How to display data from MQTT server in real-time?

[GrecKo]

That looks like a job for a Q_PROPERTY and not for a signal.

Store the message payload in a member variable of your class, let's say QString m_message.

In your header you'd use a Q_PROPERTY(QString message READ message NOTIFY messageChanged)

Implementation of the getter:
QString message() { return m_message; }

Add a signal void messageChanged(); in your header.
And modify your exisiting onMQTT_Received to be :

void MyDataClass::onMQTT_Received(const QMQTT::Message &message)
{
    m_message = message.payload();
    emit messageChanged();
}

Then in your QML you can just do:

Label {
    text: myobj.message
}

Nice and clean declarative code, no need to deal with Connections and signals in QML.

[AntonioQt]

Awesome @GrecKo!
Thank you so much. It worked for me.

This was indeed easier. I tried it earlier but couldn't succeed, but the way explained was very explanatory.
So now I understood two exposing data to QML.

Thank you everyone!

[SGaist]

On a side note, the getter should be const, it doesn't modify anything in the class instance.