1 .h

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>
#include <QPaintEvent> //绘制事件
#include <QPainter> //画家类
#include <QPaintDevice>
#include <cmath> //
#include <QPainterPath>
#include <QTime> //时间类
#include <QTimer> //定时器
#include <QTimerEvent> //定时器事件
#include <QDebug>
#include <QBrush> //画刷

#define PI 3.14159

QT_BEGIN_NAMESPACE
namespace Ui { class Widget; }
QT_END_NAMESPACE

class Widget : public QWidget
{
    Q_OBJECT

public:
    Widget(QWidget *parent = nullptr);
    ~Widget();
protected:
    void paintEvent(QPaintEvent *event) override; //重写绘制事件函数
    void timerEvent(QTimerEvent *event) override; //重写定时器事件函数
    void DrawScaleLine(QPainter& painter, QPen pain_pen); //绘制刻度线函数
    void DrawSecLine(); //绘制秒针函数
    void DrawMinuLine(); //绘制分针函数
    void DrawHourLine(); //绘制时针函数
private:
    Ui::Widget *ui;
    QTimer* timer; //定时器指针
    int sec=0, minu=0, hour=0; //用于存储时分秒
};
#endif // WIDGET_H

2 .CPP

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

Widget::Widget(QWidget *parent)
    : QWidget(parent)
    , ui(new Ui::Widget)
{
    ui->setupUi(this);
    timer = new QTimer(this);//实例化
    QTime time;
    sec = time.currentTime().second();//获取当前时间
    minu = time.currentTime().minute();
    hour = time.currentTime().hour();
    //qDebug() << sec << "  " << minu;
    this->startTimer(1000);//启动定时器
}

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

void Widget::paintEvent(QPaintEvent *event)
{
    //实例化一个画家类
    QPainter pt(this);
    pt.setRenderHint(QPainter::Antialiasing, true);//开启反锯齿
    //设置画笔(RGB)
    QPen pen(QColor(255,50,70));
    pen.setWidth(8);//设置画笔宽度
    pt.translate(this->width()/2,this->height()/2);//设置画笔起点
    pt.setPen(pen);
    //绘制圆
    pt.drawEllipse(QPoint(0,0), 200, 200);
    DrawScaleLine(pt, pen);//绘制刻度线
    //实例化一个画家类
    QPainter pt_1(this);
    pt_1.setRenderHint(QPainter::Antialiasing, true);//开启反锯齿
    //设置画笔(RGB)
    QPen pen_1(QColor(0,0,0));
    pen_1.setWidth(8);//设置画笔宽度
    pt_1.translate(this->width()/2,this->height()/2);//设置画笔起点
    pt_1.setPen(pen_1);
    //绘制圆
    pt_1.drawEllipse(QPoint(0,0), 8, 8);


    DrawSecLine();  //秒针
    DrawMinuLine(); //分针
    DrawHourLine(); //时针
    //让绘制事件不断的触发
    this->update();
}

//绘制刻度线函数
void Widget::DrawScaleLine(QPainter& painter,QPen pain_pen)
{
    //粗刻度线
    for(int i=0; i<12; i++) {
        pain_pen.setWidth(6);//宽度
        pain_pen.setColor("black");
        painter.setPen(pain_pen);
        painter.drawLine(QPoint(0, 180), QPoint(0, 192));
        painter.rotate(30);
    }
    //细刻度线,上下二者可%5操作（二合一for循环）
    for(int i=0; i<60; i++) {
        pain_pen.setWidth(3);
        pain_pen.setColor("black");
        painter.setPen(pain_pen);
        painter.drawLine(QPoint(0,195), QPoint(0,190));
        painter.rotate(6);
    }
    painter.end();
}

//绘制秒针函数
void Widget::DrawSecLine()
{
    QPainter psec(this);
    //设定初始位置
    psec.translate(this->width()/2,this->height()/2);
    //锯齿取消
    psec.setRenderHint(QPainter::Antialiasing,true);
    //设置每个时钟
    //颜色
    QPen sec_pen(QColor(0, 160, 230));
    //秒针宽度
    sec_pen.setWidth(2);
    //绑定画家和笔
    psec.setPen(sec_pen);
    //秒针偏移量
    psec.rotate(sec*6);
    //设定秒针长度及初始位置
    psec.drawLine(QPoint(0,0),QPoint(0,-150));
    psec.end();
}
//绘制分针
void Widget::DrawMinuLine()
{
    QPainter pmin(this);
    //设定初始位置
    pmin.translate(this->width()/2,this->height()/2);
    //锯齿取消
    pmin.setRenderHint(QPainter::Antialiasing,true);
    //分针颜色
    QPen min_pen(QColor(0, 127, 127));
    //分针宽度
    min_pen.setWidth(6);
    //绑定画家和笔
    pmin.setPen(min_pen);
    //设定分针偏移量
    pmin.rotate(minu*6+sec*0.1);
    //设定分针长度及初始
    pmin.drawLine(QPoint(0,0),QPoint(0,-120));
    pmin.end();
}
//时针
void Widget::DrawHourLine()
{
    QPainter phou(this);
    //设定初始位置
    phou.translate(this->width()/2,this->height()/2);
    //锯齿取消
    phou.setRenderHint(QPainter::Antialiasing,true);
    //时针颜色
    QPen hou_pen(QColor(200, 100, 0));
    //秒针宽度
    hou_pen.setWidth(10);
    //绑定画家和笔
    phou.setPen(hou_pen);
    //偏移大小
    phou.rotate(hour*30+minu*0.5);
    //设定时针长度及初始位置
    phou.drawLine(QPoint(0,0),QPoint(0,-80));
    phou.end();
}
//处理定时器事件
void Widget::timerEvent(QTimerEvent *event)
{
    sec++;
    if((sec % 60) == 0)//60秒进一
    {
        sec = 0;
        minu++;
        if((minu % 60) == 0)//60分进一
        {
            minu = 0;
            hour++;
            if((hour%12) == 0)//0点
            {
                hour = 0;
            }
        }
    }
}