Combobox'es dropdown is not resized after elided text applied

I'm reimplementing paintEvent for QComboBox and paint for delegate, based on QStyledItemDelegate. The problem is with my code, the text is elided, but the size of the background is not. What can be the reason, which object is responsible for this background?

delegate's paint reimplemented method:

void myDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option,
                                              const QModelIndex &index) const
{
    QStyleOptionViewItem opt = option;
    initStyleOption(&opt, index);

    opt.rect.setWidth(_parentComboRect->width());// gets parent's size
    opt.textElideMode = Qt::ElideRight;

    const QWidget *widget = opt.widget;
    QStyle *style = widget ? widget->style() : QApplication::style();

    style->drawControl(QStyle::CE_ItemViewItem, &opt, painter, widget);
}

Any suggestions?

I found the solution!

void MyCombo::showPopup() // an overridden function
{
    view()->window()->setFixedWidth(100);// ->window() makes that field!
    QComboBox::showPopup();
}