C++, Qt Signals & slots - c++

Question

I'm trying to understand Qt 4.8 signals and slots so I wrote some code to test it out for myself. Eventually, I want to be able to use a common source file in my project so that serial ports can be accessed from any source file in the project.
I set up a Qt GUI application and added a C++ class header and source file, shown below.
When I try to build, I get the error message when I try to emit the signal.
/home/user/QTProjects/stest1/stest1/ser.cpp:25: error: invalid use of 'this' in non-member function
I haven't even gotten to the stage of setting up the connections yet!
My newbie status is obvious, I'd be grateful for any help.
Thanks,
James
The following is the MainWindow.cpp:-
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "ser.h"
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
ser *j = new ser;
j->init();
connect (this, SIGNAL(click()), ser, SLOT(testprint()));
}
MainWindow::~MainWindow()
{
delete ui;
}
void MainWindow::on_pushButton_clicked()
{
QByteArray ba1;
ba1.resize(6);
ba1[0]='H'; ba1[1]='e'; ba1[2]='l'; ba1[3]='l'; ba1[4]='o'; ba1[5]='\n';
this->printtext(ba1);
}
void MainWindow::printtext(const QByteArray &data)
{
ui->textEdit->insertPlainText(QString(data));
}
The following is the 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 = 0);
~MainWindow();
private slots:
void on_pushButton_clicked();
void printtext(const QByteArray &data);
private:
Ui::MainWindow *ui;
signals:
// void click;
};
#endif // MAINWINDOW_H
The following is ser.cpp:-
#include "ser.h"
#include <QObject>
ser::ser(QObject *parent) :
QObject(parent)
{
}
void ser::init()
{
// connect(this->, SIGNAL(testsignal), MainWindow, SLOT(printtext(const QByteArray &data)));
}
void ser::testprint()
{
QByteArray ba1;
ba1.resize(8);
ba1[0]='S'; ba1[1]= '0'; ba1[2]= ' '; ba1[3]= 'l'; ba1[4]='o'; ba1[5]='n'; ba1[6]='g'; ba1[7]='\n';
emit this->testsignal(ba1);
}
The following is ser.h
#ifndef SER_H
#define SER_H
#include "mainwindow.h"
#include <QObject>
class ser : public QObject
{
Q_OBJECT
public:
explicit ser(QObject *parent = 0);
void init();
signals:
void testsignal(const QByteArray &data);
private slots:
void testprint();
public slots:
};
#endif // SER_H

Answer 1

Your method is implemented as void testprint() { ... }, but it should be void ser::testprint() { ... }. It's in your cpp file.
Also note that you don't need to use this-> to refer to class members. emit testsignal(ba1); will fork fine.

Answer 2

I think should be
connect (this, SIGNAL(click()), j, SLOT(testprint()));
instead of
connect (this, SIGNAL(click()), ser, SLOT(testprint()));
that apart, I can't spot where you connect testsignal

Answer 3

Great, that worked.
connect (this, SIGNAL(click()), j, SLOT(testprint()));
My next problem is connecting the signal in ser to the slot in the MainWindow. I used
connect(j,
SIGNAL(testsignal),
this,
SLOT(printtext(const QByteArray &data)));
It was inserted immediately after the other connect statement.
This does not print out the expected message "Slong". It also does not give me any error! What is the problem?
James