title: How to play keyboard click sound in custom keyboard?
body: <p>I had created custom keyboard with <code>UIView</code>.
  However, I didn't hear the click sound of the keyboard.
  So I tried following code, but I can't hear anything.
  How can I play that keyboard click sound?</p>
  <pre><code>NSURL* musicFile = [NSURL fileURLWithPath:[[NSBundle mainBundle] 
                                                 pathForResource:@&quot;Tock&quot;
                                                 ofType:@&quot;aiff&quot;]];
      AVAudioPlayer *click = [[AVAudioPlayer alloc] initWithContentsOfURL:musicFile error:nil];
      [click setVolume:0.15f];
      [click play];
  </code></pre>
  <p>And also I tried this:</p>
  <pre><code>AudioServicesPlaySystemSound(0x450);
  </code></pre>
  <p>How can I achieve this?</p>