Example SLOT/SIGNAL between two object QT - c++

Question

My app, consists in 2 different object (QObject and QMainWIndow), and I am wondering how to communicate between them with SLOT/SIGNAL. Moreover, does existing better approach ?
Can someone make an simple example ? Thank :)
sample
mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include "ui_mainwindow.h"
#include "object.h"
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
private:
Ui::MainWindow *ui;
private slots:
};
#endif // MAINWINDOW_H
mainwindow.cpp
#include "mainwindow.h"
#include "object.h"
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
connect(ui->chkState, SIGNAL(clicked()), this, SLOT(object->chkState();));
}
MainWindow::~MainWindow()
{
delete ui;
}
object.h
#ifndef OBJET_H
#define OBJET_H
#include "mainwindow.h"
#include <QMainWindow>
#include <QObject>
class Object : public QObject
{
Q_OBJECT
public:
explicit Object(QObject *parent = 0);
bool state;
signals:
private slots:
void chkState(Ui::MainWindow *ui);
};
#endif // OBJET_H
objet.cpp
#include "object.h"
#include "mainwindow.h"
Object::Object(QObject *parent) : QObject(parent)
{
}
void Object::chkState(Ui::MainWindow *ui)
{
if (ui->chkState->isChecked())
{
ui->state->setText("true");
state = true;
}
else
{
ui->state->setText("false");
state = false;
}
}

Answer 1

Here is a simple example of how to emit signals and slots.
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include "object.h"
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
signals:
void transmit_to_object(bool value);
private slots:
void receive_from_object(bool value);
void on_checkBox_clicked();
private:
Ui::MainWindow *ui;
object m_object;
};
#endif // MAINWINDOW_H
#ifndef OBJECT_H
#define OBJECT_H
#include <QObject>
class object : public QObject
{
Q_OBJECT
public:
explicit object(QObject * parent = 0);
signals:
void transmit_to_gui(bool value);
private slots:
void receive_from_gui(bool value);
private:
bool state;
};
#endif // OBJECT_H
#include "mainwindow.h"
#include <QApplication>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}
#include "mainwindow.h"
#include "ui_mainwindow.h"
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
connect(&m_object,SIGNAL(transmit_to_gui(bool)),this,SLOT(receive_from_object(bool)));
connect(this,SIGNAL(transmit_to_object(bool)),&m_object,SLOT(receive_from_gui(bool)));
}
MainWindow::~MainWindow()
{
delete ui;
}
void MainWindow::receive_from_object(bool value)
{
if(value)
{
ui->lineEdit->setText("true");
}
else
{
ui->lineEdit->setText("false");
}
}
void MainWindow::on_checkBox_clicked()
{
if(ui->checkBox->isChecked())
{
emit transmit_to_object(true);
}
else
{
emit transmit_to_object(false);
}
}
#include "object.h"
#include "mainwindow.h"
object::object(QObject *parent)
{
}
void object::receive_from_gui(bool value)
{
state = value;
emit transmit_to_gui(state);
}

Answer 2

There are several errors in your code.
First:
connect(ui->chkState, SIGNAL(clicked()), this, SLOT(object->chkState();));
Here you say:
"when we click on the ui->chkState, I want you call a function in this, which is the object->chkState slot". That's definitly not what you want.
What is object ? this object hasn't been created. What you want is :
connect(ui->chkState, SIGNAL(clicked()), myobject, SLOT(chkState()));
with myobject an object of type Object so you need to add in your mainwindow.h a
Object *myobject;
and in your mainwindow.cpp before the connect:
myobject = new Object(this);
Moreover, your function void chkState(Ui::MainWindow *ui); won't work because you cannot get the mainwindow ui in parameter like that.
What I advise you to do, if it's only for tests so you know that parent is the type of MainWindow, you can do:
void Object::chkState()
{
MainWindow* parent = static_cast<MainWindow*>(parent());
if (parent->ui->chkState->isChecked())
{
parent->ui->state->setText("true");
state = true;
}
else
{
parent->ui->state->setText("false");
state = false;
}
}
So the parameter in your slot is removed.