Signals Slots and Class Pointers

[Atomic_Sheep]

Looks like HEADERS in pro are fine.

As for the code...

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
 
#include <QMainWindow>
#include "glwidget.h"
 
namespace Ui {
    class MainWindow;
}
 
class MainWindow : public QMainWindow
{
    Q_OBJECT
 
public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();
 
    int m_Angle;
    void AngleUpdate(int m_Angle);
private:
    Ui::MainWindow *ui;
};
 
#endif // MAINWINDOW_H

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include "glwidget.h"

namespace Ui {
    class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

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

    int m_Angle;
    void AngleUpdate(int m_Angle);
private:
    Ui::MainWindow *ui;
};

#endif // MAINWINDOW_H

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glwidget.h

#ifndef GLWIDGET_H
#define GLWIDGET_H
 
#include <QtOpenGL/QGLWidget>
#include <cmath>
#include "mainwindow.h"
#include <QMessageBox>
 
class GLWidget : public QGLWidget
{
    Q_OBJECT
public:
    explicit GLWidget(QWidget *parent = 0);
 
int m_Angle;
 
 
void initializeGL();
void paintGL();
void resizeGL(int w, int h);
 
public slots:
void SetAngle(int Angle);
 
};
 
#endif // GLWIDGET_H

#ifndef GLWIDGET_H
#define GLWIDGET_H

#include <QtOpenGL/QGLWidget>
#include <cmath>
#include "mainwindow.h"
#include <QMessageBox>

class GLWidget : public QGLWidget
{
    Q_OBJECT
public:
    explicit GLWidget(QWidget *parent = 0);

int m_Angle;


void initializeGL();
void paintGL();
void resizeGL(int w, int h);

public slots:
void SetAngle(int Angle);

};

#endif // GLWIDGET_H

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mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
 
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    connect(ui->horizontalSlider, SIGNAL(valueChanged(int)), ui->Widget, SLOT(SetAngle(int Angle))); //Widget is just the standard widget which I've promoted to GLWidget in form editor
    connect(ui->horizontalSlider, SIGNAL(valueChanged(int)), ui->label, SLOT(setNum(int)));
}
 
MainWindow::~MainWindow()
{
    delete ui;
}

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

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    connect(ui->horizontalSlider, SIGNAL(valueChanged(int)), ui->Widget, SLOT(SetAngle(int Angle))); //Widget is just the standard widget which I've promoted to GLWidget in form editor
    connect(ui->horizontalSlider, SIGNAL(valueChanged(int)), ui->label, SLOT(setNum(int)));
}

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

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glwidget.cpp

#include "glwidget.h"
 
GLWidget::GLWidget(QWidget *parent) :
    QGLWidget(parent)
{
 
}
 
void GLWidget::SetAngle(int Angle)
{
    if (Angle != m_Angle)
    {
        m_Angle = Angle;
        QMessageBox::information(0, "inside slot", "inside slot");
    }
}

#include "glwidget.h"

GLWidget::GLWidget(QWidget *parent) :
    QGLWidget(parent)
{

}

void GLWidget::SetAngle(int Angle)
{
    if (Angle != m_Angle)
    {
        m_Angle = Angle;
        QMessageBox::information(0, "inside slot", "inside slot");
    }
}

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P.S. There might be one or two mistakes here or there e.g. m_Angle used instead of Angle or something like that... I'm 99% sure I don't have that mistake in my actual program.