title: compare two NSDate fails
body: <p>I try to compare two NSDate objects.
  But it fails all the time and I can not see what is wrong.</p>
  
  <pre><code>  -(IBAction)nextAction
  {
      NSDate *today = [NSDate date];
      if([appStateDate compare:today] == NSOrderedAscending) {
          dispatch_async(calcQueue, ^{ [self plusOneDate]; });
      }
  }
  </code></pre>
  
  <p>Without the code it works fine.</p>
  
  <p>it just crashes, and EXE_BAD_ACCESS on this line in the main method.</p>
  
  <pre><code> int retVal = UIApplicationMain(argc, argv, nil, nil);
  </code></pre>
  
  <p>And prints</p>
  
  <pre><code>'+[ compare:]: unrecognized selector sent to class 0x634d7e0`'
  </code></pre>
  
  <p>Im not good at using the debugger, so if you know any good tutorials or guides i like to know them to ;)  sorry for my english</p>