Error: symbol(s) not found for architecture x86_64, collect2: ld returned 1 exit status

I have been struggling for a while with an issue on Qt.

Here is my code:

hexbutton.h:

#ifndef HEXBUTTON_H
#define HEXBUTTON_H

#include <QPushButton>
#include <QWidget>
#include <QIcon>

class HexButton : public QPushButton
{
    Q_OBJECT

public:
    HexButton(QWidget *parent, QIcon &icon, int i, int j);

public slots:
    void changeIcon();
};

#endif // HEXBUTTON_H

Hexbutton.cpp:

#include "hexbutton.h"

HexButton::HexButton(QWidget *parent, QIcon &icon, int i , int j) : QPushButton(parent){
    //setFlat(true);
    setIcon(icon);
    setGeometry((i*40)+((j*40)/2), j*40, 40, 40);
}

void HexButton::changeIcon(){
        setIcon(QIcon("/Users/jonathanbibas/Documents/Workspace Qt/Test/hexagon.gif"));
}

MyWindow.h:

#ifndef MYWINDOW_H
#define MYWINDOW_H

#include <QApplication>
#include <QWidget>
#include <QPushButton>
#include <QLCDNumber>
#include <QSlider>
#include <QProgressBar>
#include "hexbutton.h"



class MyWindow : public QWidget
{

public:
    MyWindow();
    ~MyWindow();

private:
    HexButton * myButtons[11][11];
};



#endif // MYWINDOW_H

MyWindow.cpp:

#include "MyWindow.h"
#include <QColor>
#include <QIcon>


MyWindow::MyWindow() : QWidget() {


    setFixedSize(740, 440);

    QIcon icon = QIcon("/Users/jonathanbibas/Documents/Workspace Qt/Test/whitehexagon.png");

    for(int i =0 ; i < 11 ; i ++){
        for(int j =0 ; j < 11 ; j ++){


            myButtons[i][j] = new HexButton(this, icon, i, j);

            QObject::connect(myButtons[i][j], SIGNAL(clicked()), myButtons[i][j], SLOT(changeIcon()));
        }
    }
}



MyWindow::~MyWindow()
{
    delete myButtons;

}

And finally, Main.cpp:

#include <QApplication>
#include "MyWindow.h"


int main(int argc, char *argv[])
{
    QApplication app(ar