On 2015 Jan 26, at 07:00, Richard Charles <rcharles...@gmail.com> wrote:
> Where do you post the notification from for a managed object property change?
Just to clarify: Your question refers to how I do it in my real apps, using
NSNotificationCenter, not how I did it in the YouTube video, which was
demonstating KVO.
Commonly, I use a custom setter, like this:
- (void)setRating:(NSNumber*)newValue {
[self postWillSetNewValue:newValue
forKey:constKeyRating] ;
[self willChangeValueForKey:constKeyRating] ;
[self setPrimitiveRating:newValue] ;
[self didChangeValueForKey:constKeyRating] ;
}
wherein the -postWillSetNewValue:forKey: posts notifications.
> It doesn’t work in a managed object's custom public property accessor because
> the public property accessor is not called during undo redo.
Ah, I’d forgotten about that. Indeed, the undo and redo tasks registered by
Core Data do not try and put things back in order using public accessors the
way I would (screw it up). Instead, Core Data registers these annoyingly
opaque undo and redo tasks that, I presume, just change the whole object graph
to a previous (consistent) state in one fell swoop. I think that’s why Core
Data does undo and redo so reliably. But real apps often need to observe all
object changes, and so the resulting un-observability transfers the complexity
elsewhere. [1]
The way I’ve worked around that is to, as Mike Abdullah said, register for
NSObjectsChangedInManagingContextNotification. I do it in a kind of “entity
manager” class that also does some fetching, etc. But read the
NSObjectsChangedInManagingContextNotification documentation and understand the
edge cases in which this notification does not get sent. Other patches may be
necessary.
So, going back to my YouTube video, I think you should take another look at
using KVO. The fact that it "just works” with undo and redo is nice, and with
tricks like Kyle Sluder’s crafty -startObserving… and -stopObserving… methods,
the bookkeeping may be tractable.
1. Google: “there are no solutions only tradeoffs”
_______________________________________________
Cocoa-dev mailing list (Cocoa-dev@lists.apple.com)
Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com
Help/Unsubscribe/Update your Subscription:
https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com
This email sent to arch...@mail-archive.com
