Re: KVO and the observeValueForKeyPath bottleneck
Re: KVO and the observeValueForKeyPath bottleneck
- Subject: Re: KVO and the observeValueForKeyPath bottleneck
- From: Chris Kane <email@hidden>
- Date: Mon, 17 Jul 2006 11:24:04 -0700
On Jul 17, 2006, at 10:49 AM, Matt Neuburg wrote:
On Mon, 17 Jul 2006 09:09:04 -0700, Chris Kane <email@hidden> said:
On Jul 17, 2006, at 7:38 AM, Matt Neuburg wrote:
On or about 7/17/06 3:38 AM, thus spake "Jakob Olesen"
<email@hidden>:
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)
object change:(NSDictionary *)change context:(void *)context
{
if ([self respondsToSelector:(SEL)context])
[self performSelector:(SEL)context withObject:change];
}
By an incredible coincidence, yesterday (before this reponse
arrived at my
desk), after considering all the responses I'd gotten, I decided
upon an
approach and implemented it in my app, and it was word for word,
letter for
letter identical with this. m.
I'm just curious ... with the trivial approach above, and the other
ones involving the context being a keypath and so on ... has anyone
considered what will happen if a superclass or subclass (of whatever
class that is) is also doing KVO (on either same or different keys)
of the same objects?
I hadn't, but I presume you wouldn't be asking the question unless the
answer were, "Something bad...?" :) I guess you're hinting that one
needs to
call super.
No, I wasn't thinking that. Though having to call super could still
be a valid conclusion.
Simply calling super would be problematic, because NSObject doesn't
implement it (well, it throws).
No, I was pondering something more subtle to do with the context. The
basic "shunting" pattern here that is somewhat popular is
fundamentally broken, I think, because people are not considering
subclassing, and I wonder if the circumlocutions to avoid the problem
are worth the trouble.
The thing I'm really wondering is: Why was KVO implemented in this
oddly
bottleneck-based way? There is terrific prior art, in the form of
ordinary
notifications and the notification center (broadcaster-type
architecture);
is there some technical reason why KVO doesn't use that?
I'm going to have to leave you hanging on these...
Chris Kane
Cocoa Framework, Apple
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