QT使用事件事件和绘制事件实现简易时钟

        这个时钟实现的底层原理主要是利用 Qt 的绘图机制和定时器。首先，设置固定大小的窗口，创建定时器并连接到槽函数，定时器每秒钟触发一次，触发窗口重绘。在paintEvent函数中，使用QPainter进行绘图，绘制圆形表盘和时间点标记。通过获取当前时间，计算时针、分针和秒针的旋转角度，使用rotate函数旋转坐标系，然后绘制相应长度的直线代表指针。每次定时器触发时，调用update函数引发重绘，实现时钟的动态显示。

widght.h

#ifndef WIDGET_H
#define WIDGET_H#include <QWidget>
#include <QDebug>
#include <QLabel>
#include <QPen>
#include <QPainter>
#include <QPaintEvent>
#include <QTime>
#include <QTimer>QT_BEGIN_NAMESPACE
namespace Ui { class Widget; }
QT_END_NAMESPACEclass Widget : public QWidget
{Q_OBJECTpublic:Widget(QWidget *parent = nullptr);~Widget();private:Ui::Widget *ui;//定时器QTimer *timer;//绘制事件void paintEvent(QPaintEvent *event) override;private slots:;void update_slot();
};
#endif // WIDGET_H

widget.cpp

#include "widget.h"
#include "ui_widget.h"#include <QTime>
#include <QPainter>Widget::Widget(QWidget *parent): QWidget(parent), ui(new Ui::Widget)
{ui->setupUi(this);// 设置窗口大小this->setFixedSize(600, 600);// 创建定时器timer = new QTimer(this);// 连接定时器时信号与槽函数connect(timer, &QTimer::timeout, this, &Widget::update_slot);timer->start(1000);QLabel *name = new QLabel(this);name->setText("江诗丹顿");name->move(this->width()/2-30,this->height()/2+100);name->setStyleSheet("color: red; font-size: 16px;");}Widget::~Widget()
{delete ui;
}void Widget::paintEvent(QPaintEvent *event)
{Q_UNUSED(event);// 获取当前时间QTime time = QTime::currentTime();// 准备画笔QPen pen;pen.setColor("green");pen.setWidth(2);// 实例化一个画家QPainter painter(this);painter.setPen(pen);painter.drawEllipse(this->width()/2 - 200, this->height()/2 - 200, 400, 400);// 设置坐标系起点为窗口中心painter.translate(this->width()/2, this->height()/2);// 绘制时间点标记pen.setColor("gray");pen.setWidth(2);painter.setPen(pen);for (int i = 0; i < 12; ++i) {painter.save();painter.rotate(30 * i);painter.drawLine(180, 0, 190, 0);painter.restore();}// 绘制时针painter.rotate(30.0 * ((time.hour() % 12) + time.minute() / 60.0 + time.second() / 3600.0));pen.setWidth(8);pen.setColor("blue");painter.setPen(pen);painter.drawLine(0, 0, 50, 0);// 绘制分针painter.rotate(6.0 * (time.minute() + time.second() / 60.0));pen.setWidth(4);pen.setColor("orange");painter.setPen(pen);painter.drawLine(0, 0, 70, 0);// 绘制秒针painter.rotate(6.0 * time.second());pen.setWidth(2);pen.setColor("red");painter.setPen(pen);painter.drawLine(0, 0, 90, 0);}void Widget::update_slot()
{update();
}