CODEWITHSUNDEEP
iphoneobjective-cmacoscocoakey-value-observing
maxedison
maxedison

Reputation: 17573

Key-Value-Observation -- Looking for a more elegant solution to respond to value changes

I've run into a frustrating feature of KVO: all notifications are funneled through a single method (observeValueForKeyPath:....), requiring a bunch of IF statements if the object is observing numerous properties.

The ideal solution would be to pass a method as an argument to the method that establishes the observing in the first place, but it seems this isn't possible. Does a solution exist to this problem? I initially considered using the keyPath argument (addObserver:forKeyPath:options:context:) to call a method via NSSelectorFromString, but then I came across the post KVO Dispatcher pattern with Method as context and the article it linked to which offers a different solution in order to pass arguments along as well (although I haven't gotten that working yet).

I know a lot of people have come up against this issue. Has a standard way of handling it emerged?

Upvotes: 1

Views: 242

Answers (1)

ipmcc
ipmcc

Reputation: 29946

OP asks:

Has a standard way of handling it emerged?

No, not really. There are a lot of different approaches out there. Here are some:

I can't say that any of the options I've seen seem prevalent enough to earn the title "standard way". I suspect most folks who feel motivated to conquer this issue just pick one and go with it, or write their own -- it's not as if adapting KVO to use block based callbacks is rocket science. The Method-based approach you link to doesn't seem like a step forward for simplicity. I get that you're trying to take the uncertainty of the string-based-key-path <-> method conversion out of the equation, but that kind of falls down because not all observable keys/keyPaths are methods. (If nothing else, you can observe arbitrary keys on NSMutableDictionaries and get notifications.)

It sure would be nice if Apple would release a new blocks-based KVO API, but I'm not holding my breath. But in the meantime, like I said, just pick one you like and use it or write your own and use that.

Upvotes: 1

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