制作一个简易圆形时钟

头文件：

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>
#include <QPaintEvent>
#include <QDebug>
#include <QPainter>
#include <QTimerEvent>
#include <QTime>
#include <QThread>
QT_BEGIN_NAMESPACE
namespace Ui { class Widget; }
QT_END_NAMESPACE

class Widget : public QWidget
{
    Q_OBJECT

public:
    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

源文件：

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

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

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

void Widget::paintEvent(QPaintEvent *event)
{
    QPainter painter(this);//创建一个画师对象
       painter.setRenderHint(QPainter::Antialiasing);

       // 将原点移动到窗口中心 (使画布居中)
       painter.translate(width() / 2, height() / 2);

       //放大
       painter.scale(2, 2);

       // 绘制表盘
       painter.setPen(Qt::black);//设置画笔为空。
       painter.setBrush(Qt::white);//设置画刷为白色。
       painter.drawEllipse(-100,-100, 200, 200);
       painter.drawText(-7,-78,"12");
       painter.drawText(78,5,"3");
       painter.drawText(-5,85,"6");
       painter.drawText(-83,5,"9");
       // 绘制刻度
       painter.setPen(Qt::black);//设置画笔为黑色。
       for (int i = 0; i < 12; ++i) {//循环绘制时钟刻度
           painter.drawLine(0, -90, 0, -100);
           painter.rotate(30);
       }
       for (int i = 0; i < 36; ++i) {
           painter.drawLine(0, -95, 0, -100);
           painter.rotate(10);
       }

       // 绘制时针、分针和秒针
       QTime time = QTime::currentTime();//获取当前时间。
       painter.rotate(30.0 * ((time.hour() + time.minute() / 60.0)));
       painter.setPen(Qt::NoPen);
       painter.setBrush(Qt::black);
       // 绘制时针，以多边形方式绘制，坐标点依次为(-2,5)、(2,5)、(0,-80)
       painter.drawPolygon(QPolygonF(QVector<QPointF>() << QPointF(-2, 5)
                                                        << QPointF(2, 5)
                                                        << QPointF(0, -50)));

       painter.rotate(6.0 * (time.minute() + time.second() / 60.0));//60分钟转360度，一分钟转6度
       painter.setBrush(Qt::blue);
       painter.drawPolygon(QPolygonF(QVector<QPointF>() << QPointF(-1, 5)
                                                        << QPointF(1, 5)
                                                        << QPointF(0, -75)));

       painter.rotate(6.0 * time.second());
       painter.setBrush(Qt::red);
       painter.drawPolygon(QPolygonF(QVector<QPointF>() << QPointF(-1, 5)
                                                        << QPointF(1, 5)
                                                        << QPointF(0, -90)));

       this->update();
}

void Widget::timerEvent(QTimerEvent *e)
{
    timer_id=this->startTimer(1000);
}

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();
}

运行结果：

思维导图：