Qt acess ui of different class - c++

Question

I am trying to access the ui elements of different class but getting error message. I've tried to do this for many hours but still failing, I feel that I am missing something simple.
I am trying to access an element "label" which is in form.h
mainwindow:
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "form.h"
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
Form * elemForm = new Form(this);
elemForm->ui; // works
//elemForm->ui->label; // does not work
}
MainWindow::~MainWindow()
{
delete ui;
}
form.h
#ifndef FORM_H
#define FORM_H
#include <QWidget>
namespace Ui {
class Form;
}
class Form : public QWidget
{
Q_OBJECT
public:
explicit Form(QWidget *parent = 0);
~Form();
Ui::Form *ui;
private:
};
#endif // FORM_H
form.cpp
#include "form.h"
#include "ui_form.h"
Form::Form(QWidget *parent) :
QWidget(parent),
ui(new Ui::Form)
{
ui->setupUi(this);
ui->label; //works fine here
}
Problem is in mainwindow file. I know this is inappropriate code, I'm just interested what I'm doing wrong. I am struggling to find whats wrong, any ideas?

Answer 1

In addition to form.h, you should also include ui_form.h in your MainWindow.h.
That's because the form elements are all defined in Ui::Form which is accessible by including :
#include "ui_form.h"

Answer 2

Please, try to think on what are you doing, and how to do things better.
Don't feel think that method explained by Nejat is controversial to OOP? If you are trying to use OOP, learn how to do it and use it.
To get deeper understanding on what am I talking about, please, read this short story about encapsulation.
Back to your example. Here is clean, simple and easy way to do what you want:
Your mainwindow.h:
#include "mainwindow.h"
#include "ui_mainwindow.h"
// Include only header of your Form, not ui_form.h!
#include "form.h"
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
Form* elemForm = new Form(this);
// Use public method of your Form object!
elemForm->changeUI();
}
Your form.h:
#include <QWidget>
namespace Ui {
class Form;
}
class Form : public QWidget
{
Q_OBJECT
public:
explicit Form(QWidget *parent = 0);
~Form();
void changeUI(); // here you can do all what you want with your UI
private:
Ui::Form *ui;
};
in form.cpp you'll have realization:
void Form::changeUI()
{
ui->... // do all what you want with UI
}