Re: Enable Unique Selection
Re: Enable Unique Selection
- Subject: Re: Enable Unique Selection
- From: "Gerriet M. Denkmann" <email@hidden>
- Date: Sat, 04 May 2013 11:54:42 +0700
On 3 May 2013, at 17:07, Andy Lee <email@hidden> wrote:
> On May 3, 2013, at 1:29 AM, Gerriet M. Denkmann <email@hidden> 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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