How to access a member function of a cpp file of different class from another class

Question

I am a newbie to QT and C++. I am stuck at a problem where I have two different classes and from B.cpp I want to access a variable of A.cpp. Using debug messages I have seen that the code hits in the setter function but it never sets the value of Textbrowser.

Here is the code of main.cpp.

#include <QApplication>
#include "window.h"
#include "socket.h"

int main(int argc, char **argv)
{
 QApplication app (argc, argv);
 Window *window = new Window();
 Socket *socket = new Socket();

 window->setStyleSheet("background-color: rgb(226, 226, 226);");
 window->showFullScreen();

 return app.exec();
}

Here is window.h

#ifndef WINDOW_H
#define WINDOW_H

#include <QWidget>

class QPushButton;
class QTextBrowser;
class QString;

class Window : public QWidget
{
    Q_OBJECT

public:
    explicit Window(QWidget *parent = 0);

    QPushButton *helloButton;
    QPushButton *exitButton;
    QPushButton *resetButton;
    QTextBrowser *clientMsgWindow;

public slots: 
    void reset();
    void setClientWindow(QString str);
};   
#endif // WINDOW_H

Here is Window.cpp

#include "window.h"
#include <QPushButton>
#include <QTextBrowser>
#include <QDebug>
#include <QString>

Window::Window(QWidget *parent) : QWidget(parent)
{
    /****************** Hello BUTTON ********************/
    helloButton = new QPushButton(this);
    helloButton->setIconSize(QSize(145, 145));
    helloButton->setGeometry(15, 160, 145, 145);
    helloButton->setText("Hello World");

   /******************reset BUTTON ********************/
    resetButton = new QPushButton(this);
    resetButton->setIconSize(QSize(145, 145));
    resetButton->setGeometry(15, 160, 145, 145);
    resetButton->setText("Click to Reset");

    /************* EXIT BUTTON *********************/
    exitButton = new QPushButton(this);
    exitButton->setIcon(QIcon(":/new/prefix1/images/exit.png"));
    exitButton->setIconSize(QSize(145, 145));
    exitButton->setGeometry(635, 10, 145, 145);
    //exitButton->setStyleSheet("background-color: rgb(236, 236, 236);");
    // Signal and slot for EXIT button
    qDebug() << connect(exitButton, SIGNAL (clicked()), this, SLOT (close()));

    /*************** TEXT BROWSER *********************/
    clientMsgWindow = new QTextBrowser(this);
    clientMsgWindow->setMinimumSize(QSize(0,0));
    clientMsgWindow->setMaximumSize(QSize(10000,10000));
    clientMsgWindow->setGeometry(175, 50, 440, 420);
    clientMSgWindow->setStyleSheet("background-color: rgb(236, 236, 236);");
    }

    void Window::setClientWindow(QString Str)
    {
        qDebug() << "Hit in Set client window to set Text";
        qDebug() << Str;
        clientMsgWindow->setText("This is the message from client");
        clientMsgWindow->setText(Str);
        qDebug() << "Setting text done";
     }

/**** Slot to reset the text browser **********/
void Window::reset()
{
    qDebug() << "Process in Reset Window";
    clientMsgWindow->clear();

}

Here is the socket.h

#ifndef SOCKET_H
#define SOCKET_H

#include <QObject>
#include <QDebug>
#include <QTcpServer>
#include <QTcpSocket>

class QTextBrowser;

class Socket : public QObject
{
    Q_OBJECT
public:
    explicit Socket(QObject *parent = 0);
    void setWindow(Window *w);
signals:

public slots:
    void newConnection();

private:
        QTcpServer *server;
        Window *window;
};

#endif // SOCKET_H

Here is the socket.cpp

#include "socket.h"
#include "window.h"
#include <QWidget>
#include <QString>

Socket::Socket(QObject *parent):
    QObject(parent)
{
    server = new QTcpServer(this);
    connect(server, SIGNAL(newConnection()), this, SLOT(newConnection()));  
    if(!server->listen(QHostAddress::QHostAddress("192.168.2.1"), 2793)){
        qDebug() << "SERVER NOT STARTED";
    }
    else{
        qDebug() << "SERVER STARTED";
    }
}
void Socket::setWindow(Window *w)
{
    this->window = w;
}
void Socket::newConnection()
{
    QString clientMsg ;
    QTcpSocket *socket= server->nextPendingConnection();
    socket->write("Server Running on 192.168.2.1");
    socket->flush();
    socket->waitForBytesWritten();

    // Recieve the data from Client
    socket->waitForReadyRead();
    qDebug() << (clientMsg = socket->readAll());

    // Set the Textbrowser clientMsgWindow
    this->window->setClientWindow(clientMsg);
} 

The GUI terminates each time client sends a message.

Answer 1

Instead of creating a new Window instance for every single connection, you should have a single instance. You can make it a singleton, or make it a member of Socket with a setWindow() method, like this:

#ifndef SOCKET_H
#define SOCKET_H

#include <QObject>
#include <QDebug>
#include <QTcpServer>
#include <QTcpSocket>

class QTextBrowser;

class Socket : public QObject
{
    Q_OBJECT
public:
    explicit Socket(QObject *parent = 0);
    void setWindow(Window *w);
signals:

public slots:
    void newConnection();

private:
        QTcpServer *server;
        Window *window;
};

#endif // SOCKET_H

You can even add the window parameter to the constructor, so that you are forced to always set it.

Answer 2

Your design seems to be flawed. When you call

Window* pWindow = new Window();
pWindow->setclientWindow(clientMsg);

in your newConnection method you are creating a new window object and set the text there. However, this is not the same window object you created in your main method, so obviously you won't see the text there. In fact the object you create in the newConnection method is lost forever, since you don't save the pointer anywhere, which will also lead to leaked memory since you can't clean it up. You have to connect your two objects somehow by storing a pointer to the other.

Answer 3

Object::connect: No such slot Socket::Window::setClientWindow()

This error shows that your signal slot parameters are incompatible because setClientWindow takes a QString parameter, and void signal readReady is emitted.

Edit: Following your comment, I see you need to understand basic concepts of signal/slots.

Your connection should be like:

QObject::connect(socket, SIGNAL(readyRead()), window, SLOT(setClientWindow()))

but you don't have a window object to which you can connect socket. You need to refactor your code because it has many design issues.