Qt无法在小部件上绘制多个QRect

#include <QtWidgets>

class MyWidget : public QWidget {
public:
    MyWidget(QWidget *parent = nullptr) : QWidget(parent) {}

protected:
    void paintEvent(QPaintEvent *event) override {
        QPainter painter(this);
        painter.setPen(Qt::black);
        painter.setBrush(Qt::red);

        // 绘制多个矩形
        painter.drawRect(QRect(10, 10, 50, 50));
        painter.drawRect(QRect(70, 10, 50, 50));
        painter.drawRect(QRect(130, 10, 50, 50));
    }
};

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

    MyWidget widget;
    widget.show();

    return app.exec();
}