sender null on functor receiver of connect(const QObject *sender, PointerToMemberFunction signal, Functor functor) ? :'(

[mbruel31]

Hi,
I'm doing this kind of connection connect(this, &ScopedSignal::scopedSignalReply, m_receivingSlot);
with m_receivingSlot being of type: std::function<void()>
initialized with: std::bind(&NotificationList::onNotificationsReadReply, this)

and my receiving slot:

void NotificationList::onNotificationsReadReply()
{
    QObject * s = sender();
...
}

My sender is null :(
I need it as it is the key of a Map where I should delete the associated service...
Any idea?

[Christian Ehrlicher]

Then use a simple lambda function

connect(this, &ScopedSignal::scopedSignalReply, this, [this]() { onNotificationsReadReply(this); }

[mbruel31]

@Christian-Ehrlicher great this does the job perfectly! \o/ I've extra parameters in my lambda but that a great workaround.
I still would like to understand why the sender is null.
I've never checked the underlying code of functor connection but I would expect it should be able to retrieve the sender...
Anybody else had this issue?
Is it something specific to the functor signature that is processed just like a C callback maybe?
Interesting to know about no?

[JonB]

@mbruel31
Because sometimes QObject::sender() is not set/invalid. In any case, it was first obsoleted by QSignalMapper and now by lambdas.

[Christian Ehrlicher]

@mbruel31 said in sender null on functor receiver of connect(const QObject *sender, PointerToMemberFunction signal, Functor functor) ? :'(:

Is it something specific to the functor signature that is processed just like a C callback maybe?

To few information - it can be e.q. a QueuedConnection due to thread context switch or similar.

[mbruel31]

hum didn't know QSignalMapper..
well same thread, direct connection, that's why I don't understand...
anyway, not an issue, I can use lambda :)