1、实现闹钟

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>
#include <QTime>
#include <QLineEdit>

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 *event);

private slots:
    void on_pushButton_clicked();

private:
    Ui::Widget *ui;
    int id;//定时器id
};
#endif // WIDGET_H

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

Widget::Widget(QWidget *parent)
    : QWidget(parent)
    , ui(new Ui::Widget)
{
    ui->setupUi(this);
    id = startTimer(1000);
}

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

void Widget::timerEvent(QTimerEvent *event)
{
    //获取系统时间
    QTime sys_time = QTime::currentTime();
    //转换为字符串
    QString s = sys_time.toString("hh：mm：ss");
    //将时间设置到ui界面的lab中
    ui->sys_time->setText(s);
    //比较时间
    if(ui->sys_time->text() == ui->clock_lab->text())
    {
        ui->show_lab->setText("R U OK???");
    }
    //居中
    ui->sys_time->setAlignment(Qt::AlignCenter);
}

void Widget::on_pushButton_clicked()
{
    QString s= ui->lineEdit->text();
    ui->clock_lab->setText(s);
}

2、思维导图