Converting code to new Qt5 syntax of connect

[vlada]

Hi,

here is a piece of my code:

QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
engine.load(QUrl(QStringLiteral("qrc:/qml/main.qml")));
QmltoCpp *qmltocpp = new QmltoCpp(); // my C++/QML interface
QObject *rootObject = engine.rootObjects().first();
QObject::connect(qmltocpp, SIGNAL(showMessage(QVariant)), rootObject, SLOT(showMessage(QVariant)));
return app.exec();

I would like to update this to the new Signal/Slot syntax. But I have no idea how.

This doesn't work:

QObject::connect(qmltocpp, &QmltoCpp::showMessage, rootObject, &QObject::showMessage);

Do I need to subclass a QObject and create new class for my rootObject? Would it help at all?

[raven-worx]

@vlada said in Converting code to new Qt5 syntax of connect:

QObject::connect(qmltocpp, &QmltoCpp::showMessage, rootObject, &QObject::showMessage);

it doesn't work because the QObject class doesn't have a method with the signature showMessage(QVariant)
You could cast the QObject to your class if you are sure that its of a certain type, if not it will crash.

So the code might look like this:

MyType* rootObject = qobject_cast<MyType*>(engine.rootObjects().first());
QObject::connect(qmltocpp, &QmltoCpp::showMessage, rootObject, &MyType::showMessage);

alternatively (but with actually no benefit to the "old" syntax):

MyType* rootObject = qobject_cast<MyType*>(engine.rootObjects().first());
QObject::connect(qmltocpp, &QmltoCpp::showMessage, [rootObject](const QVariant & v) {
     QMetaObject::invokeMethod( rootObject, "showMessage", Qt::DirectConnection, Q_ARG(QVariant,v) );
});