class MyWidget : public QWidget
{
Q_OBJECT
public:
  MyWidget(QWidget* parent=0) : QWidget(parent)
  {
    m_toolbut1=new QToolButton(this);
    m_toolbut1->setText("Start");
    connect(m_toolbut1,SIGNAL(clicked()),this,SLOT(onToolButClicked()));
  }
public slots:
  void onToolButClicked()
  {
    if (m_toolbut1->text()=="Start")
      m_toolbut1->setText("Stop");
    else m_toolbut1->setText("Start");
  }
private:
  QToolButton* m_toolbut1;
};