CRASH: winId can return a bad handle if the widget was closed already

#include <QtWidgets>
#import <AppKit/AppKit.h>


class MyWidget : public QDialog
{
    bool event(QEvent *event) override
    {
        if (event->type() == QEvent::Show) {
            qDebug() << "fixTitleBar called: WinID" << winId();
            NSView* mainView = reinterpret_cast<NSView *>(winId());
            NSLog(@"mainView %@", mainView); //accessing the bad reference
        }
        return QDialog::event(event);
    }
};




int main(int argc, char **argv)
{
    QApplication app(argc, argv);
    MyWidget w;
    qDebug() << 1 << w.exec();
    qDebug() << 2 << w.exec();
    return 0;
}

    void closeEvent(QCloseEvent *e) override
    {
        e->ignore();
        hide();
    }