Question

I have a simple NSDictionary that I am trying to populate with data from an external site via JSON that is returned. The JSON that is returned is fine but I am haveing trouble getting actual data for a specific key.

Here is the JSON data printed to the console.

This is my JSON data:

(
        {
        CategoryID = 12345;
        CategoryName = "Baked Goods";
    },
        {
        CategoryID = 12346;
        CategoryName = Beverages;
    },
        {
        CategoryID = 12347;
        CategoryName = "Dried Goods";
    },
        {
        CategoryID = 12348;
        CategoryName = "Frozen Fruit & Vegetables";
    },
        {
        CategoryID = 12349;
        CategoryName = Fruit;
    },
        {
        CategoryID = 12340;
        CategoryName = "Purees & Soups";
    },
        {
        CategoryID = 12341;
        CategoryName = Salad;
    },
        {
        CategoryID = 12342;
        CategoryName = "Snack Items";
    },
        {
        CategoryID = 12343;
        CategoryName = Vegetables;
    }
)

The error I am getting is:

Terminating app due to uncaught exception
‘NSInvalidArgumentException’, reason: ‘-[__NSCFArray
enumerateKeysAndObjectsUsingBlock:]: unrecognized selector sent to
instance 0x6884000’

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {

    NSError *error = nil;
    // Get the JSON data from the website
    NSDictionary *categories = [NSJSONSerialization JSONObjectWithData:data  options:kNilOptions error:&error];

    if (categories.count > 0){
        NSLog(@"This is my JSON data %@", categories);

        [categories enumerateKeysAndObjectsUsingBlock: ^(__strong id key, __strong id obj, BOOL *stop) {
        NSLog(@"Key = %@, Object For Key = %@", key, obj); }];
}

I’m not sure why this is happening but I’m sure it’s something simple like I am using the incorrect object or something.

Help is appreciated.

Answer 1

+JSONObjectWithData:options:error: is returning an NSArray not an NSDictionary. '-[__NSCFArray enumerateKeysAndObjectsUsingBlock:] is the key part of the error message. It tells you that you are calling -enumerateKeysAndObjectsUsingBlock: on an array.

---

For this case, you could use -enumerateObjectsUsingBlock: instead.

If you are not sure wether a NSArray or an NSDictionary will be returned, you can use -isKindOf:

id result = [NSJSONSerialization …];
if ([result isKindOf:[NSArray class]]) {
    NSArray *categories = result;
    // Process the array
} else if ([result isKindOf:[NSDictionary class]]) {
    NSDictionary *categories = result;
    // Process the dictionary
}

---

From enumerateObjectsUsingBlock:

Executes a given block using each object in the array, starting with the first object and continuing through the array to the last object.

• (void)enumerateObjectsUsingBlock:(void (^)(id obj, NSUInteger idx, BOOL *stop))block

So it should be called as such

[categories enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
    NSLog(@"index = %d, Object For Key = %@", idx, obj);
}];

A quick read of the documentation really can save you lots of frustration.