Qt Code: 
  1. class Lines : public QMainWindow {
  2.      Q_OBJECT
  3.     public:        
  4.                 Lines(QWidget *parent = NULL);
  5.                 ~Lines();
  6.          QWidget *widget_main;};
  7.  
  8.     Lines::Lines(QWidget *parent) : QMainWindow ( parent ){
  9.      ui.setupUi(this);
  10.      widget_main = new QWidget(ui.centralwidget);
  11.            Dummy d(this);
  12.     }
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Qt Code: 
  1. class Dummy :  public QMainWindow {
  2.         Q_OBJECT
  3.       public:  
  4.         QPushButton *pushButton;
  5.         explicit Dummy(Lines *parent = 0);
  6.  
  7.     public slots:  void slot_pushButton(); };
  8.  
  9.     Dummy::Dummy(Lines *parent) : QMainWindow(parent){
  10.     pushButton = new QPushButton(parent->widget_main);
  11.     connect(pushButton, SIGNAL(clicked()), this->parent(), SLOT(slot_pushButton()));
  12.     }
  13.  
  14.     void Dummy::slot_pushButton(){
  15.  
  16.      pushButton->hide();
  17.  
  18.  
  19.     }
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WHatever I do, I never jump into the slot_pushButton()

However, If I declare and define slot_pushButton() in the class Lines it does work,
but this is not what I want. I want to reach the slot_pushButton in the Subclass