QtDBus com::blah::test Interface fails to receive dbus-send signals and unittest signals

[sayo9394]

I already posed the question on Stackoverflow and can be found here:
https://stackoverflow.com/questions/57050454/qtdbus-not-receiving-signals-from-dbus-send-when-using-qt-dbus-xml-interface

System information:
QT5.10
Ubuntu 16.04

I'm fairly new to QT development, and for the past few weeks have been successfully developing a QtDBus application structured around DBus signals only, with unittest and BDD test (python scripts + dbus-send) and all has been going well.

<!DOCTYPE node PUBLIC "-//freedesktop//DTD D-BUS Object Introspection 1.0//EN http://www.freedesktop.org/standards/dbus/1.0/introspect.dtd">
<node>
<interface name="com.blah.XYZ">
    <signal name="Event">
        <arg name="event_json" type="s" direction="out"/>
    </signal>
    <method name="AuthenticateUser">
        <arg name="auth_req_json" type="s" direction="in"/>
        <arg name="result" type="s" direction="out"/>
    </method>
</interface>
</node>

Now that I wanted to add dbus method calls, I found that I'm unable to make those calls through the Qt interface created from the xml. Then I realised this whole time I was creating the interface with empty strings for the service name, and path. I was following the DBUS Chat example that creates interface same way i'm doing below.

#include "xyz_interface.hxx"
com::blah::Xyz interface = new com::blah::Xyz(QString(), QString(), QDBusConnection::systemBus(), this);
connect(interface , &com::blah::Xyz::Event, this, &SomeClass::HandleEvents)

unit test as such worked in triggering HandleEvents function;

QDBusMessage xyz_signal = QDBusMessage::createSignal(
"/com/blah/XYZ", "com.blah.XYZ", "Event");
xyz_signal << "hello";
ASSERT_TRUE(connection.send(xyz_signal ));

this dbus-send command worked in triggering HandleEvents function

dbus-send --system --type=signal /com/blah/XYZ com.blah.XYZ.Event string:"hello"

The way I confirmed that I'm unable to call methods, I created a python test dbus service that printed hello when the method call to it was successful. Using d-feet I was able to call the python method, but not able to do so from my QT code.

When I created the interface using actual name and path as such;

com::blah::XYZ interface = new com::blah::XYZ("com.blah.XYZ", "/com/blah/XYZ", QDBusConnection::systemBus(), this);

Then I was able to call the interface method interface->AuthenticateUser(str) from the python dbus service, but now i'm unable to receive any signals sent by dbus-send or the unit test code is failing.

pls help!

Cheers,
Simon