Qt Slot没有被叫

Question

I got a program in which I connect with a QSignalMapper multiple signal from object to a slot in the main program:

class A()
{
    private:
        QSignalMapper * signalMapperRead_;
        std::vector<Service*> services_;
    public:
    void initConnection()
    {
        signalMapperRead_ = new QSignalMapper();

        connect(signalMapperRead_, SIGNAL(mapped(int)), this, SLOT(readyToSendToService(int)));

        for ( size_t i = 0 ; i < services_.size() ; ++i )
        {
            connect(services_.at(i), SIGNAL(readyToSendToServer()), signalMapperRead_, SLOT(map()));
            signalMapperRead_->setMapping(services_.at(i), (int)i);
        }
    }

    int run()
    {
        initConnection();
        for(;;)
        {
             //do stuff;
        }
    }

};

int main()
{
    QApplication app(argc, argv);
    A * a  = new A();
    a->run();
    return app.exec
}

then, as the program is a kind of server i make him loop, and waiting for new client, ...

But the slot is never called. I am thinking that maybe it's because the program is always in the loop and never check if a signal has been emitted.

Can you please help me

Answer 1

Don't use your own loop, create a QApplication and call its exec() method.

You have to call QApplication::exec() for Qt to deliver signals.

Edit for changed code: Just remove the for(;;)-Loop, it's uneccessary. QApplication::exec() has its own loop.

Answer 2

But the slot is never called.

The Qt documentation about QApplication::exec says:

Enters the main event loop and waits until exit() is called [...]. It is necessary to call this function to start event handling. The main event loop receives events from the window system and dispatches these to the application widgets. [...] Generally, no user interaction can take place before calling exec() . [...]

This means that it's the exec method that takes care of the signal-slot system. You are calling A::run (before the exec function) which contains an for(;;) infinite loop which will block the real loop from being executed leading to your signals to be lost.

Answer 3

I have found a work-around. Beside I am not sure it's very efficient, my solution is to start a QEventLoop at every cycle of my for(;;) loop, and I made this QEventLoop quit on a QTimer timeout