I'm lost with signals and slots

jenya7

On a sender side
sys.h

#ifndef SYS_H
#define SYS_H

#include <QObject>

class sys : public QObject
{
    Q_OBJECT

    public:
    sys();

    signals:
    void SendMessage(QString msg);

    private:
    void SysParamInit(void);

    public:
    void Print(QString msg);
};

#endif // SYS_H

sys.cpp

#include "sys.h"

sys::sys()
{
}

void sys::Print(QString msg)
{
    emit(SendMessage(msg));
}

on a receiver side
mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

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

public slots:
    void DisplayTerminalMessage(QString msg);

private:
    Ui::MainWindow *ui;
};

#endif // MAINWINDOW_H

mainwindow.cpp

void MainWindow::DisplayTerminalMessage(QString msg)
{
    ui->textEditTerminalRx->setText(msg);
}

and finally

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

    sys system;

    QObject::connect(&system, SIGNAL(SendMessage(QString msg)), &w, SLOT(DisplayTerminalMessage(QString msg));

    system.Print("Hello");

    return a.exec();
}

But I don't see "Hello" in textEditTerminalRx.

J.Hilk

@jenya7
hi, a couple of points

first of, your sender is derived from QObject so at the very least initialize the base class properly

you should use the new qt5 syntax not the old one

QObject::connect(&system, &sys::SendMessage, &w, &MainWindow::DisplayTerminalMessage);

if you want to use the old syntax, do not name your arguments

QObject::connect(&system, SIGNAL(SendMessage(QString)), &w, SLOT(DisplayTerminalMessage(QString));

You should have gotten a runtime warning that your connect failed to establish.

jenya7

@J-Hilk said in I'm lost with signals and slots:

@jenya7
hi, a couple of points

first of, your sender is derived from QObject so at the very least initialize the base class properly

you should use the new qt5 syntax not the old one

QObject::connect(&system, &sys::SendMessage, &w, &MainWindow::DisplayTerminalMessage);

if you want to use the old syntax, do not name your arguments

QObject::connect(&system, SIGNAL(SendMessage(QString)), &w, SLOT(DisplayTerminalMessage(QString));

You should have gotten a runtime warning that your connect failed to establish.

Thank you.
This way
QObject::connect(&system, &sys::SendMessage, &w, &MainWindow::DisplayTerminalMessage);
it works.

first of, your sender is derived from QObject so at the very least initialize the base class properly - how do I do that?

J.Hilk

@jenya7 said in I'm lost with signals and slots:

first of, your sender is derived from QObject so at the very least initialize the base class properly - how do I do that?

Usually you give your constructor a QObject argument and forward that to the Baseclass constructor.

public:
    sys(QObject *parent = nullptr);
//.cpp
sys::sys(QObject parent) : QObject(parent)
{
}

jenya7

Thank you.