Re: With What does Apple Swizzle the IsA-pointer in KVO?
Re: With What does Apple Swizzle the IsA-pointer in KVO?
- Subject: Re: With What does Apple Swizzle the IsA-pointer in KVO?
- From: Jean-Daniel Dupas <email@hidden>
- Date: Fri, 23 Nov 2007 17:23:34 +0100
Le 23 nov. 07 à 17:03, Philip Mötteli a écrit :
Am 23.11.2007 um 15:54 schrieb Clark Cox:
On Nov 23, 2007 5:42 AM, Philip Mötteli <email@hidden>
wrote:
Apple says, that it uses IsA-swizzling as the underlying
technology to
implement KVO.
What are/is the class(es), which replace the original class of the
observed object? Is it an NSProxy subclass? Different NSProxy
subclasses, depending on the observed object? Is it a direct
subclass
of the observed object?
Perhaps I could provide more help if you
stated why it is that you think that you need to know this.
I need to know, when an object has changed and I would prefer to
reuse as much as possible, of what KVO already offers.
Unfortunately, KVO is based on the internals of an object (which
should be assumed as being hidden in OOP). So if I want to observe
an object that either doesn't have any declared IVar, like e. g.
NSString and many others, or does not have a corresponding IVar,
because it is not a simple setter method, like -finalize or -
dealloc, I have a problem.
Ideally, I just want to implement a plug-in, that reuses the
functionality, offered by KVO, but extends it, so that the publicly
accessible part of an object can be observed instead of the hidden
internals.
I presume, I can do that, by implementing my own proxy, that
prevents KVO to do an IsA swizzling, by implementing -
automaticallyNotifiesObserversForKey:. But I would have liked to
reuse the method forwarding mechanism of
KVO._______________________________________________
KVO is not based on the internals of an object (which is assumed to
be hidden), and it does not access hiddden internals. KVO is based on
KVC and uses accessors.
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