#include <QtGui>

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

    for (int i = 0; i < 100; i++)
    {
            cb.addItem(QString("Item %1").arg(i));
    }

    cb.showPopup();
    cb.show();
    cb.clear();

    for (int i = 0; i < 5; i++)
    {
            cb.addItem(QString("Item %1").arg(i));
    }

    return a.exec();
}