C#

private void OnMouseDown(object sender, MouseEventArgs e) 
{
  if (e.Button == MouseButtons.Left)
  {
      if (tabMainTabCtrl.SelectedIndex != 0)
      {
        if (IsUserAuthenticated) // this is set when user is authenticated or not
          tabMainTabCtrl.SelectedIndex = m_iSelectedTab;
        else
          tabMainTabCtrl.SelectedIndex = 0;
      }
  }
}

private void tabMainTabCtrl_SelectedIndexChanged(object sender, EventArgs e)
{
     m_iSelectedTab = tabMainTabCtrl.SelectedIndex; //m_iSelectedTab: class level global variable
}

#include <QCheckBox>
#include <QMouseEvent>

class MyCheckBox : public QCheckBox
{
public:
    void mousePressEvent(QMouseEvent *event);
};

void MyCheckBox::mousePressEvent(QMouseEvent *event)
{
    if (event->button() == Qt::LeftButton) {
        // handle left mouse button here
    } else {
        // pass on other buttons to base class
        QCheckBox::mousePressEvent(event);
    }
}

class MyWidget : public QWidget
{
public:
    bool event(QEvent *event);
};

static const int MyCustomEventType = 1099;

class MyCustomEvent : public QEvent
{
public:
    MyCustomEvent() : QEvent((QEvent::Type)MyCustomEventType) {}
};

bool MyWidget::event(QEvent *event)
{
    if (event->type() == QEvent::KeyPress) {
     QKeyEvent *ke = static_cast<QKeyEvent *>(event);
     if (ke->key() == Qt::Key_Tab) {
        return true;
     }
    } else if (event->type() == MyCustomEventType) {
     MyCustomEvent *myEvent = static_cast<MyCustomEvent *>(event);
       return true;
    }
    return QWidget::event(event);
}

int main()
{
}