updating value from mainwindow to dialog - c++

Question

I have a mainwindow that generates random int numbers every second in "numbers" and I have a button that opens a new dialog. In that dialog is a button "Get Number" and a qlabel. If I press "Get Number" I want the current generated number from the mainwindow set to the dialog label text. I tried to write a member function in the mainwindow class that returns the actual value but I cant call it from the dialog and I think that's the wrong way. How can I get this current generated int "numbers" into the dialog? My plain code:
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 generateNumbers();
private:
Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H
mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "dialog.h"
#include <QTimer>
#include <QDebug>
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
QTimer *timer = new QTimer(this);
connect(timer,SIGNAL(timeout()), this, SLOT(generateNumbers()));
timer->start(1000);
}
MainWindow::~MainWindow()
{
delete ui;
}
void MainWindow::on_pushButton_clicked()
{
Dialog dialog;
dialog.setModal(true);
dialog.exec();
}
void MainWindow::generateNumbers()
{
int numbers = qrand() % 100;
qDebug() << numbers;
}
dialog.h
#ifndef DIALOG_H
#define DIALOG_H
#include <QDialog>
namespace Ui {
class Dialog;
}
class Dialog : public QDialog
{
Q_OBJECT
public:
explicit Dialog(QWidget *parent = 0);
~Dialog();
private:
Ui::Dialog *ui;
};
#endif // DIALOG_H
dialog.cpp
#include "dialog.h"
#include "ui_dialog.h"
Dialog::Dialog(QWidget *parent) :
QDialog(parent),
ui(new Ui::Dialog)
{
ui->setupUi(this);
}
Dialog::~Dialog()
{
delete ui;
}

Answer 1

On mainwindow.h, add a signal:
signals:
void update_number(int);
On mainwindow.cpp, emit that signal everytime you generate a new number:
void MainWindow::generateNumbers()
{
int numbers = qrand() % 100;
emit update_number(numbers); // signals that a new number has been generated
qDebug() << numbers;
}
and your on_pushButton_clicked() should look like this:
void MainWindow::on_pushButton_clicked()
{
Dialog dialog(this); // main window as the parent of dialog
dialog.setModal(true);
dialog.exec();
}
On dialog.h, add an attribute called number_ and add the following slot:
public slots:
void on_update_number(int number); // updates the number_
private:
int number_; // it will be updated with the most recent number
Ui::Dialog *ui;
On dialog.cpp, connect the signal to the slot:
Dialog::Dialog(QWidget *parent) :
QDialog(parent),
ui(new Ui::Dialog)
{
ui->setupUi(this);
connect(parent, SIGNAL(update_number(int)), this, SLOT(on_update_number(int)));
}
add the slot code:
void Dialog::on_update_number(int number)
{
number_ = number;
}
Finally, when the user clicks the button "Get Number" in the dialog, set the label text:
void Dialog::on_pushButton_clicked()
{
ui->label->setText(QString::number(number_));
}
For more information on Signals & Slots go here.