Retrieving data from NSDictionary and putting it into an NSMutableArray - ios

Question

I am trying to get a value from an NSDictionary and put it into an NSMutableArray. Here's some of my code for example.
- (IBAction)pressedButton:(id)sender {
NSInteger numberOfResults = 3;
NSString *searchString = #"EMINEM";
NSString *encodedSearchString = [searchString stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
NSString *finalSearchString = [NSString stringWithFormat:#"https://itunes.apple.com/search?term=%#&entity=song&limit=%li",encodedSearchString,(long)numberOfResults];
NSURL *searchURL = [NSURL URLWithString:finalSearchString];
dispatch_queue_t iTunesQueryQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_async(iTunesQueryQueue, ^{
NSError *error = nil;
NSData *data = [[NSData alloc] initWithContentsOfURL:searchURL options:NSDataReadingUncached error:&error];
if (data && !error) {
NSDictionary *JSON = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:nil];
NSArray *array = [JSON objectForKey:#"results"];
NSMutableArray *arrayTracks;
for (NSDictionary *bpDictionary in array) {
[arrayTracks addObject:[bpDictionary objectForKey:#"trackName"]];
// _author = [bpDictionary objectForKey:#"trackName"];
dispatch_async(dispatch_get_main_queue(), ^{
self.label.text = [arrayTracks objectAtIndex:0];
// self.label2.text = _author;
// NSLog(#"%#", [array objectAtIndex:0]);
});
}
}
});
}
As you can see from the above, it does not properly put the value into the array. If I set the _author to [bpDictionary objectForKey:#"trackName"] then it does work, but it goes through it all and sets the label as the last in the array. The above code outputs nothing (null).

Answer 1

Leverage foundation to your advantage, there's no need to iterate the array manually.
To get an array of track names you can simply use valueForKey: or valueForKeyPath:
NSArray *trackNames = [JSON valueForKeyPath:#"results.trackName"];
That being said, I urge you to perform networking tasks with networking API. You should never be using NSData to retrieve JSON. Stick to NSURLSession, it's cleaner and designed for networking tasks.
[[[NSURLSession sharedSession] dataTaskWithURL:itunesSearchURL
completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
// now you have a properly downloaded JSON
//and you even have access to the URL response headers and any errors.
}]resume];
Edit
As an aside, you never initialize your array of trackNames so calling addObject on a nil value will have no effect.