Using setValuesForKeysWithDictionary with child objects and JSON

Question

I have a json string

{"name":"test","bar":{"name":"testBar"}}

In objective c I have an object

@interface Foo : NSObject {
}
@property (nonatomic, retain) NSString * name;
@property (nonatomic, retain) Bar * bar;
@end

And I just synthesize those properties. And I have a child object with synthesized properties.

@interface Bar : NSObject {
}
@property (nonatomic, retain) NSString * name;
@end

Then here is the code where I'm trying to get into the Foo object where response is the json string above:

    SBJsonParser *json = [[SBJsonParser new] autorelease];
    parsedResponse = [json objectWithString:response error:&error];
    Foo * obj = [[Foo new] autorelease];
    [obj setValuesForKeysWithDictionary:parsedResponse];
    NSLog(@"bar name %@", obj.bar.name);

This throws an exception on the NSLog statement of:

-[__NSCFDictionary name]: unrecognized selector sent to instance 0x692ed70'

But if I change the code to it works:

NSLog(@"bar name %@", [obj.bar valueForKey:@"name"]);

I'm confused at why I can't do the first example, or am I doing something wrong?

Answer 1

-setValuesForKeysWithDictionary: isn't smart enough to recognize that the value of the key "bar" should be an instance of Bar. It's assigning an NSDictionary to that property. Thus, when you ask for the property "name," the dictionary can't field that request. However, an NSDictionary does know how to handle -valueForKey:, so it happens to work in that case.

So you need to use something smarter than -setValuesForKeysWithDictionary: to populate your objects.