title: UISlider - draw line / image to the track (bar)
body: <p>I have <code>UISlider</code> with min and max track colors. I want to draw vertical line (or image) in the middle of the slider track. This line must be there the whole time, only color on top of it will be different (min / max track color).</p>
  
  <p>If I put UIImage on the Slider background, tracks covers it. If I set clear color for tracks, I can see line, but no colors from tracks (obviously). Is there any simple way, how to do this, or I have to override drawRect method for Slider ?</p>
  
  <p>Something like on the slider in image</p>
  
  <p><img src="https://i.stack.imgur.com/JvIVL.jpg" alt="enter image description here"></p>