[QT] Implementation of callback function

A callback function is a function you write,Let the pre-written system call.You call system functions,is straight.让系统调用你的函数,就是回调.

A 让 B 做事,根据粒度不同,可以理解成 A 函数调用 B 函数,或者 A 类使用 B 类,或者 A 组件使用 B 组件等等.反正就是 A 叫 B 做事.当 B 做这件事情的时候,Not enough information for your own needs,而 A 又有.就需要 A 从外面传进来,或者 B Do what you do and then apply outside.对于 B 来说,A passive access to information,One is to take the initiative to get information.Some people give both ways a term,It's called pressing of information（ push）,and information pull（ pull）.

1、callback.h

#ifndef CALLBACK_H
#define CALLBACK_H

/*A 让 B 排序,B 会做排序,But sorting needs to know which is bigger than which, * 这点 B 自己不知道,就需要 A 告诉它.And judging the size itself is an act, * 既然 C A function that cannot be passed a first value in the language,It is designed to pass a function pointer of the second value, * This function pointer is A 传向 B 的信息,Used to describe the behavior of judging size. * 这里本来 A 调用 B 的,结果 B 又调用了 A information to tell it,也就是 callback */

#include <QWidget>

typedef double(*cbFunc)(double,double);      //函数指针

class CallBack : public QWidget
{
    
    Q_OBJECT
public:
    explicit CallBack(QWidget *parent = nullptr);

    void m_getData(cbFunc);       //调用回调函数

signals:

public slots:
};

#endif // CALLBACK_H

2、callback.cpp

#pragma execution_character_set("utf-8")
#include "callback.h"
#include <QDebug>

CallBack::CallBack(QWidget *parent) : QWidget(parent)
{
    

}

void CallBack::m_getData(cbFunc m_cbFunc)
{
    
    double i = m_cbFunc(3.6,5.7);
    qDebug() << "The value returned by the callback function: " << i;
}

3、widget.h

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>
#include "callback.h"

class Widget : public QWidget
{
    
    Q_OBJECT

public:
    Widget(QWidget *parent = nullptr);
    ~Widget();

    CallBack m_callback;

    static double m_getPosition(double a, double b);

};

#endif // WIDGET_H

4、widget.cpp

#pragma execution_character_set("utf-8")
#include "widget.h"
#include <QDebug>

Widget::Widget(QWidget *parent)
    : QWidget(parent)
{
    
    //Pass the address of the function to other functions by passing parameters,The function is then called through the function pointer in other functions --回调
    m_callback.m_getData(&m_getPosition);
}

Widget::~Widget()
{
    

}

double Widget::m_getPosition(double a, double b)
{
    
    qDebug() << "The callback function triggers the incoming value: " << a << b;
    return a+b;
}

5、运行结果输出