title: Determine when a NSOpenPanel will close
body: <p>I'm trying to determine when an NSOpenPanel is closing before it actually closes. I need to do this so I can overlay another window with a screenshot of the open panel on top of it to be animated.  Unfortunately, all the notifications that you seem to be able to access seem to fire AFTER the window's already been closed. This leads to a jarring stutter before you start your transition.</p>
  
  <p>I've tried:<br>
  - using NSWindow delegate methods on the open panel (apparently, none of the NSWindow delegate methods work)<br>
  - monitoring panel:userEnteredFilename:confirmed: (not called)<br>
  - showing the dialog with a callback (callback happens AFTER the panel disappears)</p>