macOS Confused about KVO and arrays

[Hookflash]

This whole KVO/KVC thing is throwing me for a loop, particularly when it comes to arrays. My understanding, based on chapter 9 of Hillegass's book, is that, if I want observers of an array to be notified of changes to the array (e.g., insertion and removal of elements), these changes need to happen via a proxy object obtained with "mutableArrayValueForKey." For example, when I add an element like this...

id proxy= [objWithArray mutableArrayValueForKey:@"array"];
[proxy insertObject:someObject atIndex:0];

...then anything observing "array" will be notified. That works as expected. However, Hillegass also says (as far as I can tell) that "proxy" tries to invoke "insertObject:inArrayAtIndex:" on "objWithArray" behind the scenes. This doesn't seem to be happening in my tests. Here's my code:

#import <Foundation/Foundation.h>

@interface Test : NSObject
{
	NSMutableArray *things;
}
@end

@implementation Test

- (id)init
{
	self = [super init];
	things = [[NSMutableArray alloc] init];
	return self;
}

- (void)dealloc
{
	[things release];
	[super dealloc];
}


// This should be called when I mutate 'things' via proxy, right?
- (void)insertObject:(id)obj inThingsAtIndex:(NSUInteger)i
{
	NSLog(@"insertObject:inThingsAtIndex");
	[things insertObject:obj atIndex:i];
}

@end



int main (int argc, const char * argv[]) {
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
    Test *test = [[Test alloc] init];
	
    // Get proxy to "things" in "test"
    id proxy = [test mutableArrayValueForKey:@"things"];

    // Why doesn't this result in a call to [test insertObject:inThingsAtIndex]?
    [proxy insertObject:@"Hello World!" atIndex:0];
	
    [test release];
    [pool drain];
    return 0;
}

test is an instance of Test which has a mutable array called things. Note that Test implements insertObject:inThingsAtIndex:. However, when I call insertObject:atIndex: on proxy (which was obtained through [test mutableArrayValueForKey"things"]), this does not result in a call to test insertObject:inThingsAtIndex:. Am I missing something?

 

[JoshDC]

From my reading of the documentation, sounds like the mutable proxy doesn't call those methods:

http://developer.apple.com/mac/libr...Conventions.html#//apple_ref/doc/uid/20002174

 

[Hookflash]

Ok, it seems that removeObjectInThingsAtIndex: has to be implemented as well in order for the proxy to call insertObject:inThingsAtIndex:. Confusion temporarily allayed