I have a transient calculatedBalance property in my Account entity
that is currently implemented as a read-only property returning:
[self valueForKeyPath:@"transactio...@sum.amount"]
This appears to work but I'd like observers of this property to be
notified every time a transaction is added, modified or removed.
Having read the Core Data FAQ and several e-mails to the list I'm
aware that one method is to register the parent as an observer of
every child entity.
I thought (and that may have been my first mistake) that implementing
- (void)addTransactionsObject:(Transaction *)value
and
- (void)removeTransactionsObject:(Transaction *)value
would do the trick so I added the following lines (as appropriate) to
the XCode generated implementations...
[value addObserver:self forKeyPath:@"amount" options:0
context:ACCOUNT_BALANCE_CONTEXT]; // added this to
addTransactionsObject
[value removeObserver:self forKeyPath:@"amount"]; // added this to
removeTransactionsObject
I'm logging these methods to confirm but when I add or remove
transactions (a button triggers the remove: action of the
NSArrayController) they simply aren't getting called. Am I overlooking
something obvious? I implemented and logged -
(void)addTransactions:(NSSet *)value and -
(void)removeTransactions:(NSSet *)value too just in case but nada.
Is this the right way of approaching this problem? Should each
instance of Account be observing it's own "transactions" key and then
figuring out which Transaction instance(s) it needs to start or stop
observing? Is there some other approach I've completely overlooked?
I considered the other route suggested by the Core Data FAQ which is
to observe the application's managed object context but there'll be a
few of these dependent keys floating around and I thought it could get
messy quickly.
Thanks in advance for any help!
Matthew
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