Prevent QPixmap from being moved out of QGraphicsView

[Macok]

I'd like to write very simple game.
Here's a part of code:

QGraphicsScene *scene=new QGraphicsScene;
QGraphicsPixmapItem *pixmap=scene->addPixmap(QPixmap("img.png"));
ui->graphicsView->setScene(scene);

QGraphicsScene *scene=new QGraphicsScene;
QGraphicsPixmapItem *pixmap=scene->addPixmap(QPixmap("img.png"));
ui->graphicsView->setScene(scene);

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pixmap is a creature that can be moved by player using WSAD keys.
I did it by this way:

void MainWindow::keyPressEvent(QKeyEvent *event){
    switch(event->key()){
        case Qt::Key_D:
            pixmap->setPos(pixmap->pos().x()+1, pixmap->pos().y());
        break;
        case Qt::Key_A:
            pixmap->setPos(pixmap->pos().x()-1, pixmap->pos().y());
        break;
        (...)
    }
}

void MainWindow::keyPressEvent(QKeyEvent *event){
    switch(event->key()){
        case Qt::Key_D:
            pixmap->setPos(pixmap->pos().x()+1, pixmap->pos().y());
        break;
        case Qt::Key_A:
            pixmap->setPos(pixmap->pos().x()-1, pixmap->pos().y());
        break;
        (...)
    }
}

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Now i want to prevent pixmap from being moved out of QGraphicsView.
How can I do it?
Thanks in advance.