QComboBox as item delegate for QTableWidget in QGraphicsView can not show popup menu or crashed

 
class QComboBoxDelegate : public QItemDelegate
{
    Q_OBJECT
public:
    explicit QComboBoxDelegate(QWidget *parent = 0);
    QWidget *createEditor(QWidget *parent, const QStyleOptionViewItem &option,const QModelIndex &index) const{
        QStringList itemList;
        itemList<<"1"<<"2"<<"3"<<"4"<<"5";
        QComboBox *comboBox = new QComboBox(parent);
        comboBox->addItems(itemList);
        return comboBox;
    }
    void setEditorData(QWidget *editor, const QModelIndex &index) const{}
    void setModelData(QWidget *editor, QAbstractItemModel *model, const QModelIndex &index) const{}
    void updateEditorGeometry(QWidget *editor, const QStyleOptionViewItem &option, const QModelIndex &index) const{}
};
int main(int argc, char *argv[]){
    QApplication a(argc, argv);
    QGraphicsView graphicsView;
    QGraphicsScene scene;
    QTableWidget tableWidget(2,2);
    QComboBoxDelegate itemDelegate;

    tableWidget.setItemDelegate(&itemDelegate);
    graphicsView.setScene(&scene);
    scene.addWidget(&tableWidget);
    graphicsView.show();
    return a.exec();
}