title: How to implement Spotify-like iOS app sidebar feature
body: <p>I've already implemented a sidebar like that in Facebook/Path apps with <a href="https://github.com/edgecase/ECSlidingViewController" rel="noreferrer">ECSlidingViewController</a> but I've noticed that Spotify app it's a bit different and has a very slick effect. The sidebar is not already full visible but it slides and show the icons as more as you swipe with your finger. How to animate the sidebar in this way?</p>
  
  <p>Here an image for a better explanation.</p>
  
  <p><img src="https://i.stack.imgur.com/gNHsf.jpg" alt="Spotify iOS App"></p>