Support "instruction"-item in QComboBox

#include <QtGui>

class ComboBox : public QComboBox
{
    Q_OBJECT
public:
    ComboBox()
    {
        
    }

    void setDummyItem(const QString &text)
    {
        dummyText = text;
    }

    void showPopup()
    {
        removeDummy();
        QComboBox::showPopup();
    }

protected:
    void showEvent(QShowEvent *e)
    {
        addDummy();
        QComboBox::showEvent(e);
    }

private slots:
    void removeDummy()
    {
        if (!dummyText.isNull() && itemText(0) == dummyText) {
            removeItem(0);
            disconnect(this, SIGNAL(currentIndexChanged(int)), this, SLOT(removeDummy()));
        }
    }

private:
    void addDummy()
    {
        if (!dummyText.isNull() && itemText(0) != dummyText) {
            insertItem(0, dummyText);
            setCurrentItem(0);
            connect(this, SIGNAL(currentIndexChanged(int)), this, SLOT(removeDummy()));
        }
    }

    QString dummyText;
};

#include "main.moc"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    ComboBox cb;
    cb.addItems(QStringList() << "Euro" << "USD" << "Yen" << "GBP");
    cb.setDummyItem("Select Currency...");
    cb.show();
    

    return a.exec();
}