QT信号连接信号

有时候代码可能复杂，我们需要一个信号连接另一个信号，比如例子中的下课不是直接运行时触发的，而是点击下课按钮

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "QPushbutton.h"
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    //创建一个老师对象
    this->tc = new Teacher(this);
    //创建一个学生对象
    this->st = new Student(this);
    void(Teacher::*teachersignal2)(void) =  &Teacher::Hungry;
    void(Student::*studentslot2)(void) =  &Student::Treat;
    connect(tc,teachersignal, st, studentslot);
    QPushButton *btn = new QPushButton("下课",this);
    this->resize(600,400);

    connect(tc,teachersignal2, st, studentslot2);
    connect(btn,&QPushButton::clicked,tc,teachersignal2);
}

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

扩展内容

断开信号 使用disconnect(tc,teachersignal2, st, studentslot2);
一个信号可以连接多个槽函数
多个信号可以连接一个槽函数

在teacher类加入一个crying信号

#ifndef TEACHER_H
#define TEACHER_H

#include <QObject>


class Teacher : public QObject
{
    Q_OBJECT
public:
    explicit Teacher(QObject *parent = nullptr);

signals:

  void Hungry();
  void Hungry(QString foodName);
  void Crying();  //老师感动哭了

};
#endif // TEACHER_H
#

  void(Teacher::*teachersignal)(QString) =  &Teacher::Hungry;
    void(Student::*studentslot)(QString) =  &Student::Treat;
    void(Teacher::*teachersignal2)(void) =  &Teacher::Hungry;
    void(Student::*studentslot2)(void) =  &Student::Treat;
    void(Teacher::*teachersignal3)(void) =  &Teacher::Crying;
    connect(tc,teachersignal, st, studentslot);
    //classIsOver();
    QPushButton *btn = new QPushButton("下课",this);
    this->resize(600,400);
    //connect(btn,&QPushButton::clicked,this,&MainWindow::classIsOver);

    connect(tc,teachersignal2, st, studentslot2);
    connect(tc,teachersignal3, st, studentslot2);
    connect(btn,&QPushButton::clicked,tc,teachersignal2);
    connect(btn,&QPushButton::clicked,tc,teachersignal3);

代码中我使用qpushbutton触发了两个信号，同理我也可以使用不同信号触发同一个槽函数

信号和槽函数的参数必须一一对应
信号参数个数可以多余槽的参数个数，但类型要一一对应

Qt4版本以前的信号与槽的连接
连接无参
connect(tc,SIGNAL(Hungry()),st,SLOT(Treat()));
优点，参数直观。缺点，类型不做检测（编译不做检测，运行报错）

Qt5以上支持Qt4的写法，反之不支持。