Qt QDbus Sending Custom Types with QVariant

问题

I'm trying to send a custom class ( "Span" ) inside a QVariant across the Dbus session bus in Qt between 2 simple applications. Span is a simple class that contains 2 double type properties. I have successfully sent and recovered a QVariant containing just a QString across the dbus interface in the same manner I am trying to do below with a QVariant of a custom class.

Span contains the following declaration for the QMETATYPE QVariant registration in the class header file:

Q_DECLARE_METATYPE(Span)

I have 2 test applications, one sender and one receiver - both have exactly the same 'Span' class definitions. In my sender app I do this:

qDebug() << "Sending QVariant Span to receiver...";
//int spanID = QMetaType::type("Span");
Span span(100,0.5);
//QVariant settingVariant(spanID, &span);
//QVariant settingVariant(QString("HELLO"));
QVariant settingVariant;
settingVariant.setValue(span);

QDBusVariant setting( settingVariant );
response = client->setSetting(setting);
qDebug() << "RESPONSE: " << response;

QVariant result = setting.variant(); // THIS WORKS - I can just extract my 'Span' here with the correct property values set
QVariant test = QVariant::fromValue(result);
Span testSpan = test.value<Span>();
qDebug() << "Setting Span to -- Low: " << testSpan.m_lowTemp 
         << "High: " << testSpan.m_highTemp;

The 'setSetting' method is defined as:

inline QDBusPendingReply<int> setSetting(const QDBusVariant setting)
{
    QList<QVariant> argumentList;
    argumentList << QVariant::fromValue(setting);
    return asyncCallWithArgumentList(QLatin1String("setSetting"), argumentList);
}

In the receiver, I register the 'Span' class like this:

qRegisterMetaType<Span>();
qDBusRegisterMetaType<Span>();

and then I attempt to recover the Span class like so:

int DbusServerTemplate::setSetting( const QDBusVariant &setting ) {
    QVariant result = setting.variant();
    QVariant test = QVariant::fromValue(result);
    Span stuff = test.value<Span>();
    qDebug() << "Setting Span to -- Low: " << stuff.m_low 
             << "High: " << stuff.m_high;

The above code gives me bogus values for the Span class properties:

Setting Span to -- Low:  1.44144e-305 High:  5.24729e-261

What am I doing wrong? I can encode and decode the Span instance in the Sender app but once the receiver class gets it over dbus I'm getting bogus values. I'd really appreciate any ideas / help!

NOTE: I did implement the streaming operators in my Span class as follows ( the same class implementation is present in both the receiver and sender app ):

// Simple getters for the low and high temps
double Span::getHighTemp() const { return m_high; }
double Span::getLowTemp() const { return m_low; }

// Marshall the Data data into a D-Bus argument
QDBusArgument &operator<<(QDBusArgument &argument, const Span &span)
{
   argument.beginStructure();

   double high = span.getHighTemp();
   double low = span.getLowTemp();
   argument << high;
   argument << low;
   argument.endStructure();

   return argument;
}

// Retrieve the Data data from the D-Bus argument
const QDBusArgument &operator>>(const QDBusArgument &argument, Span &span)
{
   double high, low;

   argument.beginStructure();
   argument >> high;
   argument >> low;
   argument.endStructure();
   span.m_high = high;
   span.m_low = low;

   return argument;
}

来源：https://stackoverflow.com/questions/14086545/qt-qdbus-sending-custom-types-with-qvariant

标签

c++

dbus

qvariant

qdbus