title: MPRemoteCommandCenter Error in swift 4
body: <p>I am trying to setup my app to use MPRemoteCommandCenter. I got this example from the document programming guide. I imported AVFoundation and even tried importing AVKIT, I am getting the error <strong>Use of unresolved identifier 'MPRemoteCommandCenter'</strong>. When I create an instance of MPRemoteCommandCenter.shared(). Any help would be appreciated.</p>
  
  <pre><code>func setupRemoteTransportControls() {
  
      // Get the shared MPRemoteCommandCenter
      let commandCenter = MPRemoteCommandCenter.shared()   Error //**Use of unresolved identifier 'MPRemoteCommandCenter'**
  
      // Add handler for Play Command
      commandCenter.playCommand.addTarget { [unowned self] event in
          if self.audioPlayer.rate == 0.0 {
              self.audioPlayer.play()
              return .success
          }
          return .commandFailed
      }
  
      // Add handler for Pause Command
      commandCenter.pauseCommand.addTarget { [unowned self] event in
          if self.audioPlayer.rate == 1.0 {
              self.audioPlayer.pause()
              return .success
          }
          return .commandFailed
      }
  }
  </code></pre>