Q_OBJECT 重要性

编写一个电子时钟demo，发现槽函数不存在，原因是没有在类的开头添加Q_OBJECT宏

#ifndef DIGICLOCK_H
#define DIGICLOCK_H
#include <QLCDNumber>

class DigiClock : public QLCDNumber
{
    //Q_OBJECT
public:
    DigiClock();

    void mousePressEvent(QMouseEvent *);
    void mouseMoveEvent(QMouseEvent *);

public slots:
    void slotshowTime();

private:
    QPoint dragPosition; //保存鼠标点相对电子时钟窗体左上角的偏移值

    bool showColon;//用于显示时间时是否显示：
    QTimer *timer;
};

#endif // DIGICLOCK_H

#include "digiclock.h"
#include <QTime>
#include <QTimer>
#include <QMouseEvent>

DigiClock::DigiClock()
{
    QPalette p = palette();
    p.setColor(QPalette::Window, Qt::blue);
    setPalette(p);;
    setWindowFlags(Qt::FramelessWindowHint);
    setWindowOpacity(0.5);

    timer = new QTimer(this);
    connect(timer, SIGNAL(timeout()), this, SLOT(slotshowTime()));

    timer->start(1000);
    slotshowTime();

    resize(150,60);
    showColon = true;
}

void DigiClock::slotshowTime()
{
    QTime time = QTime::currentTime();
    QString text = time.toString("hh:mm");
    if(showColon)
    {
        text[2] = ':';
        showColon = false;
    }
    else
    {
        text[2] = ' ';
        showColon = true;
    }
    display(text);
}


void DigiClock::mousePressEvent(QMouseEvent * event)
{
    if(event->button()  == Qt::LeftButton)
    {
        dragPosition = event->globalPos()-frameGeometry().topLeft();
        event->accept();
    }
    if(event->button() == Qt::RightButton)
    {
        close();
    }
}

void DigiClock::mouseMoveEvent(QMouseEvent * event)
{
    if(event->buttons() & Qt::LeftButton)
    {
        move(event->globalPos()-dragPosition);
        event->accept();
    }
}

 解决 办法是添加Q_OBJECT宏

没有Q_OBJECT  ，类中的slots,   signal, emit 等都不会被解析；