Qtwebkit and webview

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C++

hi i am using qtwebkit
i have two forms .the first is my main window and have a push button . in slot clicked of it i want to show my second form and using webview show a url (just as a simple test) but webview does not show the url . what is wrong ?
here is my code :
my main window header :

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <qmainwindow>

namespace Ui {
    class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

private:
    Ui::MainWindow *ui;

private slots:
    void on_pushButton_pressed();
};

#endif // MAINWINDOW_H
</qmainwindow>

my main window source file :

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "webview.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::on_pushButton_pressed()
{
    webview *w = new webview();
    w->show();
    w->setURL(QUrl("www.google.com"));



}

my webview header file :

#ifndef WEBVIEW_H
#define WEBVIEW_H

#include <qmainwindow>
#include <qurl>

namespace Ui {
    class webview;
}

class webview : public QMainWindow
{
    Q_OBJECT

public:
    explicit webview(QWidget *parent = 0);
    ~webview();
    void setURL(const QUrl&);

private:
    Ui::webview *ui;
};

#endif // WEBVIEW_H
</qurl></qmainwindow>

my webview source file :

#include "webview.h"
#include "ui_webview.h"
#include <qmessagebox>

webview::webview(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::webview)
{
    ui->setupUi(this);
}

webview::~webview()
{
    delete ui;
}

void webview::setURL(const QUrl& url)
{

    QMessageBox::information(0,"1","2");
    ui->webView->load(url);

}
</qmessagebox>

and my main file :

#include 
#include "mainwindow.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

    return a.exec();
}