Ashley,
I don't know how I could have been so dense. I had read that section
at least a dozen times, but somehow it never sank in. I was so
fixated on getting alternative methods of accessing ordered
collections that I'd skipped over the fact that by definition
'alternative' means "will be used if the primary/more desired methods
are not available." Thanks for pointing this out anew to me.
On May 5, 2009, at 9:49 AM, Ashley Clark wrote:
The documentation[1] about accessor search order shows that it will
prefer a method named -<key> over the corresponding -countOf<Key>
and -objectIn<Key>AtIndex: methods.
Specifically you should read the section about the search pattern
for valueForKey. The mutableArrayValueForKey proxy only details how
array modifications will be made while object access falls back to
the valueForKey search ordering.
If you've declared the songs array as a @property on the class then
it will use that first for its' data access.
[1]
http://developer.apple.com/documentation/Cocoa/Conceptual/KeyValueCoding/Concepts/SearchImplementation.html
On May 5, 2009, at 8:53 AM, Aaron Braunstein wrote:
I'm trying to understand how the proxy object which is returned
from mutableArrayValueForKey: works and I've hit a bit of a wall.
I get what the proxy is and why it exists. I have a test app which
allows me to do things to/with the collection it represents and it
all works fine. The problem is that when I try to implement some
of the methods mentioned in the developer docs under the "Key-Value
Coding Accessor Methods" section. There are some methods there
which if implemented in the hosting object (i.e. the original
recipient of the mutableArrayValueForKey: call) are to be called by
the proxy when the proxy is asked to do various things. The hitch
is that in my test app I can't get the -countOf<key> or -
objectIn<key>AtIndex methods to be invoked.
In reading through the docs, it seems that a number of methods
need to be implemented before any of these (dare I call them 'proxy
methods'?) are called. I implemented a whole slew of them -
including a number that shouldn't need to be - and ended up with
this set: (The test app is based on a Playlist->Songs->Song model
where "songs" is the NSMutableArray which lives in the Playlist
class in which I'm interested in getting a count of its member
songs.)
- (unsigned int)countOfSongs;
- (Song *)objectInSongsAtIndex:(unsigned int)index;
- (NSArray *)songsAtIndexes:(NSIndexSet *)indexes;
- (void)getSongs:(Song **)buffer range:(NSRange)inRange;
- (void)insertObject:(Song *)newSong inSongsAtIndex:(unsigned
int)idx;
- (void)removeObjectFromSongsAtIndex:(unsigned int)idx;
Even simple test code like this fails:
Playlist *myPlaylist = [[[Playlist alloc] init] autorelease];
id arrayProxy = [myPlaylist mutableArrayValueForKey:@"songs"];
[arrayProxy insertObject:[[[Song alloc] initWithName:@"test"
andLength:10] autorelease] atIndex:0];
unsigned int theCount = [arrayProxy count];
I've got all the properties defined, all the methods written,
etc. Yet when I call [arrayProxy count] my countOfSongs method in
the Playlist class isn't touched. The right answer is returned,
but it's apparently coming from the runtime going to the array
directly and getting the answer via NSArray's count method.
Oddly enough, when I do the insertObject call in line #3 the
insertObject:inSongsAtIndex: method IS called... so some of this
stuff works as I believe it is supposed to. Unfortunately it's the
other stuff that's driving me nuts. I've been working on this one
for a couple of days now and have tried everything I could come up
with - including some really silly, paranoid stuff - and have made
no progress.
Can anybody help me with a suggestion as to what I might be doing
wrong or what I'm missing?
Thanks!
--
Aaron Braunstein
"Good enough" shouldn't be. From there the fall into mediocrity and
indifference is a short one.
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