title: UINavigationBar and new iOS 5+ appearance API - how to supply two background images?
body: <p>I want to exploit the new iOS 5 appearance API to supply custom background images to all UINavigationBar instances in my app. To do this, it's as simple as this:</p>
  
  <pre><code>[[UINavigationBar appearance] setBackgroundImage:[UIImage imageNamed:@"whatever.png"] forBarMetrics:UIBarMetricsDefault];
  </code></pre>
  
  <p>However, for each instance, I want to provide a different image depending on the value of the <code>translucent</code> property, e.g.</p>
  
  <pre><code>// For UINavigationBar instances where translucent returns YES:
  [[UINavigationBar appearance] setBackgroundImage:[UIImage imageNamed:@"whatever-translucent.png"] forBarMetrics:UIBarMetricsDefault];
  
  // Otherwise:
  
  [[UINavigationBar appearance] setBackgroundImage:[UIImage imageNamed:@"whatever.png"] forBarMetrics:UIBarMetricsDefault];
  </code></pre>
  
  <p>Given that the appearance APIs seem to be configured using class methods, is something like this possible?</p>