Question

I’m working on a project which would be ideally suit Cocoa bindings for the UI but I’m having an issue binding the value of an object property and can’t find a suitable solution. The object is as follows:

typedef enum tagCSQuality {
    kQualityBest            = 0,
    kQualityWorst           = 1
} CSQuality;

@interface CSProfile : NSObject {
   NSString *identifier;
   NSString *name;
   CSQuality quality;
}

In the XIB, I have an object controller whose content object is bound to a “currentSelection” property of the window controller which is an instance of the above object. I’ve then bound the name and identifier which all work as expected but I cannot see how I can bind the enums.

Ideally I would like an NSPopupButton to display “Best” and “Worst” and pick the correct enum value. I have updated the enum to have an explicit numeric value and I believe that I need a value transformer to convert the values but I’m stuck on exactly how this could be implemented.

Can anyone help me out or point me in the right direction?

Thanks,
J

Answer 1

You can use an NSValueTransformerfor this.

Since the enumeration values are integers only, they are encapsulated in an NSNumber object.

An valid transformer could look like the following.

+(Class)transformedValueClass {
    return [NSString class];
}

-(id)transformedValue:(id)value {
    CSQuality quality = [value intValue];
    if (quality == kQualityBest)
        return @"Best";
    else if (quality == kQualityWorst)
        return @"Worst";

    return nil;
}

This can be bound to the Selected Value binding of the NSPopupButton.

If you want to create a bidirectional binding (i.e. be able to select something in the NSPopupButton you have to add the following code for the reverse transformation:

+(BOOL)allowsReverseTransformation {
    return YES;
}

-(id)reverseTransformedValue:(id)value {
    if ([@"Worst" isEqualToString:value]) 
        return [NSNumber numberWithInt: kQualityWorst];
    else if ([@"Best" isEqualToString:value]) 
        return [NSNumber numberWithInt: kQualityBest];

    return nil;
}