title: Qt4 How to draw inside a widget?
body: <p>Qt4, QtCreator</p>
  
  <p>I am trying to draw inside Widget:</p>
  
  <pre><code>void Widget::on_pushButton_clicked()
  {
      QPainter painter;
  
      painter.begin(ui-&gt;label);
  
      QRectF rectangle(10.0, 20.0, 80.0, 60.0);
       int startAngle = 30 * 16;
       int spanAngle = 120 * 16;
       painter.drawArc(rectangle, startAngle, spanAngle);
  
      painter.end();
  }
  </code></pre>
  
  <p>But when I press button nothing happens.</p>
  
  <p>How to do this right way?</p>