qt完成时钟：

 头文件：

#ifndef WIDGET_H
#define WIDGET_H#include <QWidget>
#include <QPaintEvent>
#include <QtDebug>
#include <QPainter>
#include <QTimerEvent>
#include <QTime>QT_BEGIN_NAMESPACE
namespace Ui { class Widget; }
QT_END_NAMESPACEclass Widget : public QWidget
{Q_OBJECTpublic:Widget(QWidget *parent = nullptr);~Widget();void timerEvent(QTimerEvent *e) override;void paintEvent(QPaintEvent *event) override;private:Ui::Widget *ui;int timer_id;
};
#endif // WIDGET_H

功能函数：

#include "widget.h"
#include "ui_widget.h"Widget::Widget(QWidget *parent): QWidget(parent), ui(new Ui::Widget)
{ui->setupUi(this);// 构造定时器，设置超时为 1 秒timer_id = this->startTimer(1000);
}Widget::~Widget()
{delete ui;
}void Widget::timerEvent(QTimerEvent *e)
{if(e->timerId()==timer_id){QTime sys_t=QTime::currentTime();QString h=sys_t.toString("hh");QString m=sys_t.toString("mm");QString s=sys_t.toString("ss");ui->label->setText(h);ui->label_2->setText(m);ui->label_3->setText(s);}
}void Widget::paintEvent(QPaintEvent *event)
{QPainter painter(this);QPen pen;pen.setColor(QColor("black"));pen.setStyle(Qt::SolidLine);pen.setWidth(5);painter.setPen(pen);painter.translate(this->width()/2,this->height()/2);painter.rotate(0);painter.setBrush(QBrush(QColor("skyblue")));painter.drawEllipse(QPoint(0,0),100,100);for(int i=0;i<360;i+=30){painter.rotate(30);painter.drawLine(QPoint(0,-100),QPoint(0,-90));}for(int i=0;i<360;i+=6){painter.rotate(6);painter.drawLine(QPoint(0,-100),QPoint(0,-95));}//绘制时针painter.save();    // 保存当前的绘制状态// 将绘制的坐标原点移动到表盘的中心int h=ui->label->text().toInt();    // 获取当前的小时int m=ui->label_2->text().toInt();     // 获取当前的分钟double hourAngle = (h%12 + m/60.0)*30.0;  // 计算时针的角度，考虑分钟对时针的影响painter.rotate(hourAngle);    // 旋转坐标系，使时针指向正确的位置painter.setPen(QPen(Qt::black,5));    //设置笔painter.drawLine(QPoint(0,0),QPoint(0,-30));  // 绘制时针，起点是坐标原点 (0, 0)，终点是时针的末端位置painter.restore();       // 恢复之前保存的绘制状态，以便后续绘制//绘制分针painter.save();double minuteAngle = m*6.0;painter.rotate(minuteAngle);painter.setPen(QPen(Qt::red,3));        //设置笔painter.drawLine(QPoint(0,0),QPoint(0,-50));painter.restore();//绘制秒针painter.save();int s=ui->label_3->text().toInt();double secondAngle = s * 6.0;painter.rotate(secondAngle);painter.setPen(QPen(Qt::blue,2));      //设置笔painter.drawLine(QPoint(0,0),QPoint(0,-70));painter.restore();this->update();
}

测试文件：

#include "widget.h"#include <QApplication>int main(int argc, char *argv[])
{QApplication a(argc, argv);Widget w;w.show();return a.exec();
}

 思维导图：