how to call slot of desired class by emitting signal from other class ?

Qt embedded developer

i have written code like below:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QTimer>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

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

QTimer tPolling;

signals:
    void sigPollRequest();

public slots:
    void slotPollTimeout();

private:
    Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H

--------------------
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QDateTime>

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    QObject::connect(&tPolling,&QTimer::timeout,this,&MainWindow::slotPollTimeout);
    tPolling.start(1000);
}

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

void MainWindow::slotPollTimeout()
{
     emit sigPollRequest();
}

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

#ifndef FORM_H
#define FORM_H

#include <QWidget>

namespace Ui {
class Form;
}

class Form : public QWidget
{
    Q_OBJECT

public:
    explicit Form(QWidget *parent = nullptr);
    ~Form();

public slots:
    bool slotPollingRequested();

private:
    Ui::Form *ui;
};

#endif // FORM_H

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

#include "form.h"
#include "mainwindow.h"
#include "ui_form.h"
#include <QDebug>

Form::Form(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Form)
{
    ui->setupUi(this);

    MainWindow *ptr = new(MainWindow);

    QObject::connect(ptr,&MainWindow::sigPollRequest,this,&Form::slotPollingRequested);

}

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

bool Form::slotPollingRequested()
{
   qDebug()<<"hi";
}

here from using timer i am emitting one signal named sigPollRequest . using this signal i want to call slot named slotPollingRequested.

Now when i am running my code my code is emitting signal but it not calls the slot slotPollingRequested.

why its not calling my slot ? what i need to write to resolve this ?

JonB

@Qt-embedded-developer
Make yourself a rule: do not allow yourself to put #include "mainwindow.h" anywhere other than in mainwindow.cpp. No other class/module should know about or be able to reference it. So take that out of form.h/.cpp. That you won't be tempted to do anything about class MainWindow there.

MainWindow creates Form *frm = new Form();, so MainWindow can connect a signal in Form to a slot in MainWindow, or the other way round, like:

connect(form, &Form::signal, this, &MainWindow::slot);
// or
connect(this, &MainWindow::signal, form, &Form::slot);

This should be done in MainWindow class code, not in Form class code.

Christian Ehrlicher

@Qt-embedded-developer said in how to call slot of desired class by emitting signal from other class ?:

MainWindow *ptr = new(MainWindow);

QObject::connect(ptr,&MainWindow::sigPollRequest,this,&Form::slotPollingRequested);

Because you create a new instace of MainWindow instead using the correct one - c++ basics.

Qt embedded developer

@Christian-Ehrlicher

so can you tell me what i need to write ?

because we know that by adding header file we can access the other class function. so can you tell me what mistake i done ? and give guidance that how to resolve with example ?

Christian Ehrlicher

@Qt-embedded-developer said in how to call slot of desired class by emitting signal from other class ?:

and give guidance that how to resolve with example ?

Sorry no - passing a pointer from one class to another is really the basics of c++.

Qt embedded developer

@Christian-Ehrlicher

means i need to create instance of form class into the Mainwindow class and after that this slot get call ?

Christian Ehrlicher

@Qt-embedded-developer said in how to call slot of desired class by emitting signal from other class ?:

means i need to create instance of form class into the Mainwindow class and after that this slot get call ?

You have to create you Form class somewhere yes - how should it be shown and used otherwise?

Qt embedded developer

@Christian-Ehrlicher i have achieved goal. but not the way i want it. it is somewhat different way.

#include "mainwindow.h"

#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec();
}

-----------
#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QTimer>
#include "form.h"

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

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

QTimer tPolling;


signals:
    void sigPollRequest();

public slots:
    void slotPollTimeout();

private:
    Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H

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

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QDateTime>
#include "form.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    Form *frm = new Form();


    QObject::connect(this,SIGNAL(sigPollRequest()),frm,SLOT(slotPollingRequested()));

    QObject::connect(&tPolling,&QTimer::timeout,this,&MainWindow::slotPollTimeout);
    tPolling.start(1000);

}

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

void MainWindow::slotPollTimeout()
{
     emit sigPollRequest();
}

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

#ifndef FORM_H
#define FORM_H

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

namespace Ui {
class Form;
}

class Form : public QWidget
{
    Q_OBJECT

public:
    explicit Form(QWidget *parent = nullptr);
    ~Form();


public slots:
    bool slotPollingRequested();

private:
    Ui::Form *ui;
};

#endif // FORM_H

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

#include "form.h"
#include "mainwindow.h"
#include "ui_form.h"
#include <QDebug>

Form::Form(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Form)
{
    ui->setupUi(this);
}

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

bool Form::slotPollingRequested()
{
   qDebug()<<"hi";
}

But still have confusion that how i can call slot of form class by signal of mainwindow class . ultimately i want to write my connect system call into my form class and want to make it work.

JonB

@Qt-embedded-developer
Make yourself a rule: do not allow yourself to put #include "mainwindow.h" anywhere other than in mainwindow.cpp. No other class/module should know about or be able to reference it. So take that out of form.h/.cpp. That you won't be tempted to do anything about class MainWindow there.

MainWindow creates Form *frm = new Form();, so MainWindow can connect a signal in Form to a slot in MainWindow, or the other way round, like:

connect(form, &Form::signal, this, &MainWindow::slot);
// or
connect(this, &MainWindow::signal, form, &Form::slot);

This should be done in MainWindow class code, not in Form class code.