Re: KVO question
Re: KVO question
- Subject: Re: KVO question
- From: Sean Murphy <email@hidden>
- Date: Tue, 23 May 2006 00:12:04 -0400
On May 22, 2006, at 8:29 PM, Peter Boctor wrote:
I have a class "foo" that keeps track of a "current" object.
Another class
wants to know:
1. When foo's "current" object changed
2. When the property "bar" on foo's "current" object has changed.
and uses the following code:
[foo addObserver:self
forKeyPath:@"current"
options:NSKeyValueObservingOptionNew
context:NULL];
[foo addObserver:self
forKeyPath:@"current.bar"
options:NSKeyValueObservingOptionNew
context:NULL];
When the "current" object changes, observeValueForKeyPath is called
twice,
once with a keyPath of "current" and a second time with a keyPath
of "
current.bar". How can the observeValueForKeyPath implementation
determine
what actually changed, "current" or "current.bar"?
Hey Peter,
The only suggestion that I could think of is to disable automatic key-
value observing on the bar property of the foo object. Then, in your
accessor method for the bar object, you can determine if the bar is
actually being changed without a complete replacement of the entire
foo object beneath it (for instance: is an init method setting this
value for a brand new object?). After you verify that bar is
changing and you want KVO to activate, call willChangeValueForKey and
didChangeValueForKey to inform the observer that it should deal with
an actual change of the bar property.
Disabling automatic notification isn't an all-or-nothing option,
meaning you can selectively turn it off for only the bar key.
Check out the ADC docs for more information on Manual KVO: http://
developer.apple.com/documentation/Cocoa/Conceptual/KeyValueObserving/
Concepts/AutoVsManual.html#//apple_ref/doc/uid/20001844-178876
This probably isn't the only solution, but at least something you can
work with..
Hope it helps,
-Murph
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| | >KVO question (From: "Peter Boctor" <email@hidden>) |