选择QGraphicsItem时调用什么方法

#include <QApplication>
#include <QGraphicsScene>
#include <QGraphicsView>
#include <QGraphicsItem>
#include <QResizeEvent>

class MyGraphicsItem : public QGraphicsItem {
public:
    MyGraphicsItem() {
        setFlag(QGraphicsItem::ItemHasNoContents);
    }

    virtual QRectF boundingRect() const {
        return QRectF(0, 0, 100, 100);
    }

    virtual void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget) {
        painter->setRenderHint(QPainter::Antialiasing);
        painter->setBrush(Qt::blue);
        painter->drawRect(boundingRect());
    }
};

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

    QGraphicsScene scene;
    QGraphicsView view(&scene);
    view.setRenderHint(QPainter::Antialiasing);

    MyGraphicsItem item;
    scene.addItem(&item);

    view.setViewportUpdateMode(QGraphicsView::SmartViewportUpdate);
    view.setInteractive(true);

    view.show();

    return app.exec();
}