why my custom signal not call the custom slot ?

Qt embedded developer

i have made custom signal and slot below way :

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

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

    void errorcodevalue ();

signals:
   void mySignal(int myParameter);

private slots:
    void on_send_button_clicked();

    void on_pushButton_clicked();

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

definition of this signal slot added in below file :

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QDebug>

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

    connect(this, SIGNAL(mySignal()), this, SLOT(on_send_button_clicked));
}

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

void MainWindow::errorcodevalue()
{
    int i = 0;
    if(i==0)
    emit mySignal(i);
    else
        qDebug()<<"signal call failed";
}

void MainWindow::on_send_button_clicked()
{
    qDebug()<<"signal call success";
}


void MainWindow::on_pushButton_clicked()
{
errorcodevalue();
}

so can any body tell me why my custom signal not get emitted on click on pushbutton of ui ?

why my slot also not get called ?

what change can make it work ?

JoeCFD

connect(this, SIGNAL(mySignal()), this, SLOT(on_send_button_clicked() ));
but you can use lambda function for this;
connect( this, &MainWindow::mySignal, this, &MainWindow::on_send_button_clicked );

Qt embedded developer

@JoeCFD said in why my custom signal not call the custom slot ?:

connect( this, &MainWindow::mySignal, this, &MainWindow::on_send_button_clicked );

Dear @JoeCFD ,

your first solution not works for me but second solution works fine. can you tell me why first solution not working ?

mpergand

@Qt-embedded-developer
A little bit of coherence should solve your issue.

you declare your signal with a parameter but not in connect:
connect(this, SIGNAL(mySignal()), this, SLOT(on_send_button_clicked));

your slot has no parameter anyway, should work if adding parenthesis
SLOT(on_send_button_clicked () ));

Look at the console, i'm sure there are connection errors messages.

One would recomand you to use new syntax for connections instead.
Doesn't resolve your logic errors anyway :)

Qt embedded developer

@mpergand said in why my custom signal not call the custom slot ?:

SLOT(on_send_button_clicked () ));

dear i have added below line but its not working

 connect(this, SIGNAL(mySignal()), this, SLOT(on_send_button_clicked () ));

i am getting below warning :
while code runs:

QMetaObject::connectSlotsByName: No matching signal for on_send_button_clicked()
QObject::connect: No such signal MainWindow::mySignal() in ../customsignalchange/mainwindow.cpp:17
QObject::connect: (sender name: 'MainWindow')
QObject::connect: (receiver name: 'MainWindow')

mpergand

@Qt-embedded-developer said in why my custom signal not call the custom slot ?:
connect(this, SIGNAL(mySignal(int)), this, SLOT(on_send_button_clicked () ));

JonB

@Qt-embedded-developer
Why do you not use New Signal Slot Syntax? You would be doing yourself a favour. It is now a decade old anyway, and would prevent the problems you are having with SIGNAL/SLOT() macros.