头文件

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>
#include <QPaintEvent>
#include <QDebug>
#include <QPainter>
#include <QTimerEvent>
#include <QTimer>
#include <QTime>

QT_BEGIN_NAMESPACE
namespace Ui { class Widget; }
QT_END_NAMESPACE

class Widget : public QWidget
{
    Q_OBJECT

public:
    Widget(QWidget *parent = nullptr);
    ~Widget();

    //绘画事件函数重写
    void paintEvent(QPaintEvent *event) override;



private slots:
    void timeout_slot();

private:
    Ui::Widget *ui;

    //定义一个定时器
    QTimer *timer;

    double h = 0;
    double m = 0;
    double s = 0;

};
#endif // WIDGET_H

函数实现

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

Widget::Widget(QWidget *parent)
    : QWidget(parent)
    , ui(new Ui::Widget)
{
    ui->setupUi(this);

    //启动定时器，每隔1000ms自动调用定时器事件处理函数
    timer = new QTimer(this);
    timer->start(1000);
    connect(timer, &QTimer::timeout, this, &Widget::timeout_slot);

}

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

void Widget::paintEvent(QPaintEvent *event)
{
    //实例化一个画家
    QPainter painter(this);

    painter.setRenderHint(QPainter::Antialiasing);
    //实例化一个画笔
    QPen pen;
    pen.setColor(QColor("black"));
    pen.setStyle(Qt::SolidLine);
    pen.setWidth(7);


    //表盘
    painter.setPen(pen);
    painter.translate(this->width()/2, this->height()/2);
    painter.drawEllipse(QPoint(0, 0), 200, 200);

    //刻度
    pen.setWidth(4);
    painter.setPen(pen);

    for(int i = 1; i <= 60; i++)
    {
        painter.save();
        painter.rotate(i*6);

        if(!(i % 5))
        {
            painter.drawLine(0, -200, 0, -175);
            painter.drawText(-20, -170, 40, 40, Qt::AlignHCenter | Qt::AlignTop, QString::number(i/5));
        }
        else
        {
            painter.drawLine(0, -200, 0, -190);
        }
        painter.restore();
    }

    //时针
    painter.save();
    pen.setColor(QColor("red"));
    pen.setStyle(Qt::SolidLine);
    pen.setWidth(6);

    painter.setPen(pen);
    painter.rotate(30*h);
    painter.drawLine(0, 0, 0, -60);
    painter.restore();

    //分针
    painter.save();
    pen.setColor(QColor("green"));
    pen.setStyle(Qt::SolidLine);
    pen.setWidth(3);

    painter.setPen(pen);
    painter.rotate(6*m);
    painter.drawLine(0, 0, 0, -100);
    painter.restore();

    //秒针
    painter.save();
    pen.setColor(QColor("blue"));
    pen.setStyle(Qt::SolidLine);
    pen.setWidth(1);

    painter.setPen(pen);
    painter.rotate(6*(s+1));
    painter.drawLine(0, 0, 0, -160);
    painter.restore();
    update();
}

void Widget::timeout_slot()
{
    QTime time = QTime::currentTime();
    h = time.hour();
    m = time.minute();
    s = time.second();

}