Hello,

I’m new in cocoa programming and despite AAron Hillegass’s book, Apple’s documentation and cocoadev’s post I can’t solve my problem. Here it is :

I’m building a core data application. I want it to calculate some statistics thanks to an entity content. In my case the calculation consist in getting the max - the min value and dividing by the NSArray count property. My app is a NSTableView bound to a NSArrayController bound to a core data structure. There are an add and a remove buttons bound to the NSArrayController. Thanks to IB and bindings my app is already able to add, remove, edit and store datas. I know how to build an Entity. I know how to customize it (NSManagedObject inheritance) and I know how to fetch it (predicates). The problem is I want the calculation to be real time refreshed. I mean I want it to be recalculated when I add, edit or remove a row from the NSTableView as the calculation is based on the values of the rows. To do that I’ve learnt I should add and observer.

Here is what I did :

/////////////EntityRelev.h #import <Cocoa/Cocoa.h>

//I will use a custom managed object as entity so that I can control default values… @interface EntityRelev : NSManagedObject { }

@end

////////////EntityRelev.m #import “EntityRelev.h”

@implementation EntityRelev

//Adds an observer on each object so that I can trigger my calculations when one is added, editied or removed

• (void) awakeFromEverything { [self addObserver:self forKeyPath:@”kmReleve” options:(NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld) context:NULL]; }

• (void) awakeFromInsert { //some initializations //adds an observer on new objects [self awakeFromEverything]; }

• (void) awakeFromFetch { //adds an observer on already stored datas and on fetched datas [self awakeFromEverything]; }

• (void) didTurnIntoFault { //should remove the observer from the close to be removed object }

• (void) observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionnary *)change context:(void *)context { //perform my calculations NSLog(@”you should do it now”); }

@end

When editing pre stored objects -> the “event” is triggered -> ok When adding a new object and editing them -> the “event” is triggered -> ok When removing a previously created object -> the “event” is triggered -> ok When removing a pre stored object -> the “event” ISN’T triggered -> Problem :-(

According to what I read there is a thing about the managedcontext and faults but I can’t understand how to solve that. Is there something I should add to my class ? Is there something I missunderstood ? Please could someone help me ?

Kind Regards Xavier