Use QML application in tray icon

qmlapp_trayicon.cpp

#include <QApplication>
#include <QQmlApplicationEngine>
#include <QMessageBox>
#include <QAction>
#include <QMenu>
#include <QSystemTrayIcon>

int init_trayicon_app() 
{
    if (!QSystemTrayIcon::isSystemTrayAvailable()) {
        QMessageBox::critical(0, QObject::tr("Systray"),
                                 QObject::tr("No systray was found."));
        return 1;
    }

    QApplication::setQuitOnLastWindowClosed(false);
    return 0;
}

void init_trayicon() 
{
    QObject *root = 0;
    if (engine.rootObjects().size() > 0)
    {
        root = engine.rootObjects().at(0);

        QAction *minimizeAction = new QAction(QObject::tr("Mi&nimize"), root);
        root->connect(minimizeAction, SIGNAL(triggered()), root, SLOT(hide()));
        QAction *maximizeAction = new QAction(QObject::tr("Ma&ximize"), root);
        root->connect(maximizeAction, SIGNAL(triggered()), root, SLOT(showMaximized()));
        QAction *restoreAction = new QAction(QObject::tr("&Restore"), root);
        root->connect(restoreAction, SIGNAL(triggered()), root, SLOT(showNormal()));
        QAction *quitAction = new QAction(QObject::tr("&Quit"), root);
        root->connect(quitAction, SIGNAL(triggered()), qApp, SLOT(quit()));

        QMenu *trayIconMenu = new QMenu();
        trayIconMenu->addAction(minimizeAction);
        trayIconMenu->addAction(maximizeAction);
        trayIconMenu->addAction(restoreAction);
        trayIconMenu->addSeparator();
        trayIconMenu->addAction(quitAction);

        QSystemTrayIcon *trayIcon = new QSystemTrayIcon(root);
        trayIcon->setContextMenu(trayIconMenu);
        trayIcon->setIcon(QIcon(":/trayicon.png"));
        trayIcon->show();
    }
}

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

    init_trayicon_app();
	
    QQmlApplicationEngine engine;
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));

    init_trayicon();

    return app.exec();
}

This will crash with Qt5.4