如何从main.cpp获取qml中的activeFocusItem属性？

Question

I'm looking for a way to retrieve qml item properties which are not in type of base types in C++. I've found this:

QWindow *w = (QWindow *)engine.rootObjects().first();
QVariant p = w->property("color");

but the result is a instance of QVariant. I want to get properties like activeFocusItem .

Answer 1

Well, in fact you can get the value of activeFocusItem if you use the required toT() function for the QVariant .

In you case it should be something like

QQuickWindow *w = (QQuickWindow*) engine.rootObjects().first();
qDebug() << w->activeFocusItem()->property("activeFocus").toBool(); // true obviously
qDebug() << w->activeFocusItem()->property("objectName").toString();

In this code, we're getting the properties activeFocus and objectName , but it's just an example.

Another way,

QQuickWindow *w = (QQuickWindow*) engine.rootObjects().first();
QQuickItem *wi = w->property("activeFocusItem").value<QQuickItem*>();
qDebug() << wi->property("activeFocus").toBool();
qDebug() << wi->property("objectName").toString();

According to the documentation ,

Because C++ forbids unions from including types that have non-default constructors or destructors, most interesting Qt classes cannot be used in unions. Without QVariant, this would be a problem for QObject::property() and for database work, etc.

Usually, you interact with C++ using signals. In that case, when a QML object type is used as a signal parameter, the parameter should use var as the type, and the value should be received in C++ using the QVariant type. More info and examples here .

So QVariant is necessary and as I stated before the right way of getting QML objects to be used in C++.

I've uploaded a complete example to GitHub. I hope this may help you.