该示例演示了一个"扩张的窗口"，主窗口的布局为水平布局，内置两个子窗口，采用定时器设置左边窗口的宽度，达到控制"扩张"的目的。

#include <QApplication>
#include <QWidget>
#include <QHBoxLayout>
#include <QTimer>

class MyWidget : public QWidget
{
	//Q_OBJECT
public:
	MyWidget(QWidget* parent = nullptr) : QWidget(parent)
	{
		setFixedSize(600, 400);
		hLayout = new QHBoxLayout(this);

		widget1 = new QWidget(this);
		widget1->setFixedWidth(20);
		widget1->setStyleSheet("background-color:red;");

		widget2 = new QWidget(this);

		hLayout->addWidget(widget1);
		hLayout->addWidget(widget2, 1);
		widget2->setStyleSheet("background-color:green;");
		m_timer = new QTimer(this);

		m_timer->start();
		m_timer->setInterval(100);
		QObject::connect(m_timer, &QTimer::timeout, [=]() {
			int nW = widget1->width() + 1;
			if (nW >= 100)
				return;
			widget1->setFixedWidth(nW);
			});
	}



private:
	QWidget* widget1;
	QWidget* widget2;
	QHBoxLayout *hLayout;
	QTimer* m_timer;
};

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

	MyWidget w;

	w.show();

	return app.exec();
}