Sounds like NSValueTransformer is in fact what you need.
It can take in your NSArray ref and spit out a single NSString that the
NSTextField binding can live with.
Defining NSValueTransformer subclass for every binding can be a pain.
So I use a block approach. This has the big advantage that you can capture
other variables if required - like calling a weak self method:
BPBlockValueTransformer * fooTransformer = [BPBlockValueTransformer
valueTransformerWithBlock:^id(NSArray *a) {
return [welf soSomethingWith:a];
}];
[self.fooView bind:NSValueBinding toObject:self withKeyPath:@“foo”
options:@{NSValueTransformerBindingOption: fooTransformer}];
// subclass
@interface BPBlockValueTransformer : NSValueTransformer
+ (instancetype)valueTransformerWithBlock:(id(^)(id value))block;
@property (nonatomic,strong) id (^transform)(id value);
@end
@implementation BPBlockValueTransformer
+ (instancetype)valueTransformerWithBlock:(id(^)(id value))block
{
BPBlockValueTransformer *transformer = [[self alloc] init];
transformer.transform = block;
return transformer;
}
+ (Class)transformedValueClass
{
return [NSObject class];
}
- (id)transformedValue:(id)value
{
return self.transform(value);
}
@end
> On 6 Mar 2017, at 13:32, Jeremy Hughes <moon.rab...@virginmedia.com> wrote:
>
>> From what I understand of your example, you’re not “binding” anything in a
>> Cocoa sense.
>
> In the case of the single value, the text field is set up via the Bindings
> pane of Interface Builder so that “Value" says “Bind to File’s Owner” with a
> model key path of self.value. (And “value" is declared as dynamic so that
> Swift will take care of KVO.) This works fine. Is this not a Cocoa binding?
>
> What I don’t understand is why this works for a single value but doesn’t work
> for an array of values, where I change the model key path to self.values.
>
>> What you is an NSArrayController. Bind your text field to the array
>> controller. Supply the array controller with content, and have it derive the
>> selected value, be it single or multiple.
>
> OK. I now have an array controller that is bound to File’s Owner with a model
> key path of self.values, and I then bind the text field to the array
> controller with a Controller Key value of “selection” (although I’m not sure
> that’s right, because the array is not actually displayed anywhere for users
> to select items).
>
> Now I get the following error:
>
> Cannot create number from object <_NSControllerObjectProxy: 0x6000000070b0>
> of class _NSControllerObjectProxy
>
> Jeremy
>
>
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