> On 2016 Oct 14, at 23:08, Gerriet M. Denkmann <g...@mdenkmann.de> wrote:
> My app (macOS 12) observes a value in NSUserDefaults.  Starting with macOS 12 
> observeValueForKeyPath:… is called at the start of the program, although 
> nothing has changed yet.  When the value actually changes, it is called twice.

I just added some code to one of my apps, to test this.  It confirmed your 
observations, although I only tested in 10.12.

> Also: NSKeyValueObservingOptionNew or NSKeyValueObservingOptionOld just 
> return NSNull instead of old or new values.

That only happens during that first spurious call, when the observer is added.

> Any workaround for these multiple (and unnecessary) calls?

As always when dealing with undocumented behavior, reverse-engineer :))  
Regarding that initial call, assuming that NSNull is not a legitimate possible 
value, use that NSNull to identify the call as spurious and ignore it.  
Regarding the later duplicate calls, ignore if the new value is the same as the 
current value.  I have seen Cocoa emit such redundant notifications or 
observations in other situations, and have had success filtering them in this 

You can often get clues about such changes in macOS releases by carefully 
searching Apple’s Release Notes for something related, or by filing a 
well-written Bug Report – I’ve received short explanations, anonymous, but 
obviously written by an engineer on the relevant team.  If indeed this behavior 
is new in 10.12, it certainly warrants a Bug Report.


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