On 3 May 2013, at 17:07, Andy Lee <ag...@mac.com> wrote:
> On May 3, 2013, at 1:29 AM, Gerriet M. Denkmann <gerr...@mdenkmann.de> wrote:
>> I have a button which only makes sense when exactly one thing is selected.
>> Currently it's Enabled property is bound to Array
>> Controller.selectedObjects.@count.
>> I.e. the button is enabled if one or more things are selected.
>>
>> But I want it to be disabled when nothing is selected AND also if more than
>> one thing is selected.
>> Is there a way to do this without code?
>>
>> If not - what to do ? Create a value transformer? Or what else?
>
> I vaguely remember doing this by adding a readonly property to the array
> controller -- something like "exactlyOneIsSelected" -- with a corresponding
> getter method. Then you can bind to ArrayController.exactlyOneIsSelected.
>
> Then the question would be how to trigger KVO on that property. I don't
> remember what I did. My first thought would be to implement +(NSSet
> *)keyPathsForValuesAffectingExactlyOneIsSelected, but I'm not sure what to
> return. Maybe @"selectionIndexes"? Would @"selectedObjects.@count" work? I
> don't know if you can use aggregation in keyPaths...Affecting... methods.
>
> It might be useful to implement these methods on a category of
> NSArrayController if you need this logic in multiple places.
>
> As usual I have a nagging feeling there's a better way, but this at least
> should work.
An interesting idea.
I created a ValueTransformer like:
@implementation UniqueTransformer
+ (Class)transformedValueClass { return [ NSNumber class ]; }
- (id)transformedValue:(id)value
{
BOOL unique = [ value respondsToSelector: @selector(integerValue) ] &&
[ value integerValue ] == 1;
return @(unique);
}
@end
Seems to me rather less code. Maybe still not the best way to do it, but the
best I could think of.
Kind regards,
Gerriet.
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