title: NSDictionary: convert NSString keys to lowercase to search a string on them
body: <p>I'm developing an iPhone application.</p>
  
  <p>I use a NSDictionary to store city's names as key, and population as value. I want to search the keys using lowercase.</p>
  
  <p>I've using this:</p>
  
  <pre><code>NSDictionary *dict;
  
  [dict objectForKey:[[city stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]] lowercaseString]];
  </code></pre>
  
  <p>But, it doesn't work.</p>
  
  <p>I know, I can do a for, convert keys to lowercase and compare with city.</p>
  
  <p>Is there any other way to do that? Maybe, with a NSDictionary method.</p>
  
  <p><strong>UPDATE</strong><br> The NSDictionary is loaded from a property list.</p>
  
  <p>Thank you.</p>