一、绘制时钟

widget.h:

#ifndef WIDGET_H
#define WIDGET_H#include <QWidget>
#include <QPainter>
#include <QPaintEvent>
#include <QRectF>
#include <QTimer>
#include <QTime>
#include <QTimerEvent>
#include <QLabel>QT_BEGIN_NAMESPACE
namespace Ui { class Widget; }
QT_END_NAMESPACEclass Widget : public QWidget
{Q_OBJECTpublic:Widget(QWidget *parent = nullptr);~Widget();void paintEvent(QPaintEvent *event) override;
//    void timerEvent(QTimerEvent *e) override;public slots:void timer_slot();private:Ui::Widget *ui;//    int timer_id;        //定义一个定时器idQTimer * timer;int hour;int minute;int second;QLabel *label;
};
#endif // WIDGET_H

widget.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);timer->start(1000);connect(timer,&QTimer::timeout,this,&Widget::timer_slot);}
Widget::~Widget()
{delete ui;
}void Widget::paintEvent(QPaintEvent *event)
{//QRectF rectangle(this->width()/2-200,this->height()/2-200,400,400);QPainter painter(this);painter.setRenderHint(QPainter::Antialiasing);//painter.drawEllipse(rectangle);QPen pen;pen.setStyle(Qt::SolidLine);pen.setColor(QColor("Black"));pen.setWidth(5);painter.setPen(pen);painter.translate(this->width()/2,this->height()/2);painter.drawEllipse(QPoint(0,0),250,250);int i=12;while(i--){painter.rotate(30);painter.drawLine(0,220,0,250);}int j=60;while(j--){painter.rotate(6);painter.drawLine(0,240,0,250);}painter.rotate(180);painter.save();pen.setWidth(8);pen.setColor(QColor("red"));painter.setPen(pen);painter.rotate(30*hour+0.5*minute+0.5/60*second);painter.drawLine(0,0,0,50);painter.restore();painter.save();pen.setWidth(5);pen.setColor(QColor("blue"));painter.setPen(pen);painter.rotate(6*minute+0.1*second);painter.drawLine(0,0,0,90);painter.restore();painter.save();pen.setWidth(1);pen.setColor(QColor("green"));painter.setPen(pen);painter.rotate(6*second);painter.drawLine(0,0,0,150);painter.restore();}void Widget::timer_slot()
{/*this->label->resize(200,100);this->label->move(this->width()-100,this->height()+150);*/QTime sys_t = QTime::currentTime();     //获得系统时间this->hour=sys_t.hour();this->minute=sys_t.minute();this->second=sys_t.second();update();/*//将QTime类对象转换为字符串QString t1 = sys_t.toString("hh:mm:ss");//展示this->label->setText(t1);*/
}

main.cpp:

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