Qt c++ signal slots does not work properly

Question

My code has a strange behaviour:

I want to set a signal-slot connection. When I do not have any parameters it works fine. But when I use parameters even as as easy ones like int my connection doesn`t work. Does anybody has a clue as to why that may be?

Thank you.

This works:

Chart.h       
  void signalForUI();

Chart.cpp
    emit signalForUI();

Userinterface.h   
    public slots:
      void UI_schreibtWas();

 Userinterface.cpp   

     connect(  ui.Diagram  , SIGNAL( signalForUI()  ),
               this  ,SLOT (UI_schreibtWas()))  ;
  ...

       void UserInterface::UI_schreibtWas()
       {  qDebug() << "ich schreibe was- ohne ";    }

This doesn`t:

Chart.h       
  void signalForUI(const int &X_send);

Chart.cpp
    emit signalForUI(5);        

Userinterface.h   
    public slots:
      void UI_schreibtWas(const int &X_send);

 Userinterface.cpp   

     connect(  ui.Diagram  , SIGNAL( signalForUI(const int &X_send)  ),
               this  ,SLOT (UI_schreibtWas(const int &X_send)))  ;
  ...

      void UserInterface::UI_schreibtWas(const int &X_send)
      {  qDebug() << "ich schreibe was  - int ";    }

Answer 1

You're not supposed to pass parameter names into signal/slot definitions for connect .

connect(ui.Diagram, SIGNAL(signalForUI(const int&)),
        this, SLOT(UI_schreibtWas(const int&)));

But you should use the Qt 5 syntax for connect, which does not use macros and allows you to catch such errors at compile time:

connect(ui.Diagram, &DiagramClass::signalForUI, this, &ThisClass::UI_schreibtWas)

Replace DiagramClass and ThisClass with appropriate class names.