On Feb 22, 2008, at 10:24 AM, Keary Suska wrote:
on 2/22/08 2:45 AM, [EMAIL PROTECTED] purportedly said:
[container addObserver: self forKeyPath: @"characteristics.myarray"
options:
0 context: NULL];
AFAIK, you can't observe changes to the *contents* of an array using
the
above; you can only observe when the array object itself is
replaced. If,
however, you observe the arrangedObjects property of the array
controller,
you will get notified when objects are added or removed.
This is incorrect. There are a lot of misconceptions about what
observing an array property means, as well as when you should use
controller-layer versus model-layer logic.
When you observe a property -- in the general OO sense, not the
@property sense -- you get notified of all changes to that property.
That's what observing a property means.
For *attribute* property types like strings, numbers, and dates, a
change always means replacement. Attributes are typically immutable
value types.
For *relationship* property types like mutable arrays and mutable
sets, a change can mean wholesale replacement, or it can mean addition
or removal of objects. You'll be notified for *all* such changes, so
long as they are made correctly with respect to KVC and KVO (e.g. by
manipulating the proxy object returned by -mutableArrayValueForKey: or
-mutableSetValueForKey: for the property).
Note that when you observe a relationship property, you are observing
the relationship property itself, not the objects *related by* that
relationship property. If you care about changes to them, you need to
observe them separately.
In no case should you be trying to "work around" this from model-layer
code by observing a control-layer property like an array controller's
arranged objects, or by invoking controller-layer methods like an
array controller's add/remove object methods. You can observe
properties at the model level just fine, and manipulate them just
fine; if it's not working for you, it's because there's a bug in your
code. Post it and we'll help you find it.
-- Chris
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