《QT学习之路2》笔记

5.自定义信号槽

之newspaper and reader：

程序如下，完全按照书编写只是稍稍改了一下使得能够显示读者名字。

---------------------------------------------------------

main.cpp

---------------------------------------------------------

#include <QCoreApplication>

#include "newspaper.h"

#include"reader.h"

int main(int argc, char *argv[])

{

    QCoreApplication a(argc, argv);

    Newspaper newspaper("Newspaper A");

    Reader reader("ChenShaoBo");

    QObject::connect(

    &newspaper,

    &Newspaper::newsPaper,

    &reader,

    &Reader::receiveNewspaper);

    newspaper.send();

    return a.exec();

}

----------------------------------------------------------------------

----------------------------------------------------------------------

newspaper.h

---------------------------------------------------------------------

#ifndef NEWSPAPER_H

#define NEWSPAPER_H

#include <QObject>

class Newspaper:public QObject

{

    Q_OBJECT

    public:

    Newspaper(const QString & name):m_name(name) {}

    void send()

    {

        emit newsPaper(m_name);

    }

    signals:

    void newsPaper(const QString &name);

    private:

        QString m_name;

};

#endif // NEWSPAPER_H

--------------------------------------------------------------------------------

---------------------------------------------------------------------------------

reader.h

-------------------------------------------------------------------------------------

#ifndef READER_H

#define READER_H

#include<QObject>

#include<QDebug>

class Reader:public QObject

{

    Q_OBJECT

    public:

    Reader(QString n): Rname(n) {}

    void receiveNewspaper(const QString &name)

    {

    qDebug()<<Rname<<"RECEIVES NWESPAPER:"<<name;

    }

    private:

    QString Rname; //添加读者名字Rname

};

#endif // READER_H

--------------------------------------------------------------------------------------------------

运行结果：

/home/csb/code/c++/qt/17/17 启动中...


"ChenShaoBo" RECEIVES NWESPAPER: "Newspaper A"




-------------------------------------------------------------------------------------

问题1：

关于Q_OBJECT:

通过对该字串的追踪，发现是一个宏定义：

#define Q_OBJECT \

public: \

    Q_OBJECT_CHECK \

    static const QMetaObject staticMetaObject; \

    virtual const QMetaObject *metaObject() const; \

    virtual void *qt_metacast(const char *); \

    QT_TR_FUNCTIONS \

    virtual int qt_metacall(QMetaObject::Call, int, void **); \

private: \

    Q_DECL_HIDDEN_STATIC_METACALL static void qt_static_metacall(QObject *, QMetaObject::Call, int, void **); \

    struct QPrivateSignal {};

这是每一个QT中的对象都必需包含的成员吗？？？

问题2：emit newsPaper(m_name); //当对象改变其状态时，信号就由该对象发射 (emit) 出去，

也就是说emit就是自动触发发送signal的。