valueforkey when object property is readonly and Calculated(derived)

Question

I am having trouble calling valueforkey method on a property that is calculated. For example:

@interface Value : NSObject
@property(nonatomic,getter = toString,readonly)NSString *stringVal;

-(NSString*) toString;
@end

When I call [instanceOfValueClass valueForKey:@"stringVal"] , It says it is not key-value compliant. Exact Message is :

[ valueForUndefinedKey:]: this class is not key value coding-compliant for the key stringVal.

Does key value coding works on derived properties?

Thanks

Answer 1

You have set the getter method to toString, so

 [instanceOfValueClass valueForKey:@"toString"]

should work. Note that you don't have to "rename" the getter method, you could just override the default getter:

@property(nonatomic,readonly) NSString *stringVal;

- (NSString *)stringVal
{
    NSString *s = ...; // compute property value
    return s;
}

Then both instance.stringVal and [instance valueForKey:@"stringVal"] would work, with the "same key".