title: How to check MPVolumeView's route button is visible
body: <p>Is there any methods which can check the MPVolumeView's route button is visible on iPad? </p>
  
  <p>Now i can access the route button through the below code, but i have no idea why i check the button's hidden, alpha are always 0 whether it's visible or not.</p>
  
  <pre><code>for (UIButton *button in volumeView.subviews) {
      if ([button isKindOfClass:[UIButton class]]) {
          // here the button is route button
      }
  }
  </code></pre>
  
  <p>Any help are appreciate, thanks.</p>