Re: NSKeyValueChangeNewKey returning NSNull
Re: NSKeyValueChangeNewKey returning NSNull
- Subject: Re: NSKeyValueChangeNewKey returning NSNull
- From: Kai Brüning <email@hidden>
- Date: Sat, 22 Dec 2007 18:57:37 +0100
Mike:
I am aware of this, but have no idea why nil should be returned in my case.
Best,
Kai
>NSNull is used by KVO to represent a nil value.
>
>Mike.
>
>On 21 Dec 2007, at 18:50, Kai Brüning wrote:
>
>>Hi,
>>
>>I have a case in which a KVO change dictionary always contains NSNull under NSKeyValueChangeNewKey and no idea why.
>>
>>Observation is established like this:
>>
>> [objectToObserve addObserver:self forKeyPath:@"visiblePage"
>> options:NSKeyValueObservingOptionNew
>> context:whatever];
>>
>>objectToObserve has this pair of accessors:
>>
>>- (NSNumber*) visiblePage {
>> return [NSNumber numberWithInt:_visiblePage];
>>}
>>
>>- (void) setVisiblePage:(NSNumber*)value {
>> _visiblePage = [value intValue];
>>}
>>
>>which are declared in the interface, too:
>>
>>- (NSNumber*) visiblePage;
>>- (void) setVisiblePage:(NSNumber*)value;
>>
>>_visiblePage is an iVar of type int.
>>
>>Any idea why the change dictionary would contain NSNull for NSKeyValueChangeNewKey in this case?
>>Note: - (NSNumber*) visiblePage is not called during the whole change process, but observeValueForKeyPath:ofObject:change:context: is called on the observing object, just with the defective change dictionary.
>>
>>In a very similar case (identical observed class, slightly different observer) everything works well.
>>
>>The workaround is obvious (using valueForKey: instead of depending on the change dictionary) and works, but I'd would prefer to understand this issue.
>>
>>This is all with Xcode 3 under 10.5.1 with GC off.
>>
>>Best,
>>Kai
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