ios - __NSCFString objectForKeyedSubscript: exception

Question

I take datas from server. My app work fine in Sinulator and test device iPhone 4s, but one man have problem on iPod 4. He get exception:

-[__NSCFString objectForKeyedSubscript:]: unrecognized selector sent to instance 0x1d263a20

I cann't use this device so I write code to know where crash was.

 if (![dictionaryRest[@"compliments"] isEqual:[NSNull null]]) {
       NSMutableArray *array = [NSMutableArray new];
       NSMutableArray *firstArray = [NSMutableArray new];
       for (NSDictionary *dic in dictionaryRest[@"compliments"]) {
            Compliment *compl = [Compliment new];
            if (![dic[@"ID_promotions"] isEqual:[NSNull null]])
                compl.ID = [dic[@"ID_promotions"] integerValue];

So in last 2 strings this exception was. What the reason of this? So I understand that I need use

if ([dict objectForKey:[@"compliments"])

instead

if (![dict[@"compliments"] isEqual:[NSNull null]])

and in all another cases.

I test now and I have in my dictionary for ID:

Answer 1

You have an NSString instance in your dictionary where you expect a dictionary.

Note that your "use this instead of that" has nothing to do with the problem.

Answer 2

-objectForKeyedSubscript: is an instance method on NSDictionary object. __NSCFString objectForKeyedSubscript: exception indicates that the method -objectForKeyedSubscript is somehow getting called on some NSString object. So basically you just have to properly check for the class of the object before you can safely assume that it is actually dictionary.

if([dic isKindOfClass:[NSDictionary class]]) 
{
    id obj = dic[@"key"];
}