Why can't Qt build my project after including a QStackedWidget-inherited class?

Question

I want to subclass the "QStackedWidget" class to add some public slots but when I add its header and source to my Qt project, my project can't be built completely and after showing many compiling errors and warnings, Qt gets crashed.

This is my QStackedWidget-inherited class header below:

#ifndef QSTACKEDWIDGETV2_H
#define QSTACKEDWIDGETV2_H

#include <QWidget>
#include <QStackedWidget>

class QStackedWidgetV2 : public QStackedWidget
{
public slots:
  void GoToNextPage();
  void GoToBackPage();
  void JumpToPage(qint32 index);
public:
  QStackedWidgetV2();
  ~QStackedWidgetV2();
}

#endif // QStackedWidgetV2

And these are some of the given compiling and warning errors. However, Qt showed me a lot of other errors but they were similar: