title: UISlider does not redraw automatically
body: <p>I've an UISlider on my app and I need sometimes to update not only its value but also its minimumValue. The values are changed but if I call the setValue method or assign a new value for my slider, it has the new value but the slider does not repaint itself to the position it should be for this new value. How can I repaint it? 
  This is a piece of code where I change the minimumValue.</p>
  
  <pre><code>if([array count] &lt; 50)
      [sliderTamanyo setMinimumValue:2];
  else if([array count] &lt; 200)
      [sliderTamanyo setMinimumValue:3];
  else
      [sliderTamanyo setMinimumValue:4];
  if(sliderTamanyo.value &lt; sliderTamanyo.minimumValue)
       self.sliderTamanyo.value = self.sliderTamanyo.minimumValue;     
  [self.sliderTamanyo setNeedsDisplay];                
  </code></pre>