需求：

使用QT中的绘画工具与定时器工具实现简易时钟

代码实现过程：

widget.h

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>
#include<QPainter>          //引入画家类
#include<QPaintEvent>       //引入绘制事件类
#include<QTime>         //引入时间类
#include<QTimerEvent>   //引入定时器事件类
#include<QTimer>        //引入定时器类
#include<QDateTime>     //引入日期时间类
#include<QDebug>

QT_BEGIN_NAMESPACE
namespace Ui { class Widget; }
QT_END_NAMESPACE

class Widget : public QWidget
{
    Q_OBJECT

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

    //重写绘制事件函数
    void paintEvent(QPaintEvent *event) override;

private slots:
    void timeout_slot();

private:
    Ui::Widget *ui;

    QTimer* timer1;  //定义一个定时器类的指针
    quint8 hour;
    quint8 minute;
    quint8 second;

    int cnt;

};
#endif // WIDGET_H

widget.cpp

#include "widget.h"
#include "ui_widget.h"
#include<cmath>

Widget::Widget(QWidget *parent)
    : QWidget(parent)
    , ui(new Ui::Widget)
{
    ui->setupUi(this);
    this->setFixedSize(800,800);
    this->cnt=0;

    QTime timer = QTime::currentTime(); //获取时间
//        QString t = timer.toString("HH:mm:ss A"); //转换为字符串
    QString t = timer.toString("HH:mm:ss"); //转换为字符串
    QStringList tlist = t.split(':');   //以:分割t
//        for(int i=0;i<tlist.size();i++)
//            qDebug() << tlist[i];
    hour    = tlist[0].toUInt();
    minute  = tlist[1].toUInt();
    second  = tlist[2].toUInt();


    timer1 = new QTimer(this);//给定时器类指针实例化对象
    timer1->start(1000);
    //将定时器类对象的timeout信号与自定义的槽函数进行连接
    connect(timer1,&QTimer::timeout,this,&Widget::timeout_slot);

}

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

//重写绘制时间函数
void Widget::paintEvent(QPaintEvent *event)
{

    //    qDebug() << "***************";    //界面发生变化时调用
    QPainter painter(this);
    painter.setPen(QColor("blue"));    //给画家准备画笔
    painter.setFont(QFont("黑体",24));//设置字体

    QBrush brush(QColor("pink"));   //设置刷子——>设置填充色
    painter.setBrush(brush);

    QPen pen;

    //画园
    painter.translate(this->width()/2,this->height()/2);
    painter.drawEllipse(QPoint(0,0),300,300);
    //    painter.drawEllipse(QPoint(400,400),350,350);

    //画刻度 分
    for(int i=0;i<60;i++){
        pen.setColor(QColor("blue"));
        pen.setWidth(1);
        painter.setPen(pen);
        painter.drawLine(QPoint(0,300),QPoint(0,290));
        painter.rotate(6);
    }
    //画刻度 时
    for(int i=0;i<12;i++){
        pen.setColor(QColor("blue"));
        pen.setWidth(3);
        painter.setPen(pen);
        painter.drawLine(QPoint(0,300),QPoint(0,280));
        painter.rotate(30);
    }

    QPainter painterH(this);
    painterH.translate(this->width()/2,this->height()/2);
    pen.setColor(QColor("red"));
    pen.setWidth(6);
    painterH.setPen(pen);
    painterH.rotate(hour*30+(minute/60)*30+second/3600*30);
    painterH.drawLine(0,0,0,-30);

    QPainter painterM(this);
    painterM.translate(this->width()/2,this->height()/2);
    pen.setColor(QColor("green"));
    pen.setWidth(4);
    painterM.setPen(pen);
    painterM.rotate(minute*6+second/60*6);
    painterM.drawLine(0,0,0,-60);

    QPainter painterS(this);
    painterS.translate(this->width()/2,this->height()/2);
    pen.setColor(QColor("blue"));
    pen.setWidth(2);
    painterS.setPen(pen);
    painterS.rotate(second*6);
    painterS.drawLine(0,0,0,-90);

}

void Widget::timeout_slot(){

    QTime timer = QTime::currentTime(); //获取时间
//        QString t = timer.toString("HH:mm:ss A"); //转换为字符串
    QString t = timer.toString("HH:mm:ss"); //转换为字符串
    QStringList tlist = t.split(':');   //以:分割t
//        for(int i=0;i<tlist.size();i++)
//            qDebug() << tlist[i];
    hour    = tlist[0].toUInt();
    minute  = tlist[1].toUInt();
    second  = tlist[2].toUInt();
    qDebug() << hour << ':' << minute << ':' << second;

    update();
    QPaintEvent* q = nullptr;
    this->paintEvent(q);
    this->cnt++;
    qDebug()<<this->cnt;

}

代码实现结果：