error: 'QDesktopServices' has not been declared

Worked before and now it seems broken I don't know how to resolve this got any clue?:confused:

mainWindow.cpp: In member function 'void mainWindow::homepage()':
mainWindow.cpp:123: error: 'QDesktopServices' has not been declared
mainWindow.cpp:123: error: invalid type in declaration before '(' token
mainWindow.cpp:123: error: cannot convert 'QUrl' to 'int' in initialization
mainWindow.cpp:123: warning: unused variable 'openUrl'

Code:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
 
#include <QWidget>
#include <QMenuBar>
 
class mainWindow : public QWidget
{
    Q_OBJECT
 
public:
    mainWindow(QWidget *parent = 0);
	~mainWindow();
	void createMenu();
 
public slots:
	void homepage();
 
private:
	QMenuBar *menuBar;
	QMenu *fileMenu;
	QAction *openAction;
	QAction *saveAction;
	QAction *saveAsAction;
	QAction *exitAction;
};

Code:

#include <QLayout>
#include <QDesktopServices>
#include <QUrl>
#include "mainWindow.h"
#include "floorBoard.h"
 
mainWindow::mainWindow(QWidget *parent)
    : QWidget(parent)
{
	createMenu();
 
	floorBoard *fxsBoard = new floorBoard(this);
 
	QVBoxLayout *mainLayout = new QVBoxLayout;
	mainLayout->setMenuBar(menuBar);
	mainLayout->addWidget(fxsBoard);
	mainLayout->setMargin(0);
	mainLayout->setSpacing(0);
	mainLayout->setSizeConstraint(QLayout::SetFixedSize);
	setLayout(mainLayout);
};
 
mainWindow::~mainWindow()
{
 
};
 
void mainWindow::createMenu()
{
    menuBar = new QMenuBar;
 
    QMenu *fileMenu = new QMenu("&File", this);
	QAction *openAction = fileMenu->addAction("&Open File...");
	QAction *saveAction = fileMenu->addAction("&Save");
	QAction *saveAsAction = fileMenu->addAction("Save &As...");
	fileMenu->addSeparator();
    QAction *exitAction = fileMenu->addAction("E&xit");
    menuBar->addMenu(fileMenu);
 
	QMenu *helpMenu = new QMenu("&Help", this);
	QAction *homepageAction = helpMenu->addAction(" &Webpage");
    menuBar->addMenu(helpMenu);
 
    connect(exitAction, SIGNAL(triggered()), this, SLOT(close()));
	connect(homepageAction, SIGNAL(triggered()), this, SLOT(homepage()));
 
};
 
void mainWindow::homepage()
{
	QDesktopServices::openUrl(QUrl("http://www.google.com/"));
};