title: Cocoa: Avoiding 'Updates Continuously' in control binds
body: <p>I have several panels that contain <code>NSTextField</code> controls bound to properties within the <em>File's Owner</em> object.  If the user edits a field and then presses <em>Tab</em>, to move to the next field, it works as expected.  However if the user doesn't press <em>Tab</em> and just presses the OK button, the new value is not set in the <em>File's Owner</em> object.</p>
  
  <p>In order to workaround this I have set <em>Updates Continuously</em> in the binding, but this must be expensive  (EDIT: or at least it's inelegant).</p>
  
  <p>Is there a way to force the bind update when the OK button is pressed rather than using <em>Updates Continuously</em>?</p>