Hi,
Thanks for your reply.
The problem with this solution is that when I do a setValue:object
forKeyPath:@"preset0.parameter", and @"preset0" is the current preset,
than no KVO message is sent to observers observing the @"current"
variant of the keyPath. That would only happen, if they used the
actual @"current.parameters" keyPath.
Maybe KVO doesn't support this at all, I'm just hope it will :)
Regards,
Remco Poelstra
Op 15 feb 2011, om 19:51 heeft Quincey Morris het volgende geschreven:
On Feb 15, 2011, at 05:11, Remco Poelstra wrote:
I've a "PresetsController" which holds a dictionary containing
preset settings for my application. The presets contain trees
(Mutable Dictionaries) of keys.
To save the GUI code from bothering with tracking the current
preset, I want to give my PresetController the option to replace a
keyPath like @"current.parameter.subparameter.value" to
@"preset2.parameter.subparameter.value".
I implemented it with a valueForUndefinedKey:
- (id) valueForUndefinedKey:(NSString *)key {
if ([key isEqual:@"current"])
return [presets valueForKey:currentPreset]; //presets is a
NSMutableDicitonary, currentPreset a NSString
else
return [presets valueForKey:key];
}
, returning the dictionary belonging to the current preset. This
works for setting and reading using keyPaths. It does not work for
observing a keyPath like @"current.parameter.subparameter.value".
How should I implement that?
I think you're making this too hard. If you need to observe a key
path that includes the "current" key, then just define a [derived]
"current" property for the presets controller (assuming that's the
class that has the above code). The getter would look like this:
- (NSDictionary*) current {
return [presets valueForKey:currentPreset];
}
The only thing you have to do is make sure that "current" is KVO
compliant, which means that notifications need to be sent out
whenever the underlying value changes:
[self willChangeValueForKey: @"current"];
currentPreset = ...
[self didChangeValueForKey: @"current"];
wherever you change the current preset. There are other possible
variations, depending on what's most convenient with your class:
1. Obviously you could vary this by keeping a pointer to the current
preset dictionary in an instance variable too.
2. If "currentPreset" is itself a KVO compliant property, you don't
need to generate KVO notifications manually (the second code
fragment). Instead, you'd use:
+ (NSSet*) keyPathsForValuesAffectingCurrent {
return [NSSet setWithObject: @"currentPreset"];
}
and write:
self.currentPreset = ...
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