Qt QDbus Sending Custom Types with QVariant

[phil999]

I'm trying to send a custom class ( "Span" ) inside a QVariant across the Dbus session bus in Qt between 2 simple applications. I am using Qt Version 4.8.1 ( but see the same results with 4.8.3 ) 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)

Q_DECLARE_METATYPE(Span)

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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;

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;

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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);
    }

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

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

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

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

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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;

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;

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

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

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

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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!

[anda_skoa]

Did you implement the streaming operators for converting your type from and to QDBusArgument?

E.g. see example here http://qt-project.org/doc/qt-4.8/qdb...t.html#details

Cheers,
_

[phil999]

Hi there, yes I did here they are - I can extract the properties on the sender application after constructing my Span instance, but just not after receiving it via DBus in the receiver app.

// Simple getters for the low and high temps
double Span::getHighTemp() const { return m_highTemp; }
double Span::getLowTemp() const { return m_lowTemp; }
 
// 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_highTemp = high;
   span.m_lowTemp = low;
 
   return argument;
 
}

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

// 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_highTemp = high;
   span.m_lowTemp = low;

   return argument;

}

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