display is not showing in text box from other class in qt - c++

Question

I have made made a DDisplay class to display my data on gui text box but I have some strange situation, when I call the function from mainwindow class it is working fine but when I try to call the same function from other class it is not working. below is the small code my program
mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <ddisplay.h>
#include <QMainWindow>
#include "test.h"
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
DDisplay b;
Test c;
private slots:
void display(const QString &a);
void on_pushButton_clicked();
private:
Ui::MainWindow *ui;
};
mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
QObject::connect(&b,SIGNAL(display(QString)),this,SLOT(display(QString)));
}
MainWindow::~MainWindow()
{
delete ui;
}
void MainWindow::display(const QString &a){
ui->textBrowser->setText(a);
}
void MainWindow::on_pushButton_clicked()
{
b.printf("hello"); //this function working fine
//c.printf("lllll"); //not working
}
test.h
#ifndef TEST_H
#define TEST_H
#include <QString>
#include <ddisplay.h>
class Test
{
public:
Test();
void printf(const QString &a);
DDisplay b;
};
test.cpp
#include "test.h"
Test::Test()
{
}
void Test::printf(const QString &a){
b.printf(a);
}
ddisplay.h
#include
class DDisplay : public QObject
{
Q_OBJECT
public:
explicit DDisplay(QObject *parent = 0);
void printf(const QString &a);
QString b;
signals:
void display(const QString &a);
public slots:
};
ddisplay.cpp
#include "ddisplay.h"
DDisplay::DDisplay(QObject *parent) :
QObject(parent)
{
}
void DDisplay::printf(const QString &a)
{
b+=a;
emit display(b);
}

Answer 1

c.printf("lllll"); //not working
It's not working because you don't have a connect for this object. DDisplay in Test class is a dfferent instance than that in a MainWindow.
One possible solution for your question in comments below is to connect DDisplay's signal and MainWindow's slot either in main.cpp or in specialized initialization class.