NSDictionary isn't responding to objectForKey and valueForKey - iphone

Question

I have the following
// this code is inside cellForRowAtIndexPath for a TableViewController
id answer = [self.answers objectAtIndex:indexPath.row];
if ([answer respondsToSelector:#selector(objectForKey)]) {
cell.textLabel.text = [answer valueForKey:#"answer_id"];
} else {
// I'm ending up here, instead of the cell.textLabel being set
[NSException raise:#"Answer is of invalid class" format:#"It should be able to respond to valueForKey, class: %#", [answer class]];
}
where self.answers is set to
// the question that gets passed here is a parsed single object
// from the `/questions` path
- (NSArray *)answersForQuestion:(NSDictionary *)question {
NSString *contents = [self loadContentsForPath:[question valueForKey:#"question_answers_url"]];
valueForKey:#"question_answers_url"]];
NSDictionary *data = [contents JSONValue];
NSArray *answers = [data valueForKey:#"answers"];
return answers;
}
- (NSString *)loadContentsForPath:(NSString *)path {
NSString *wholeURL = [#"http://api.stackoverflow.com/1.1" stringByAppendingString:path];
return [NSString stringWithContentsOfURL:[NSURL URLWithString:wholeURL] encoding:NSUTF8StringEncoding error:nil];
}
I'm doing exactly the same thing for loading questions which works just fine, but it seems
to fail on answers when I try to do [answers valueForKey:#"answer_id"].
I don't think this is a problem with the JSON parser, because it works fine for the /questions data.
When the debugger stops on the exception and when I try to right click -> Print Description on answers, I get
Printing description of answer:
<CFBasicHash 0x6ec1ec0 [0x1474b38]>{type = mutable dict, count = 13,
entries =>
1 : <CFString 0x6ec57d0 [0x1474b38]>{contents = "down_vote_count"} = <CFNumber 0x6e1dc00 [0x1474b38]>{value = +0, type = kCFNumberSInt32Type}
2 : <CFString 0x6ec4ee0 [0x1474b38]>{contents = "last_activity_date"} = <CFNumber 0x6ec5780 [0x1474b38]>{value = [phone], type = kCFNumberSInt64Type}
3 : <CFString 0x6ec44b0 [0x1474b38]>{contents = "community_owned"} = <CFBoolean 0x1474f68 [0x1474b38]>{value = false}
...
which to me seems like a regular hash. I tried both objectForKey and valueForKey and neither of them work, i.e.
exception 'NSInvalidArgumentException', reason: '-[__NSCFNumber isEqualToString:]: unrecognized selector sent to instance 0x6b2a330'
when I do just
cell.textLabel.text = [answer objectForKey:#"answer_id"];

Answer 1

The : is a part of the method name, so you need to do:
if ([answer respondsToSelector:#selector(objectForKey:)]) {
And then use objectForKey:, not valueForKey:. The first is to access objects in the dictionary, the later is for the so-called Key-Value Coding. So it's:
id answer = [self.answers objectAtIndex:indexPath.row];
if ([answer respondsToSelector:#selector(objectForKey:)]) {
cell.textLabel.text = [answer objectForKey:#"answer_id"];
} else {
[NSException raise:#"Answer is of invalid class" format:#"It should be able to respond to objectForKey:, class: %#", [answer class]];
}
Last but not least, it looks like the object you get out of the answer dictionary is a NSNumber, not an NSString. So you might want to change the setting of the text to:
cell.textLabel.text = [[answer objectForKey:#"answer_id"] description];

Answer 2

Actually, stack overflow's api sends back a number. That is to say that the value stored for the key answer_id is an NSNumber in the dictionary and not NSString and you should treat it accordingly.

Answer 3

you can use: --
NSDictionary *answer = [self.answers objectAtIndex:indexPath.row];
if ([answer respondsToSelector:#selector(objectForKey)]) {
cell.textLabel.text = [answer valueForKey:#"answer_id"];
} else {
[NSException raise:#"Answer is of invalid class" format:#"It should be able to respond to valueForKey, class: %#", [answer class]];
}
OR
id answer = [self.answers objectAtIndex:indexPath.row];
if (answer isKindOfClass:[NSDictionary class])
{
cell.textLabel.text = [answer valueForKey:#"answer_id"];
} else {
// I'm ending up here, instead of the cell.textLabel being set
[NSException raise:#"Answer is of invalid class" format:#"It should be able to respond to valueForKey, class: %#", [answer class]];
}