Re: Manual KVO and will/didChangeValueForKey
Re: Manual KVO and will/didChangeValueForKey
- Subject: Re: Manual KVO and will/didChangeValueForKey
- From: Tim Lucas <email@hidden>
- Date: Fri, 3 Jun 2005 12:48:31 +1000
On 03/06/2005, at 2:12 AM, mmalcolm crawford wrote:
On Jun 1, 2005, at 11:51 PM, Tim Lucas wrote:
On 02/06/2005, at 3:47 PM, Andrew White wrote:
I'd like to be able to mirror the will/did messages from otherclass
in this class. I'd also like to make sure that I don't update data
twice in observeValueForKeyPath:ofObject:change:context:, once on
the willChangeValueForKey and once on the didChangeValueForKey.
I think willChangeValueForKey: just gives the any NSEditor's the
chance to finish their editing (anybody confirm this?) -- it won't
send out a KVO change notification.
Umm, no. It gives the observation mechanism an opportunity to record
pre-change values.
Ok my bad. I wasn't sure, and hence the "i think".
If willChangeValueForKey: is purely for the observation mechanism then
maybe the docs should read "Invoked to inform *the key value observing
mechanism* that the receiver is about to change the value of key"
rather than "Invoked to inform *observers* that the receiver is about
to change the value of key":
http://developer.apple.com/documentation/Cocoa/Reference/Foundation/
ObjC_classic/Protocols/NSKeyValueObserving.html#//apple_ref/doc/uid/
20002299-BBCCIJAJ
There's a few other places in that doc that might also need correcting
along those lines, if that is indeed the case.
Maybe it should also be stated somewhere in that doc that it's the
willChangeValueForKey: call that allows the KVO system to record
pre-change values for those observers who've registered using
NSKeyValueObservingOptionOld.
I've submitted it to bug reporter -- rdar://4138202
- tim lucas
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