This is one of those things that make my brain itch. I had to puzzle over
this...
On Aug 16, 2011, at 4:18 PM, Quincey Morris wrote:
> Noting that a key path like "someObject.someArrayProperty.count" is valid, I
> think you could envisage key paths of the form
> "someObject.someArrayProperty.@0" and @1, @2, @3, etc. For this to work,
> "someObject.someArrayProperty" would have to return a NSArray subclass (or a
> compatible proxy object) that implements 'valueForUndefinedKey:' and
> recognizes the "indexing" properties from their key name syntax.
The main drawbacks would be:
* It's a pain to create an NS{Mutable}Array replacement.
* You lose the benefits of Apple's finely-tuned array classes (I'm thinking of
the automatic calculating of capacity; plus it might be hard to match them for
performance).
* You have to remember to use the replacement class in your own classes.
* You can't use this on existing classes that have array properties.
Thorsten's solution helps by mashing the array index together with the name of
the array property, so you can do:
On Aug 16, 2011, at 6:16 PM, Thorsten Hohage wrote:
> producer_0.area_0.vineyards_2.idname
However, your class has to inherit from a class that has his implementation of
valueForUndefinedKey:.
I *may* have an approach that gets around these drawbacks, although it looks a
little funny.
To summarize the problem, we'd like to be able to say something like
Employee *anEmployee = [aManager valueForKey:@"department.employees.2"];
where this would give us the second element of the employee list for a given
manager's department. We can't quite do that, but my approach comes pretty
close by inserting a pseudo-key "ARR" *before* the array property:
Employee *anEmployee = [aManager valueForKey:@"department.ARR.employees.2"];
This should work on any class with an array property like "employees".
How it works: there is a category method called "ARR" on NSObject that returns
a special wrapper object that makes everything else work. I have a quick and
dirty example project that *seems* to show this working with both setting and
getting. In my next post I'll attach the relevant source file so anybody
interested can sanity-check it.
--Andy
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