Signal emitted but slot not getting called?

[SPlatten]

I have a signal:

signal:
    void write(QJsonObject& robjJSON);

In the same class I have a slot:

public slots:
    void onWrite(QJsonObject& robjJSON);

In my constructor I connect the signal and slot:

QObject::connect(this, &clsMsgSender::write
                ,this, &clsMsgSender::onWrite);

The signal is being emitted and I've verified this with the debugger, but the slot which has a breakpoint on the first line of the function does not get called:

void clsMsgSender::onWrite(QJsonObject& robjJSON) {
    QMutexLocker lock(&mMutex);
    //Add the message ID    
    robjJSON.insert(clsMsgSender::mscszMsgID, QString::number(++muint32MID));
    //Associate this TCP socket with the output data stream
    QByteArray arybytMsg;
    arybytMsg = QJsonDocument(robjJSON).toJson(QJsonDocument::Compact);
    //Write message
    qint64 int64Written = mpsckClient->write(arybytMsg);

    if ( int64Written > 0 ) {
        QString strMsg(arybytMsg);
        qdbg() << QString("onWrite::run[%1]: %2").arg(int64Written).arg(strMsg);
    }
}

Is there anything I can do that would help me find out why it isn't working?

[SPlatten]

Found the issue:

QObject::connect: Cannot queue arguments of type 'QJsonObject&'
(Make sure 'QJsonObject&' is registered using qRegisterMetaType().)

However, I was unable to find a way to reference a reference to an object as a parameter, so in the end I had to change the parameter type to a pointer.

QJsonObject*

[SPlatten]

Found the issue:

QObject::connect: Cannot queue arguments of type 'QJsonObject&'
(Make sure 'QJsonObject&' is registered using qRegisterMetaType().)

However, I was unable to find a way to reference a reference to an object as a parameter, so in the end I had to change the parameter type to a pointer.

QJsonObject*

[kshegunov]

@SPlatten said in Signal emitted but slot not getting called?:

However, I was unable to find a way to reference a reference to an object as a parameter, so in the end I had to change the parameter type to a pointer.

Because between threads a reference to an object makes very little sense with a queued connection. What will have happened is you getting a dangling reference after scope of the emission goes out and your receiver operating over an invalid object. Queuing a pointer makes just as little sense in this case, just use a plain value, QJsonObject is already a value-class and does the right thing.

To use references directly one'd switch to Qt::DirectConnection but then one must make sure access it thread-safe (manually ensuring that).

PS.
In your example that'd mean switching to const QJsonObject &, and Qt is going to serialize the object(s) properly.