Duplication of object in C++ and QML

twall

Hello, I'm working on an application that has both C++ and QML components. The application has a 'parsing' class that interprets data from another process. This data is sent from the parser to a different, but relevant class for processing, then displayed in the QML frontend. Right now I handle the passing of the data from the parser by having the data as a class member variable, which is further represented as a QML property. From there it is passed to a QML instance of the data processing class. Essentially, I perform my connect() call in QML when it could be done in C++.

This means that my parsing class has member variables of everything that comes in from the other process, as well as that data being a member variable of the relevant class. This essentially duplicates all of my data.

I would like to be able to connect the 'value received' signal from the parser to a slot in the relevant processing class, then have the processing class handle the QML properties of itself. However, I've been having trouble representing an object created in C++ represented in QML. I can create an object of that class in QML, and process that data in C++, but not the other way around.

Is there a way to have the same object be represented simultaneously in C++ and QML?

twall

AHA! In QML, wrap the QObject-derived classes that you made in an Item{} and findChild will find them just fine.

mrjj

Hi
Do you mean like the sample ?
http://doc.qt.io/qt-5/qtqml-cppintegration-contextproperties.html

class ApplicationData : public QObject
{
    Q_OBJECT
public:
    Q_INVOKABLE QDateTime getCurrentDateTime() const {
        return QDateTime::currentDateTime();
    }
};

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

    QQuickView view;

    ApplicationData data;
    view.rootContext()->setContextProperty("applicationData", &data);

    view.setSource(QUrl::fromLocalFile("MyItem.qml"));
    view.show();

    return app.exec();
}

twall

I've considered that, but I'd much rather have the property of the QML object be set by a signal from the parser, rather than by calling the parser directly.

mrjj

Ok, sounds like you already tried the doc stuff ?
https://doc-snapshots.qt.io/qt5-5.9/qtqml-cppintegration-interactqmlfromcpp.html
"Accessing Loaded QML Objects by Object Name"
Like find by name and since its a qobject, cant you just bind the c++ parsers
signal to a property in the object ?
I assume its some more complicated you want and Im afraid its outside my territory :)

Lets see what others suggest

twall

I have mostly tried the doc stuff, I'll keep with it and post any solutions I find

twall

So, I've found that I cannot view my QML object in C++ if the QML object's parent is not the root object. When I created the class, I left the default QObject inheritance as a nullptr, and that extended to when I created the object in QML.

twall

AHA! In QML, wrap the QObject-derived classes that you made in an Item{} and findChild will find them just fine.