Re: What to use observeValueForKeyPath: context
Re: What to use observeValueForKeyPath: context
- Subject: Re: What to use observeValueForKeyPath: context
- From: Jim Correia <email@hidden>
- Date: Fri, 29 Aug 2008 12:44:22 -0400
On Aug 29, 2008, at 10:56 AM, Dave Dribin wrote:
It seems that KVO best practice is to use the "context" in
observeValueForKeyPath:ofObject:change:context: to differentiate
between different key paths, rather than check key path strings for
equality. Since context is a void *, it also seems best practice to
just use some unique pointer values. For example, mmalc's Graphics
Bindings sample does this:
static void *PropertyObservationContext = (void *)1091;
static void *GraphicsObservationContext = (void *)1092;
static void *SelectionIndexesObservationContext = (void *)1093;
Your KVO context has to be unique.
If you use 1091, there is no way to guarantee that any of your
subclasses or superclasses aren't also using that magic number, so
this sets you up for possible failure.
Jim
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