I've solved it.

To handle long I did not have to send immediately reply (even though tutorial said that we have to). And delayed reply will be send.

Also in extension, QDBusPendingReply<QString, QByteArray> reply = *call; setting expecting signature to \"say\" and not looking to xml interface.

@SGaist You're right,I did not think about it! I have to remove the systemBus, I'm not using it in reality, it's part of the project that I found on Github. Ok then I can try to make it an instance variable of the class or similer. Thank you!

I have found solution for this, using QDbusConnectionInterface instead QDbusServiceWatcher:

connect(QDBusConnection::sessionBus().interface(), &QDBusConnectionInterface::serviceRegistered, this, [=](QString a) { qDebug() <<"service R: " << a; });

@micland

WOOW!!! Thank you sooo much micland!! It works!!!
I tried a code similar to yours but some data were missing. Just needed to do a very tiny modification on your code:

qDebug() << key << value.variant().toString();

or directly

qDebug() << value.variant().toString();

Except it, it is perfect! Thank you again.
@micland said:

I have no clue why the qdbusviewer of Qt 5.6 is unable to call the DBus method but the code snippet above is working fine.

I hope it is going to change as I intend to use it or the 5.7 version very soon.

Cheers again.

@Mark81
I'm certainly not a D-Bus guru, my experience with it is somewhat limited. That said, I think QDBusReply::value can be used, provided you have registered your types.

Kind regards.

I confirm that adding the pthread library did the trick. But the question "why" is still there :)

@SGaist Okay, thanks :)