QTextBrowser for Helper

I am trying to make a helper with QTextBrowser. As I understood, home(), backward() and forward() are already implemented in QTextBrowser and required only connections to the buttons. Below there is .h and .cpp files

#ifndef HELPWINDOW_H
#define HELPWINDOW_H

#include <QDialog>

namespace Ui {
class HelpWindow;
}

class HelpWindow : public QDialog
{
    Q_OBJECT

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

private slots:

private:
    Ui::HelpWindow *ui;
};


#endif // HELPWINDOW_H

and

#include "helpwindow.h"
#include "ui_helpwindow.h"

HelpWindow::HelpWindow(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::HelpWindow)
{
    ui->setupUi(this);

// connection
    connect(ui->pushButton_home,SIGNAL(clicked()),ui->textBrowser,SLOT(home()));
    connect(ui->pushButton_forward,SIGNAL(clicked()),ui->textBrowser,SLOT(forward()));
    connect(ui->pushButton_backward,SIGNAL(clicked()),ui->textBrowser,SLOT(backward()));
}

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

There is no any error message. It is possible to read and click the links inside QTextBrowser. Only there are no any actions with buttons. What do I miss here?

I found why it did not work. The initial source should be specify:

ui->textBrowser->setSource(QUrl::fromLocalFile("help/index.html"));

Thank you, Jens for spending time.