Question

I tried using the @ char as a key in a NSDictionary and my application simply crashes. I searched for “invalid” key names, could not find the @”@” anywhere. If I use something else than @”@” it all works fine.

I have a list of comanies, I get the first letter of each company and then I am creating a NSMutableDictionary entry containing the first letter as the key and a NSMutableArray as the value.

NSMutableDictionary indexDictionary = [[NSMutableDictionary alloc] init];

// here we have a loop on companyName
{
NSString *fristLetter = [[companyName substringToIndex:1] uppercaseString];
NSMutableArray *arrayOfIndexedCompanies = [indexDictionary valueForKey:firstLetter];

    if (arrayOfIndexedCompanies) {
       [arrayOfIndexedCompanies addObject:companyName]
    }
    else {
       NSMutableArray *newArray = [NSMutableArray array];
       [indexDictionary setObject:newArray forKey:firstLetter];
       [newArray addObject:companyName];
    }
}

I enabled breakpoint break on throw and it stops at the [indexDictionary valueForKey:firstLetter]… only when firstLetter is a @”@”.
I had an if saying:

if ([firstLetter isEqualToString:@"@"]) {
    firstLetter = @"A";
}

and this works fine, it places the @ starting companies in the A section correctly. If I am letting the firstLetter unchanged (leaving it as @”@”) the application will crash.

Also, this is not really my code, I am just trying to fix it, I am not quite familiar with ObjC and Foundation so please be gentle.

Answer 1

Read the documentation 🙂

Specifically, this bit :

If key does not start with “@”, invokes objectForKey:. If key does start with “@”, strips the “@” and invokes [super valueForKey:] with the rest of the key.

I guess that super valueForKey: isn’t happy being called 🙂

To fix it, just call objectForKey: instead of valueForKey: