title: How can Interface Builder interact with private IBOutlet?
body: <p>I see that IB job is to unarchive the Nib file, load the objects in the Nib and set those to IBOutlet properties. Some people even <a href="http://blog.8thlight.com/eric-smith/2009/04/16/dependency-inversion-principle-and-iphone.html" rel="nofollow">use IB as DI framework</a></p>
  
  <p>But IBOutlet can be private, I mean it can be declared in class extension or implementation section. So how can IB interact with these private IBOutlet?</p>
  
  <pre><code>@interface FPMovieBottomViewController ()
  
  @property (weak, nonatomic) IBOutlet UILabel *usernameLabel;
  
  @end
  </code></pre>