QMessageBox* msgBox = new QMessageBox( this );
    //msgBox->setAttribute( Qt::WA_DeleteOnClose ); //makes sure the msgbox is deleted automatically when closed
    msgBox->setStandardButtons( QMessageBox::Ok );
    msgBox->setWindowTitle( tr("Warning") );
    msgBox->setText( tr("The operation may take a long time. Please wait.") );

    msgBox->setModal( false ); // if you want it non-modal
    msgBox->open( this, SLOT(msgBoxClosed(QAbstractButton*)) );

    //QSharedPointer<QDir> dir = QSharedPointer<QDir>::create(lastDir_);
    QApplication::setOverrideCursor(QCursor(Qt::WaitCursor));