Qt, using OpenGL, QGLWidget is private - c++

Question

I'm quite new to Qt. I wanted to create a simple application where there's triangle generated using OpenGL and three push buttons changing that triangle colour. Unfortunately I get an error:
E:\Programy\Qt\5.3\mingw482_32\include\QtOpenGL\qgl.h:457: error: 'QGLWidget::QGLWidget(const QGLWidget&)' is private
Q_DISABLE_COPY(QGLWidget)
I don't know what to do. Here's my code:
MainWindow.h
class MainWindow : public QMainWindow
{
Q_OBJECT
QVBoxLayout *layout;
public:
MainWindow(QWidget *parent = 0);
~MainWindow();
private:
QPushButton *redButton;
QPushButton *greenButton;
QPushButton *blueButton;
public slots:
void redSlot(Widget w);
void greenSlot(Widget w);
void blueSlot(Widget w);
};
Slots in MainWindow.cpp look like this:
void MainWindow::redSlot(Widget w)
{
w.setColor(red);
}
Widget.h
class Widget : public QGLWidget
{
Q_OBJECT
public:
Widget(QWidget *parent = 0);
QSize minimumSizeHint() const;
QSize sizeHint() const;
enum color c;
void setColor(enum color color1);
protected:
void initializeGL();
void paintGL();
void resizeGL(int width, int height);
};
enum color is just an enum declared ina another header file
enum color
{
red,
green,
blue
};

Answer 1

Your Slots
void redSlot(Widget w);
void greenSlot(Widget w);
void blueSlot(Widget w);
all take a Parameter of Type Widget. This tries to create a copy of the object when called. Your Widget is a subclass of QGLWidget which has a private copy constructor and therefore can't be called from a subclassed object.
As you want to change the color of an existing object and not a copy of it you should change the functions to take a pointer of that object:
void redSlot(Widget*);
void greenSlot(Widget*);
void blueSlot(Widget*);
void MainWindow::redSlot(Widget* w)
{
w->setColor(red);
}