title: How to deal with `Use of undeclared identifier 'UIDevice'`
body: <p>I followed the MD file step by step. But there is still an error in the compilation. What can I do?</p>
  
  <p>In the FaceppClient.m file :</p>
  
  <pre><code>if ([[[UIDevice currentDevice] systemVersion] compare: @"5.0" options: NSNumericSearch ] != NSOrderedAscending)
      _ios50orNewer = true;
  </code></pre>
  
  <p>Xcode outputs this error :</p>
  
  <blockquote>
    <p>Use of undeclared identifier 'UIDevice'</p>
  </blockquote>
  
  <p>I added <code>#import "UIDevice.h"</code> in the file, but Xcode outputs <code>"UIDevice.h not found"</code>.</p>
  
  <p>I added the <code>UIKit</code> framework to the Project, but I still have the compilation issue.</p>
  
  <p>What can I do then?</p>