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user3821746 February 2016

Instantiating QML object in existing C++ QT Project

We have an existing QT project written in C++, and we want to add something like the mapViewer example project to our existing UI. We can't figure out how to instantiate the mapViewer, and invoke the method that initializes/displays it. Following online help, we came up with the function below, that returns a QQuickWidget which we can add to a UI element. We keep getting an error that the created component never gets to be ready, so the function does not work.

QQuickWidget *buildMap(QWidget *parent)
    QQmlEngine *engine = new QQmlEngine;
    QQmlComponent component(engine, "qrc://mapviewer.qml");

    QObject *object = component.create();
    QMetaObject::invokeMethod(object, "initializeMap");

    QQuickWidget *map = new QQuickWidget(engine, parent);
    return map;

It does not make a ton of sense to us that we are creating an object using the mapViewer component, and then just forgetting about it, but the examples we found online have a flow similar to this.


ddriver February 2016

Try something like this instead:

QQuickWidget *buildMap(QWidget *parent) {
    QQuickWidget *map = new QQuickWidget(parent);
    return map;

As for the initializeMap method, maybe call it in mapviewer.qml's onCompleted? If you insist on calling it from C++, you can still get to the object thorugh map->rootObject()

Also, when creating components and objects, be that from C++ or QML, it is always a nice idea to check the status and output error strings if any, you don't just assume it will all work and then wonder why it doesn't.

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Asked in February 2016
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