如何在Qt中显示GridLayout中的网格线？

#include <QtWidgets>

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

protected:
    void paintEvent(QPaintEvent* event) override {
        Q_UNUSED(event);

        QPainter painter(this);
        QPen pen(Qt::black, 1, Qt::SolidLine);
        painter.setPen(pen);

        int rowCount = layout()->rowCount();
        int columnCount = layout()->columnCount();

        for (int row = 0; row < rowCount; ++row) {
            for (int col = 0; col < columnCount; ++col) {
                QRect rect = layout()->cellRect(row, col);
                painter.drawRect(rect);
            }
        }
    }
};

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

    QWidget container;
    QGridLayout layout(&container);

    // 添加需要显示的控件到GridLayout中
    QLabel* label1 = new QLabel("Label 1");
    QLabel* label2 = new QLabel("Label 2");
    QLabel* label3 = new QLabel("Label 3");
    QLabel* label4 = new QLabel("Label 4");

    layout.addWidget(label1, 0, 0);
    layout.addWidget(label2, 0, 1);
    layout.addWidget(label3, 1, 0);
    layout.addWidget(label4, 1, 1);

    // 设置GridLayout的行列数
    layout.setRowStretch(0, 1);
    layout.setRowStretch(1, 1);
    layout.setColumnStretch(0, 1);
    layout.setColumnStretch(1, 1);

    // 创建自定义的GridWidget，并添加到GridLayout中
    GridWidget gridWidget;
    layout.addWidget(&gridWidget, 0, 0, 2, 2);

    container.show();

    return app.exec();
}