Qt DBus unmarshalling when sent as QDBusVariant / QVariant

Question

Class Dummy, derived from QObject, registered

Q_DECLARE_METATYPE(Dummy)
qRegisterMetaType<Dummy>("Dummy");
qDBusRegisterMetaType<Dummy>();

When I send Dummy as QDBusVariant, the slot is correctly called, but the value (of Dummy) is default. Have noticed that the unmarshalling operator is never called (marshalling is). Via DBusMonitor I can see the value is sent correclty.

I assume it fails because the operator QDBusArgument &operator<<(const QDBusVariant &arg); is called and works only against Qt standard types. If I wrap a QString in QVariant in QDBusVariant it works fine.

How can solve the issue?

/*!
 * \brief operator << Marshalling
 * \param argument
 * \param dummy
 * \return
 */
QDBusArgument &operator<<(QDBusArgument &argument, const Dummy& dummy)
{
    argument.beginStructure();
    argument << dummy.m_number; // qint32
    argument << dummy.m_string; // QString
    argument.endStructure();
    qDebug() << "Marshall to DBus" << dummy.m_number << dummy.m_string;
    return argument;
}

/*!
 * \brief operator >> unmarshalling
 * \param argument
 * \param dummy
 * \return
 */
const QDBusArgument &operator>>(const QDBusArgument &argument, Dummy &dummy)
{
    argument.beginStructure();
    argument >> dummy.m_number;
    argument >> dummy.m_string;
    argument.endStructure();
    qDebug() << "Unmarshall from DBus" << dummy.m_number << dummy.m_string;
    return argument;
}

Sending:

        Dummy dummy(c++, "Moep");
        qDebug() << "Dummy is" << dummy;
        QVariant qv;
        qv.setValue(dummy);
        QDBusVariant qdv = QDBusVariant(qv);
        testserviceInterface.receiveVariant(qdv);

Remarks:

1. Qt 5.1 Win32
2. This here describes a similar issue with no answer as of posting date: Qt QDbus Sending Custom Types with QVariant

Answer 1

The trick is, that the received QVariant for complex types is of type QDBusArgument. If it is possible to unmarshall to the desired target type, then the way to do it, is: qv.value<QDBusArgument>() >> someConcreteObject