal quitSignalReceived() is emitted properly but the event is not "blocked" properly and my application still closes.

So I have two questions:

1. Is there a way to detect the closing event of a QQuickView instance?
2. If it is not possible, is the MyApplication::event() way the best course of action? Why do I need to call event->ignore() here? I would have thought that returning true would be enough.

Answer 1

I don't know why QWindow hasn't a closeEvent convenience event handler. Looks like a mistake, and sadly it can't be added before Qt 6.0. Anyhow, any QWindow definitely gets a QCloseEvent when it gets closed. So just override event and perform your event handling there.

Proofs:

1. QGuiApplication source code

2. this test program:

   #include <QtGui>
   
   class Window : public QWindow
   {
   protected:
       bool event(QEvent *e) Q_DECL_OVERRIDE
       {
           int type = e->type();
           qDebug() << "Got an event of type" << type;
           if (type == QEvent::Close)
               qDebug() << "... and it was a close event!";
   
           return QWindow::event(e);
       }
   };
   
   int main(int argc, char **argv) 
   {
       QGuiApplication app(argc, argv);
       Window w;
       w.create();
       w.show();
       return app.exec();
   }
   

   prints this

   Got an event of type 17 
   Got an event of type 14 
   Got an event of type 13 
   Got an event of type 105 
   Got an event of type 13 
   Got an event of type 206 
   Got an event of type 206 
   Got an event of type 8 
   Got an event of type 207 
   Got an event of type 19 
   ... and it was a close event! 
   Got an event of type 18