NetworkManager StatusChanged D-Bus signal not being received.

Vaquita Tim

I'm trying to put together some code to check the NetworkManager status. The final goal is to run this on an embedded system, but for testing I am running this on Ubuntu 24, where I think it should be working.

I am trying to connect to the StateChanged D-Bus signal, with the following code :-

const QString s_NMService( "org.freedesktop.NetworkManager" );
const QString s_NMObjectPath( "/org/freedesktop/NetworkManager" );
const QString s_NMInterface( "org.freedesktop.NetworkManager" );

CNetworkManager::CNetworkManager(QObject *parent)
		: QObject(parent),
//QDBusInterface's constructor makes a non-obvious blocking call to introspect the D-Bus service
		m_NM( s_NMService, s_NMObjectPath, s_NMInterface, QDBusConnection::systemBus() )
{
	const QVariant VarState( m_NM.property( "State" )  );
	m_NMState = static_cast<ENMState>( VarState.toUInt() );

	m_bWasConnected = QDBusConnection::systemBus().connect(
						s_NMService, s_NMObjectPath, s_NMInterface,
						"StateChanged", "(u)",
						this, SLOT(SetNMState(uint)) );
	m_Connect = connect( &m_NM, SIGNAL(StateChanged(uint)), this, SLOT(SetNMState(uint)) );

However, my debugger tells me that, although the State is correctly fetched initially, the slot function is not called (it should be called twice, of course, since I tried to connect in 2 different ways).

I have noticed this so in some sense I am in a better situation ;-)

Clearly networkmanager is not the problem :-

~$ nmcli monitor 
NetworkManager is running
enp0s3: deactivating
enp0s3: disconnected
There's no primary connection
Networkmanager is now in the 'connected (local only)' state
Connectivity is now 'limited'
enp0s3: using connection 'netplan-enp0s3'
enp0s3: connecting (prepare)
Networkmanager is now in the 'connecting' state
enp0s3: connecting (configuring)
enp0s3: connecting (getting IP configuration)
'netplan-enp0s3' is now the primary connection
enp0s3: connecting (checking IP connectivity)
enp0s3: connecting (starting secondary connections)
enp0s3: connected
Networkmanager is now in the 'connected (site only)' state
Networkmanager is now in the 'connected' state
Connectivity is now 'full'

I've checked the names and variable types using D-Feet.

I also tried running with sudo privileges.

Now I've run out of ideas.

Qt v6.8.3

If anyone with experience can spot my mistake, it would be appreciated, otherwise I will have to revert to the ugly polling option.

TIA

Tim

Vaquita Tim

I will check to see if it's due to this bug

Vaquita Tim

Or, more likely it was the dumb mistake of doing a quick hack for testing, which deleted my test object...