title: subclassing initWithFileURL of an UIDocument
body: <p>I'm trying to overwrite the initWithFileURL of an UIDocument as I need to call some custom methods once an UIDocument is initialised.</p>
  
  <p>I thought this may be a good idea:</p>
  
  <pre><code>-(id)initWithFileURL:(NSURL *)url {
          self = [super initWithFileURL:url];
          // do some custom stuff
          return self;
  }
  </code></pre>
  
  <p>Is there anything else I need to do if I overwrite this? I have the feeling that I need to check for NIL or something. Where do you usually look if you need to overwrite a method with something custom? I was only able (via jump to definition when right clicking UIDocument) to see this:</p>
  
  <pre><code>    #pragma mark *** Initialization ***
  
  // The designated initializer. Passing an empty URL will cause this method to throw an NSInvalidArgumentException.
  - (id)initWithFileURL:(NSURL *)url;
  </code></pre>