title: Error when calling allKeys on NSDictionary containg JSON objects
body: <p>I am working through Apple's sample code for displaying a Twitter feed from here <a href="http://bit.ly/x4nhG5" rel="nofollow">http://bit.ly/x4nhG5</a> </p>
  
  <p>From the example, the code is taking the JSON and putting it into an NSDictionary:</p>
  
  <pre><code>        NSDictionary *publicTimeline = [NSJSONSerialization JSONObjectWithData:responseData options:0 error:&amp;jsonParsingError]; 
  </code></pre>
  
  <p>What I was just trying to do at this point was look at all the keys that came back by doing this:</p>
  
  <pre><code>NSArray *allKeysArray = [publicTimeline allKeys];
  </code></pre>
  
  <p>I then receive an error while trying to run the program:</p>
  
  <blockquote>
    <p>Terminating app due to uncaught exception
    'NSInvalidArgumentException', reason: '-[__NSCFArray allKeys]:
    unrecognized selector sent to instance 0x6a950f0'</p>
  </blockquote>
  
  <p>Any reason why this NSDictionary that is loaded from a JSON is behaving this way?</p>
  
  <p>Thanks,
  Flea</p>