How to create and use C++ objects in QML Javascript

Question

My app uses both c++ and QML.

I\'ve defined several objects in C++ part to access SQL etc.

It looks like:

Answer 1

Here is an example with an imagined TextFile class. First of all, we need a factory class as already suggested:

// Factory class
class Creator : public QObject
{
    Q_OBJECT
    public:
    Q_INVOKABLE QObject* createObject(const QString& typeName, const QVariantMap& arguments);
};

QObject* Creator::createObject(const QString& typeName, const QVariantMap& arguments)
{
    if (typeName == "TextFile")
    {
        QString filePath = arguments.value("filePath").toString();
        TextFile::OpenMode openMode =
                qvariant_cast(arguments.value("openMode", TextFile::ReadWrite));
        QString codec = arguments.value("codec", "UTF-8").toString();
        return new TextFile(qmlEngine(this), filePath, openMode, codec);
    }

    Q_ASSERT(false);
    return nullptr;
}

Note: This class is a bit more complicated than necessary. It is supposed to create multiple types. Now that we have the factory class in place, we need to tell the QML/QJSEngine what to do when calling the operator new for TextFile.

    QJSValue creator = engine.newQObject(new Creator());
    engine.globalObject().setProperty("_creator", creator);
    engine.evaluate("function TextFile(path, mode) { return _creator.createObject(\"TextFile\", { filePath: path, openMode: mode }); }");

Now we can instanciate our TextFile as desired, even with parameters:

var myFile = new TextFile("/path/to/file", TextFile.ReadWrite);

Credits go to the author of this answer.