运行截图如下（时针，分针，秒针都可以动的哦）：

代码如下：

Widget.h

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>

namespace Ui {
class Widget;
}

class Widget : public QWidget
{
    Q_OBJECT

public:
    explicit Widget(QWidget *parent = 0);
    ~Widget();

protected:
    void paintEvent(QPaintEvent *)override;
    void resizeEvent(QResizeEvent *event)override;

    void mouseMoveEvent(QMouseEvent *event)override;
    void mousePressEvent(QMouseEvent *event)override;
    void mouseReleaseEvent(QMouseEvent *event)override;
private:
    Ui::Widget *ui;
    bool m_dragging;
    QPoint m_startPosition;
    QPoint m_framePosition;
};

#endif // WIDGET_H

Widget.cpp

#include "widget.h"
#include "ui_widget.h"

#include <QPainter>
#include <QTime>
#include <QMouseEvent>
#include <QTImer>

Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget)
{
    ui->setupUi(this);
    QTimer *timer=new QTimer(this);
    connect(timer,SIGNAL(timeout()),this,SLOT(update()));
    timer->start(1000);
    m_dragging = false;
}

Widget::~Widget()
{
    delete ui;
}

void Widget::paintEvent(QPaintEvent *){
    QPainter painter(this);
    painter.setRenderHint(QPainter::Antialiasing);
    painter.translate(width()/2,height()/2);
    int side=qMin(width(),height());
    painter.scale(side/200.0,side/200.0);

    QPen pen(Qt::black,4);
    painter.setPen(pen);
    QBrush brush(QColor(247,238,214,80));
    painter.setBrush(brush);
    painter.drawEllipse(QPointF(0,0),98,98);

    painter.setPen(Qt::white);
    painter.drawEllipse(QPointF(0,0),100,100);

    QTime time=QTime::currentTime();
    painter.setPen(Qt::NoPen);
    painter.setBrush(Qt::black);

    painter.save();
    painter.rotate(30.0 * ((time.hour() + time.minute() / 60.0)));

    static const QPoint hourHand[3] = {
        QPoint(2, 0),
        QPoint(-2, 0),
        QPoint(0, -60)
    };
    painter.drawConvexPolygon(hourHand, 3);
    painter.restore();

    static const QPoint minuteHand[3] = {
        QPoint(2, 0),
        QPoint(-2, 0),
        QPoint(0, -95)
    };

    static const QPoint secondHand[3]={
        QPoint(2,0),
        QPoint(-2,0),
        QPoint(0,-105)
    };

    painter.save();
    painter.rotate(6.0 * (time.minute() + time.second() /
                          60.0));
    painter.drawConvexPolygon(minuteHand, 3);
    painter.restore();

    painter.save();
    painter.rotate(6.0 * time.second());
    painter.drawConvexPolygon(minuteHand, 3);
    painter.restore();



    painter.save();
    painter.setPen(Qt::black);
    painter.setBrush(Qt::lightGray);
    painter.drawEllipse(QPointF(0, 0), 2, 2);
    painter.drawPoint(0, 0);
    painter.restore();

    painter.setPen(Qt::black);
    for (int i = 0; i < 12; ++i) {
        painter.drawLine(90, 0, 96, 0);
        painter.rotate(30.0);
    }
    for (int j = 0; j < 60; ++j) {
        if ((j % 5) != 0)
            painter.drawLine(95, 0, 96, 0);
        painter.rotate(6.0);
    }
}

void Widget::mousePressEvent(QMouseEvent *event){
    if(event->button()==Qt::LeftButton){
        m_dragging=true;
        m_startPosition=event->globalPos();
        m_framePosition=frameGeometry().topLeft();
    }
    QWidget::mousePressEvent(event);
}

void Widget::mouseMoveEvent(QMouseEvent *event){
    if(event->buttons()&Qt::LeftButton){
        if(m_dragging){
            QPoint delta=event->globalPos()-m_startPosition;
            move(m_framePosition+delta);
        }
    }
    QWidget::mouseMoveEvent(event);
}

void Widget::resizeEvent(QResizeEvent *event){
    int side = qMin(width(), height());
    QRegion maskedRegion(width() / 2 - side / 2, height() /
                         2 - side / 2, side, side, QRegion::Ellipse);
    setMask(maskedRegion);
}

void Widget::mouseReleaseEvent(QMouseEvent *event){
    m_dragging=false;
    QWidget::mouseReleaseEvent(event);
}

main.cpp

#include "widget.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Widget w;
    w.show();

    return a.exec();
}