Qt - update PaintGL - c++

Question

I have done some research trough the different threads about PaintGL on SO, but I couldn't manage to find what I need to make it work / understand completely.
I am trying to draw a cube. EVerytime my pushbutton gets clicked the cube should rotate. (only when it gets clicked, no timers etc)
To determine the angle I use the variable xAngle. I am able to modify it trough the function setAngleCube(), but my cube doesn't seem to move. (I see the var 'i' being changed every time.)
why? How could I make it work?
To me it looks like the cube just keeps its value from the constructor and doesn't modiy them any more.
solution:
add this line in the slot of the pushbutton
ui->widget->setCubeAngle(ui->widget->getCubeAngle()+5);
credit to #Alexander Chernin
my code:
MyGLWidget::MyGLWidget(QWidget *parent)
: QGLWidget(QGLFormat(QGL::SampleBuffers), parent)
{
xRot = 0;
yRot = 0;
zRot = 0;
xAngle=15;
qDebug("constructor\n") ;
}
void MyGLWidget::setCubeAngle(int angle)
{
xAngle = angle;
qDebug("angle set\n");
}
int MyGLWidget::getCubeAngle()
{
return xAngle;
}
Widget::Widget(QWidget *parent) :
QWidget(parent),
ui(new Ui::Widget)
{
Glptr = new MyGLWidget();
}
void Widget::on_pushButton_clicked()
{
static int i;
i+=5;
Glptr->setCubeAngle(i);
update();
qDebug()<<i<<endl;
ui->widget->setCubeAngle(ui->widget->getCubeAngle()+5); //SOLUTION
}
void MyGLWidget::paintGL()
{
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
qDebug("painting cube\n");
qDebug()<
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glRotatef(getCubeAngle(),0.0,1.0,0.0); //rotate 30 degress around y-axis
glRotatef(5.0,1,0.0,0.0); //rotate 15 degress around x-axis
glBegin(GL_QUADS);
//back
glColor3f(1,0,0);
glVertex3f(-0.5, 0.2,-0.5 );
glVertex3f(-0.7, 0.2,-0.5);
glVertex3f(-0.7, -0.2,-0.5 );
glVertex3f(-0.5, -0.2,-0.5);
//some similar code to draw other sides of the cube
}

Answer 1

try to call updateGL() in MyGLWidget::setCubeAngle:
void MyGLWidget::setCubeAngle(int angle)
{
xAngle = angle;
qDebug("angle set\n");
updateGL();
}