Using QSignalMapper instead of Signals and slots

Kushan

In my Qt c++ application I have 3 classes namely MainWindow.cpp, Dialog.cpp and Dialog2.cpp! Currently I am taking a variable value from a QlineEdit iin MainWindow.ui and sending it to Dialog2.cpp through Dialog.cpp using singal slot mechanism!

following is my code

MainWindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
Q_OBJECT

public:
QString value;
explicit MainWindow(QWidget *parent = 0);
~MainWindow();

signals:
void sendValue(QString val);

private slots:
void on_pushButton_clicked();

private:
Ui::MainWindow *ui;
};

MainWindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "dialog.h"

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

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

void MainWindow::on_pushButton_clicked()
{
value=ui->line_Edit->text();
Dialog dialog1;
connect(this,SIGNAL(sendValue(QString)),&dialog1,SLOT(receiveValue(QString)));
emit sendValue(value);
}

Dialog.h
#ifndef DIALOG_H
#define DIALOG_H

#include <QDialog>

namespace Ui {
class Dialog;
}

class Dialog : public QDialog
{
Q_OBJECT

public:
QString value;
explicit Dialog(QWidget *parent = 0);
~Dialog();

private slots:
void receiveValue(QString val)
void on_pushButton_clicked();

signals:
void sendValue2(QString val);

private:
Ui::Dialog *ui;
};

#endif // DIALOG_H

Dialog.cpp
#include "dialog2.h"
#include "dialog.h"
#include "ui_dialog.h"

Dialog::Dialog(QWidget *parent) :
QDialog(parent),
ui(new Ui::Dialog)
{
ui->setupUi(this);
}

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

void Dialog::receiveValue(QString val)
{
value=val;

}

void Dialog::on_pushButton_clicked()
{
Dialog2 dialog2;
connect(this,SIGNAL(sendValue2(QString)),&dialog2,SLOT(receiveValue2(QString)));
emit sendValue2(value);

}

Dailog2.h
#ifndef DIALOG2_H
#define DIALOG2_H

#include <QDialog>

namespace Ui {
class Dialog2;
}

class Dialog2 : public QDialog
{
Q_OBJECT

private slots:
void receiveValue2 (QString val)

public:
QString Value
explicit Dialog2(QWidget *parent = 0);
~Dialog2();

private:
Ui::Dialog2 *ui;
};

#endif // DIALOG2_H

Dialog2.cpp
#include "dialog2.h"
#include "ui_dialog2.h"

Dialog2::Dialog2(QWidget *parent) :
QDialog(parent),
ui(new Ui::Dialog2)
{
ui->setupUi(this);
}

Dialog2::~Dialog2()
{
delete ui;
}

void Dialog2::receiveValue2(QString val){
Value=val;

}

How can I directly send from MianWindow.cpp to Dialog2.cpp using the QSignalMapper?

jsulm

@Kushan For such a use case I don't see any need for QSignalMapper. Why do you want to use it?
"How can I directly send from MianWindow.cpp to Dialog2.cpp using the QSignalMapper?" - what do you mean by "directly". You are already sending from MainWindow to Dialog2. You could even skip the whole signal/slot here and pass the parameter either to Dialog2 constructor or add a public setter method to Dialog2 to set the value.
Signals/Slots are usually used for loose coupling: if sender and receiver do not need to know anything about each other. For example, a QPushButton does not care who is doing something if it is pressed: it just emits the signals and who ever wants to know about this signal connects a slot to it.

Kushan

@jsulm How can I set a public setter method in Dialog2 to receive the value from MainWindow?

jsulm

@Kushan Simple C++:

class Dialog2 : public QDialog
{
Q_OBJECT

private slots:
void receiveValue2 (QString val)

public:
QString Value
explicit Dialog2(QWidget *parent = 0);
~Dialog2();
void setValue(const QString &val) { Value=val; }

private:
Ui::Dialog2 *ui;
};
...
void MainWindow::on_pushButton_clicked()
{
    value=ui->line_Edit->text();
    Dialog dialog1;
    dialog1.setValue(value);
}