title: iOS Detect system volume level change. private API or not? AVSystemController_SystemVolumeDidChangeNotification
body: <p>Can listening to <code>AVSystemController_SystemVolumeDidChangeNotification</code> NSNotification be considered (during the App Store review process) as using private API?</p>
  
  <p>In my application I need to display and update the current volume level. Volume indicator should be updated after pressing hardware volume buttons and after volume change in MPVolumeView slider.</p>
  
  <p>I've searched solution how to get notification or event of hardware volume button press and had found a number of solutions.</p>
  
  <p>For example, 
  <a href="https://stackoverflow.com/questions/7528443/iphone-detect-volume-keys-press">iPhone Detect Volume Keys press.</a></p>
  
  <p>and</p>
  
  <p><a href="https://stackoverflow.com/questions/3651252/how-to-get-audio-volume-level-and-volume-changed-notifications-on-ios-4">How to get audio volume level, and volume changed notifications on iOS?</a></p>
  
  <p>I like the solution with listening to NSNotificationCenter and it seems that the most simplest and clear solution is listening to <code>AVSystemController_SystemVolumeDidChangeNotification</code> (And it works fine)</p>
  
  <p>But there are one important thing that I want to know for sure. </p>
  
  <p>This notification name is not appearing in any official Apple documentation, and there are discussions about if this notification usage will be considered as "Using the private API" or not.</p>
  
  <p>As I understand, using the private API is connected with <em>calling private methods</em>. Thats why  using this notification key can not be considered as private API usage (because actually we are using notification name as NSString).</p>
  
  <p>Maybe somebody knows this for sure, or have experience with usage of the <code>AVSystemController_SystemVolumeDidChangeNotification</code> and app was submitted/rejected?</p>
  
  <p>Many thanks for any information!</p>