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Here's the program:

box.h

Quoted

#ifndef BOX_H
#define BOX_H
#include <qmainwindow.h>
#include <qpushbutton.h>

class QPushButton;

class MainWindow : public QMainWindow
{
Q_OBJECT

public:
MainWindow();

private:
QPushButton *button;
};

#endif

box.cpp

Quoted

#include <QtGui>
#include "box.h"

MainWindow::MainWindow()
{
button = new QPushButton("Hello");
}

main.cpp

Quoted

#include "box.h"
#include <QtGui>

int main(int argc,char *argv[])
{
QApplication app(argc,argv);
MainWindow *Wind = new MainWindow;
Wind->show();
return app.exec();
}

And the problem is that the button inside the window does not show (only the mainwindows shows).

Hey.

I did this:

Quoted

MainWindow(QWidget *parent=0);

I'll explain it here and you tell me if I'm right.
So, here I declared a constructor of MainWindow class that has a parameter which is a pointer that points to a type QWidget and it's default value is 0. (that means if I was calling the constructor like this "MainWindow()" it would have set it to 0 (what would it mean if it would have been set to 0 -> that this windows is a parent window)?


And I did this:

Quoted

MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent)

Here I declared a constructor MainWindow to use a pointer to a type QWidget (that gets the value of a parent) ----> and then it passes that value to a QMainWindow constructor. Is that right?

Can I only ask you: which value does it get? --> can you tell me in example?

I mean which value does the pointer get? I understand that, just cannot imagine it... A simple example would help me, thank you

I have another example that will help me understand.

I cannot get this to work properly:


box.h

Quoted

#ifndef BOX_H
#define BOX_H
#include <qmainwindow.h>
#include <qpushbutton.h>

class QPushButton;

class MainWindow : public QMainWindow
{
Q_OBJECT
public:
MainWindow(QWidget *parent=0);
private:
QPushButton *button;
};


class MainWindow2 : public MainWindow
{
Q_OBJECT
public:
MainWindow2(MainWindow *parent2=0);
private:
QPushButton *button2;
};


#endif

box.cpp

Quoted

#include <QtGui>
#include "box.h"

MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent)
{
button = new QPushButton("Hello",this);
}

MainWindow2::MainWindow2(MainWindow *parent2) : MainWindow(parent2)
{
button2 = new QPushButton("Kako_si?",this);
}

main.cpp

Quoted

#include "box.h"
#include <QtGui>

int main(int argc,char *argv[])
{
QApplication app(argc,argv);
MainWindow *Wind = new MainWindow;
Wind->show();
return app.exec();
}