Can't connect SIGNAL to SLOT in same classe and also two differents classes

jawad_soft

I am developing an QT application under QT5.13, and I am trying to connect a signal with a slot of the same class because the end goal was to connect the signal of this class with the slot of a seconde class but it doesn't work in both cases and so I tried to validate it in the same class before going to the second step.

There is my code :

udpserver.h :

#ifndef UDPSERVER_H
#define UDPSERVER_H

#include <QObject>
#include <QUdpSocket>
#include <QDebug>
#include <QJsonDocument>
#include <QJsonObject>
#include <QJsonArray>

class UDPServer : public QObject
{
    Q_OBJECT

public:
    explicit UDPServer(QObject *parent = nullptr);
    QUdpSocket *getSocket() const;
    void Send(QString d);
    void pMsg(QByteArray App_Msg);

signals:
    void ack_gui(QString ack_msg);

public slots:
    void readyRead();
    void ackRead(QString _ack_msg);

private:
    QUdpSocket *socket;
};

#endif // UDPSERVER_H

udpserver.cpp:

#include "udpserver.h"

UDPServer::UDPServer(QObject *parent) : QObject(parent)
{
    socket = new QUdpSocket(this);
    QTextStream(stdout) << "Socket Server created ! " << endl;
    socket->bind(QHostAddress::LocalHost, QT_SERVER_PORT);

    connect(socket, SIGNAL(readyRead()), this, SLOT(readyRead()));
    connect(socket, SIGNAL(ack_gui(QString)), this, SLOT(ackRead(QString)));
}

QUdpSocket *UDPServer::getSocket() const
{
   return socket;
}

void UDPServer::SendData(QString d)
{
    keyprod prod1;
    QByteArray Data;
    QJsonObject Js_command = prod1.ObjectFromString(d);
    Data.append(d);

    socket->writeDatagram(Data, QHostAddress::LocalHost, PYTHON_SERVER_PORT);
    qDebug() << "catch! " << endl;
}

void UDPServer::pMsg(QByteArray App_Msg)
{
    QJsonDocument JsonDocument = QJsonDocument::fromJson(App_Msg);
    QJsonObject JsonApp_Msg = JsonDocument.object();
    QString Typo = JsonApp_Msg["no"].toString();

    emit ack_gui(Typo);
}

void UDPServer::readyRead()
{

    QByteArray buffer;
    buffer.resize(socket->pendingDatagramSize());
    QHostAddress sender;
    quint16 senderPort;
    socket->readDatagram(buffer.data(), buffer.size(), &sender, &senderPort);
    pMsg(buffer);
}


void UDPServer::ackRead(QString _ack_msg)
{
    qDebug() << "Message : " << _ack_msg;
}

As you can see it is a very classic class nothing very complicated in QT,the first connects works, but the second where I use my personal signal does not work :

connect(socket, SIGNAL(ack_gui(QString)), this, SLOT(ackRead(QString)));

The code are compiled, but when i lunch it, i got this :

QObject::connect: No such signal QUdpSocket::ack_gui(QString) in ../../udpserver.cpp

I also tried the new connect syntax in QT5 but it didn't work.

I know this topic has been touched on several times already but i have already checked these topics and still haven't found a solution can you help me please.

Thank you in advance for your help !

J.Hilk

@jawad_soft
ok we can fix that because client is stack allocated not heap and a local variable,

BUT

thats only fix of the bug here's an underlying bigger issue, client should probably be a class member, because it will be destroyed, as soon as the constructor exits!

The "Fix"

connect(&client, &UDPServer::ack_gui, this, &MainWindow::onLaunchButton);

i Suppose with new syntaxe you can't have slots with same name and differents arguments haha

of course you can thats what qOverload is for :D
https://doc.qt.io/qt-5/qtglobal.html#qOverload

jsulm

@jawad_soft said in Can't connect SIGNAL to SLOT in same classe and also two differents classes:

QObject::connect: No such signal QUdpSocket::ack_gui(QString) in ../../udpserver.cpp

Isn't this error clear? There is no such signal in QUdpSocket.
Don't you want this actually:

connect(this, SIGNAL(ack_gui(QString)), this, SLOT(ackRead(QString)));

raven-worx

@jawad_soft said in Can't connect SIGNAL to SLOT in same classe and also two differents classes:

connect(socket, SIGNAL(ack_gui(QString)), this, SLOT(ackRead(QString)));

QUdpSocket class doesn't have a ack_gui signal.
You might want change socket to this?

Edit: too slow :)

J.Hilk

@jawad_soft said in Can't connect SIGNAL to SLOT in same classe and also two differents classes:

connect(socket, SIGNAL(ack_gui(QString)), this, SLOT(ackRead(QString)));

this
connect(this, SIGNAL(ack_gui(QString)), this, SLOT(ackRead(QString)));

or (better)
connect(this, &UDPServer::ack_gui, this, &UDPServer::ackRead);

JonB

@jawad_soft said in Can't connect SIGNAL to SLOT in same classe and also two differents classes:

I also tried the new connect syntax in QT5 but it didn't work.

As others have said: please change over to the new-style syntax always! No need to ever use SIGNAL/SLOT() macros. If the new-style "doesn't work", at least it's giving you compile-time help on why not, which you must address!

J.Hilk

@JonB said in Can't connect SIGNAL to SLOT in same classe and also two differents classes:

No need to ever use SIGNAL/SLOT() macros

alt text

I have at least 1 use case where the use of old macros is essential 😉
Fringe case, but it exists

JonB

@J-Hilk
Of course I respect your comment/case. However, do you think this is good advice for the OP here? Or do you think he would be better advised not using this as an excuse to stay with old-style but would be better using new-style for all his cases?

J.Hilk

@JonB Fair enough point I'm only objecting to the generalization, there's a reason why you don't get a whole bunch of deprecated warning when you use the old syntax.

Even though you should, in my opinion at least.

jawad_soft

@J-Hilk @raven-worx ! Thanks for reply, effectively it works better, I don't see the connection failure message, but what about the arguments of signal and slot ? :D I will even take the opportunity to use the new syntax.

my goal was to connect the signal ack_gui that i created in this class with the slot of my classe mainwindows class, should i integrate it this way :

mainwindows .h :

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QPushButton>
#include <QApplication>
#include <QDesktopWidget>
#include <QObject>
#include <QWidget>
#include <QLabel>
#include <QTextStream>
#include <QTimer>
#include <QLoggingCategory>
#include <QGraphicsView>
#include <QGraphicsRectItem>
#include <QVariantAnimation>
#include <QGraphicsScene>
#include <QGraphicsProxyWidget>

#include "udpserver.h"


namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

private:

    QColor menuButtonColor;

    Ui::MainWindow *m_ui;
    QPushButton *m_Button;

    void init();

private slots:
    void onLaunchButton(QString ackMsg);
    void onLaunchButton();


protected:
    bool event(QEvent *event) override;

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


public slots:
    void update_data();
};

#endif // MAINWINDOW_H

mainwindows .cpp :

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QFile>
#include <QTextStream>


MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent, Qt::FramelessWindowHint),
    m_ui(new Ui::MainWindow)
{
        UDPServer client;
  
       QObject::connect(m_Button, SIGNAL(clicked()),this, SLOT(onLaunchButton()));
       connect(client.getSocket(), &UDPServer::ack_gui, this, &MainWindow::onLaunchButton(QString));
}

With function client.getSocket() i will get socket private attribut of UDPServer , I feel like I'm going to make the same error again how I refer to the UDP socket class from the class MainWindow ?

Thank you again for your help

J.Hilk

@jawad_soft said in Can't connect SIGNAL to SLOT in same classe and also two differents classes:

With function client.getSocket() i will get socket private attribut of UDPServer , I feel like I'm going to make the same error again how I refer to the UDP socket class from the class MainWindow ?

correct, UDPServer::ack_gui is part of the UDPServer class and your instance of that class is (apparently) simply client therefore:

connect(client, &UDPServer::ack_gui, this, &MainWindow::onLaunchButton);

Edit:
but you have to drop the QString argument, the new syntax does not require / allow that

jawad_soft

@J-Hilk ! Ok , i Suppose with new syntaxe you can't have slots with same name and differents arguments haha !!
I got error when i implement the line :

connect(client, &UDPServer::ack_gui, this, &MainWindow::onLaunchButton);

Errore =>

no matching member function for call to 'connect'

I try to add this :

QObject::connect(client, &UDPServer::ack_gui, this, &MainWindow::onLaunchButton);

But nothing change !?

J.Hilk

@jawad_soft
ok we can fix that because client is stack allocated not heap and a local variable,

BUT

thats only fix of the bug here's an underlying bigger issue, client should probably be a class member, because it will be destroyed, as soon as the constructor exits!

The "Fix"

connect(&client, &UDPServer::ack_gui, this, &MainWindow::onLaunchButton);

i Suppose with new syntaxe you can't have slots with same name and differents arguments haha

of course you can thats what qOverload is for :D
https://doc.qt.io/qt-5/qtglobal.html#qOverload

jawad_soft

@J-Hilk Great explanation ! I solved my problem and at the same time I learned more things.