On Jul 13, 2010, at 7:53 AM, Graham Cox wrote:
> It appears that calling -setValue:forKey: on an object bypasses or ignores
> any invocation forwarding it has set up, unless I'm missing some obvious
> error.
>
> I have an object that acts as a wrapper for another object, and so that the
> wrapper can, under some circumstances, act as the thing it is wrapping, it
> implements invocation forwarding using the 'classic' approach of overriding
> -respondsToSelector:, -methodSignatureForSelector: and -forwardInvocation:
> but when I call -setValue:forKey: on the wrapper (where key is implemented by
> the thing wrapped), it throws the 'not key-value coding compliant for key'
> exception. The stack trace appears to show that this failure occurs before it
> has even attempted to follow the forwarded path. However if I simply call the
> wrapped property setter directly, the forwarding works. As this needs to work
> on 10.5, I can't use the 10.6 solution of -forwardingTargetForSelector: (not
> that I've tested it to see if it exhibits the same issue or not).
>
> Is this the expected behaviour?
Well, the documentation (KVC Programming Guide, Accessor Search Implementation
Details) says that the pattern for setValue:forKey:
• The receiver’s class is searched for an accessor method whose name
matches the pattern -set<Key>:.
So the question is "what does 'searched' mean"? Since that document talks
about method names that match certain patterns, I'm guessing that it walks the
method table (instead of calling respondsToSelector:).
I'd just override valueForKey: and setValue:forKey: in your class to handle
forwarding those to your wrapped object.
Glenn Andreas [email protected]
The most merciful thing in the world ... is the inability of the human mind to
correlate all its contents - HPL
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