#include <QApplication>

#include <QComboBox>
#include <QAbstractItemView>


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

    QComboBox cb;    
    cb.view()->setVerticalScrollBarPolicy(Qt::ScrollBarAsNeeded);


    for(int i=0; i<100; ++i)
        cb.addItem(QString::number(i));
    cb.show();

    return a.exec();
}