NSUserDefaultsDidChangeNotification with NSUserDefaultsController

• Sean McBride NSUserDefaultsDidChangeNotification with NSUserDefaultsController Aug 03 2004, 07:00
  Hi,
  
  I'm trying to understand exactly when NSUserDefaultsDidChangeNotification
  is posted.  Or, more generally, when using NSUserDefaultsController, when
  and how can I act on the changed preferences?
  
  mmalc's "ControlledPreferences" example has been very useful, but I
  notice what I consider a strange behaviour:
  
  - if I change the textfield, NSUserDefaultsDidChangeNotification is
  posted once
  - the 1st time I click the colourwell (without changing colours), its
  posted 4 times
  - subsequent times, its not posted at all unless i change colours
  - same thing with the 'fonts' button
  - clicking the 'factory' button also gets me 4 postings
  
  4 is the number of keys this app has in its defaults database.
  
  In my app, the same happens.  But in response to the changed prefs, I
  need to do a lengthy operation, and so doing it 4 times is bad. :)
  
  I may turn off the 'appliesImmediately' flag, but I'd still like to
  understand when things are posted.  Apple's docs say only "This
  notification is posted the first time after a synchronize when a change
  is made to defaults in a persistent domain" which doesn't mean much to me.
  
  Thanks!
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• Sean McBride Re: NSUserDefaultsDidChangeNotification with NSUserDefaultsController Aug 26 2004, 06:13
  OK, so I'm replying to my own post here :), for the benefit of the
  archives I guess.
  
  But I have a new question based on my new findings, but I'll start a new
  thread.
  
  Sean McBride (<cwatson...>) on Tue, Aug 3, 2004 01:00 said:
  
  

  > I'm trying to understand exactly when NSUserDefaultsDidChangeNotification
  > is posted.  Or, more generally, when using NSUserDefaultsController, when
  > and how can I act on the changed preferences?
  >
  > mmalc's "ControlledPreferences" example has been very useful, but I
  > notice what I consider a strange behaviour:
  >
  > - if I change the textfield, NSUserDefaultsDidChangeNotification is
  > posted once
  > - the 1st time I click the colourwell (without changing colours), its
  > posted 4 times
  > - subsequent times, its not posted at all unless i change colours
  > - same thing with the 'fonts' button
  > - clicking the 'factory' button also gets me 4 postings
  >
  > 4 is the number of keys this app has in its defaults database.
  

  
  What I did not realise is that the NSUserDefaultsDidChangeNotification
  has changes for bazillions of defaults, not just those related to my app.
  I printed out all the defaults (using [[note object]
  dictionaryRepresentation]) and did a text diff and now understand why I
  see so many notifications: they are not from changes to my defaults at
  all, but the OS's:
  
  193 : <CFString 0x383fa0 [0x2b9a30e0]>{contents = "NSWindow Frame
  NSColorPanel"} = <CFString 0x383fd0 [0x2b9a30e0]>{contents =
  "325 263 201 309 0 0 1024 746 "}
  
  143 : <CFString 0xa2dcc530 [0x2b9a30e0]>{contents = "NSColorPanelMode"}
  = <CFString 0x3ca750 [0x2b9a30e0]>{contents = "6"}
  
  I guess its remembering where the colour panel goes, etc.
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