How to use new signal/slot syntax in Qt5.6?

[kahlenberg]

Hi,
I have a console application, I want to connect a signal from an object to a function in main.cpp. According to new signal/slot syntax it is possible. There is no need to have an object in order to connect signals and slots. How can I do that?

main.h

....
void dumpReceivedData(int type, QByteArray *msg);

main.cpp

int main()
{
...
Server server;
QObject::connect(&server, Server::msgOut, dumpReceivedData);
....
}
void dumpReceivedData(int type, QByteArray *msg)
{
qDebug() << msg->constData();
}

server.h

...
signals:
static void msgOut(int type, QByteArray *msg);

server.cpp

void foo()
{
...
QByteArray *msg = new QByteArray;
msg->append(aTcpSocket->readAll());
emit msgOut(1, msg);
}

I am getting compile error:

no matching function for call to QObject::connect(Server *, void(&)(int, QByteArray*), void(&)(int, QByteArray*))

Thanks.

[J.Hilk]

@kahlenberg

Taken from the docu

QObject::connect(const QObject *sender, PointerToMemberFunction signal, const QObject *receiver, PointerToMemberFunction method, Qt::ConnectionType type = Qt::AutoConnection)

in the case you describted:

QObject::connect(&server, &Server::msgOut, this, &MyClass::dumpReceivedData);

[hskoglund]

Hi, try moving the &, like this:

...
Server server;
QObject::connect(server, &Server::msgOut, dumpReceivedData);
....

[kahlenberg]

@J.Hilk
Thanks for reply but as I described above, I don't want to connect signals/slot between two objects, instead, I want to connect one object's signal to a function in main.cpp, where there is no class.

[J.Hilk]

@kahlenberg
Ah, I see, you want a lambda connection to a signal, ok

connect(&server, &Server::msgOut, [=]{ myFunction();});
//if you want to pass variables too
connect(&server, &Server::msgOut, [=](QVariant a){
    //do stuff with a or not
    myFunction(a);});

[beecksche]

@kahlenberg

You can also connect your signal with a static function. It's nearly the same with the connection to a lamba function, like @J-Hilk said.

static void staticSlot() 
{
 ...
}

int main()
{
 ...
 QObject::connect(&yourObject, &YourObject::yourSignal, staticSlot);
 ...
}

So in your case you just should add static to your void dumpReceivedData(int type, QByteArray *msg) function.

[VRonin]

QObject::connect(&server, &Server::msgOut, dumpReceivedData);

[jsulm]

@beecksche static is of no use in this case. See http://stackoverflow.com/questions/558122/what-is-a-static-function

[kahlenberg]

@beecksche, @VRonin
with or without static definition of the function dumpReceivedData
Compile error:

no matching function call to 'QObject::connect(Server *, void(*)(int, QByteArray*), void (&)(int, QByteArray*))'

@J-Hilk

QObject::connect(&server, &Server::msgOut, [=](int type, QByteArray *msg)
{
    dumpReceivedData(type, msg);
}
);

compile error:

no matching function for call to QObject::connect(Server *, void(*)(int, QByteArray*), main(int, char**)::__lambda0)

[VRonin]

this works for me, could you test it?

#include <QApplication>
#include <QTimer>
#include <QDebug>
#include <QDateTime>
void printTime(){
    qDebug() << QDateTime::currentDateTime();
}

int main(int argc, char* argv[])
{
    QApplication app(argc, argv);
    QTimer t;
    t.setInterval(1000);
    QObject::connect(&t, &QTimer::timeout, printTime);
    t.start();
    return app.exec();
}

[kahlenberg]

It worked. I declared the function dumpReceivedData as static mistakenly. I deleted static keyword and it worked.
I also tested lambda function. It also worked.
Thanks a lot.