Re: KVO question
Re: KVO question
- Subject: Re: KVO question
- From: Gerd Knops <email@hidden>
- Date: Wed, 18 Nov 2015 09:36:08 -0600
One possible issues is that `self.thingy=x;` will trigger two change notifications for `thingy`: one for `self.dictionaryOfThings = temp;` (due to keyPathsForValuesAffectingThingy), and one when the setter exits. Depending one what your observer does this may have unforeseen side effects.
A possible workaround would be to replace `self.dictionaryOfThings = temp;` with `_dictionaryOfThings = temp;`.
Gerd
>
> On Nov 17, 2015, at 19:18, Graham Cox <email@hidden> wrote:
>
> I’m using KVO to observe a bunch of properties.
>
> Most of these properties are split out into simple things that set a single value, but internal to my object, some end up setting a common dictionary of attributes, which is also a property.
>
> I KVO observe both the simple properties and the common dictionary property. Mostly this is working, but when code directly sets the dictionary property, the other properties don’t trigger their observers, even though I’m implementing the +keyPathsForValuesAffecting<property>, which I believe should cause the additional triggering. Have I understood that right?
>
> Here’s the kind of code I have:
>
>
> @property (retain) id<NSObject> thingy;
> @property (retain) NSDicitonary* dictionaryOfThings;
>
> @implementation
>
> - (void) setThingy:(is<NSObject> thing
> {
> NSMutableDictionary* temp = [self.dictionaryOfThings mutableCopy];
> [temp setObject:thing forKey:kThingKey];
> self.dictionaryOfThings = temp;
> }
>
> - (id<NSObject>) thingy
> {
> return [self.dictionaryOfThings objectForKey:kThingKey];
> }
>
>
> + (NSSet*) keyPathsForValuesAffectingThingy
> {
> return [NSSet setWithObject:@“dictionaryOfThings”];
> }
>
>
> So what I want (expect?) is that is code sets -dictionaryOfThings directly, an observer of ‘thingy’ will be triggered. Is that right?
>
>
> —Graham
>
>
>
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