title: Notifying cocoa bindings system when code changes a property by instead of the interface
body: <p>I'm writing a countdown timer and instead of calling <code>-[NSTextField setDoubleValue:secondsRemaining]</code> on each tick, I'd like to bind the <code>secondsRemaining</code> property to an interface element via an object controller.</p>
  
  <p>The problem with this is that <code>secondsRemaining</code> is modified by code on each tick, not by the interface, so the change is doesn't seem to be broadcast.</p>
  
  <p>I have two parts to the question:</p>
  
  <p>1) Is this a sensible way to use bindings or should I stick with <code>-[NSTextField setDoubleValue:]</code> in my App controller?</p>
  
  <p>2) If I do use bindings, how do inform the interface that the value has changed?</p>
  
  <p>Thanks!</p>