1、切换前垂直布局

2、切换后水平布局

3、关键代码

    qDebug() << "开始切换布局";
    QWidget *widget = centralWidget();
    QLayout *layout = widget->layout();
    if(layout)
    {
        while(layout->count())
        {
            QLayoutItem *item = layout->takeAt(0);
            if(item->layout())
            {
                delete item->layout();
            }
            else
            {
                if(item->widget())
                {
                    delete item->widget();
                }
            }
            delete item;
        }
        delete layout;
    }

    layout = new MyHBoxLayout;

    QLabel *label1 = new MyLabel("Label 1");
    QLabel *label2 = new MyLabel("Label 2");
    QLabel *label3 = new MyLabel("Label 3");

    label1->setStyleSheet("QLabel {background : red}");
    label2->setStyleSheet("QLabel {background : green}");
    label3->setStyleSheet("QLabel {background : blue}");

    layout->addWidget(label1);
    layout->addWidget(label2);
    layout->addWidget(label3);
    widget->setLayout(layout);

    qDebug() << "完成切换布局";