Widget does not update

I have probably (surely?) made a mistake somewhere but...impossible to find it out! Could you help please?

Code:

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class CircleParameter : public QWidget
{
  Q_OBJECT
 
public:
  CircleParameter(QWidget *parent=0);
  virtual ~CircleParameter() {};
 
public slots:
  void setRadius(int radius);
 
protected:
  void paintEvent(QPaintEvent *e);
 
private:
  int radius;
};
 
CircleParameter::CircleParameter(QWidget *parent)
  : QWidget(parent)
{
  printf("creating widget\n");
  this->radius = DEFAULT_RADIUS;
  this->resize(MAX_RADIUS*2, MAX_RADIUS*2);
  if (updatesEnabled()) printf("yes\n"); else printf("no\n");
  if (isVisible()) printf("yes\n"); else printf("no\n");
}
 
void
CircleParameter::setRadius(int radius)
{
  printf("setRadius()\n");
  if (updatesEnabled()) printf("yes\n"); else printf("no\n");
  if (isVisible()) printf("yes\n"); else printf("no\n");
  this->radius = radius>0 ? radius<=MAX_RADIUS ? radius : MAX_RADIUS : 1;
  this->update();
}
 
void
CircleParameter::paintEvent(QPaintEvent *e)
{
  printf("paintEvent()\n");
  QPainter painter(this);
  QPen pen;
  pen.setColor(Qt::red);
  painter.setPen(pen);
  painter.drawEllipse(this->size().width()/2-this->radius, this->size().height()/2-this->radius, radius*2, radius*2);
}

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Outputs:
- at creation time:

Code:

---

creating widget
    yes
    no

---

- when moving a slider connected to CircleParameter::setRadius():

Code:

---

setRadius()
    yes
    yes

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Issue: why CircleParameter:: paintEvent() never executed?

If the CircleParameter widget is inside a layout, calling resize() will not work. You have to set a fixed size for your widget.

The paint event probably doesn't get called because the widget size is (0, 0).
Try printing this->size() in setRadius. It will most likely be (0, 0);

Quote:

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Originally Posted by marcel

If the CircleParameter widget is inside a layout, calling resize() will not work. You have to set a fixed size for your widget.

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I did not know about this behaviour of widgets in a layout. It works now. Thank you very much for your help!