title: Binding label's value to the count property of an NSArray
body: <p>I want to show in a label the current number of elements in an NSArray called pages. Following other guides  I did the following:</p>
  
  <ol>
  <li>Created an NSArrayController in IB (called pagesController) and bounded it to the NSArray pages</li>
  <li>Bounded the value property of the label to the NSArrayController with Controller Key = arrangedObjects and Model Key Path = @count</li>
  </ol>
  
  <p>The problem is that when the program is running the label always shows "0". To check if the things are working correctly I tried to log a message when the user clicks on another button (the button basically inserts a new element in the pages array): <code>NSLog(@"count = %d", [self.pagesController valueForKeyPath:@"arrangedObjects.@count"]);</code> in this case the output is correct, i.e. the current number of elements in the array printed is correct.
  Where am I mistaking? </p>