displaying JSON data with the help of dictionaries and array - nsdictionary

Question

I get the following error
[__NSCFDictionary objectAtIndex:]: unrecognized selector sent to instance 0x75a8e20
2013-04-20 08:56:14.90 MyApp[407:c07] *** Terminating app due to uncaught
exception 'NSInvalidArgumentException', reason: '-[__NSCFDictionary objectAtIndex:]:
unrecognized selector sent to instance 0x75a8e20'
This is my first hands on working with JSON. I get the above mentioned error when I try to run the first piece of code where URL is a flickr url. When I use the photos as key it print the array and app abruptly quits.
#define flickrPhotoURL [NSURL URLWithString: #"http://api.flickr.com/services/rest/?format=json&sort=random&method=flickr.photos.search&tags=rocket&tag_mode=all&api_key=12345&nojsoncallback=1"]
- (void)viewDidLoad
{
[super viewDidLoad];
//this line of code will be executed in the background to download the contents of the flickr URL
dispatch_async(flickrBgQueue, ^{
NSData* flickrData = [NSData dataWithContentsOfURL:flickrPhotoURL]; //NOTE: synchronous method...But we actually need to implement asynchronous method
[self performSelectorOnMainThread:#selector(appFetchedData:) withObject:flickrData waitUntilDone:YES]; //when data is available "appFetchedData" method will be called
});
}
- (void)appFetchedData: (NSData *)responseData
{
//parsing JSON data
NSError *error_parsing;
NSDictionary *flickr_json = [NSJSONSerialization JSONObjectWithData:responseData options:kNilOptions error:&error_parsing];
NSArray* photo_information = [flickr_json objectForKey:#"photos"];
NSLog(#"Photo Information: %#",photo_information);
NSDictionary* photo = (NSDictionary*)[photo_information objectAtIndex:0];
humanReadable.text = [NSString stringWithFormat:#"Owner is %#",[photo objectForKey:#"Owner"]];
}
However when I run the same piece of code by replacing the key "photos" with "loans" and use the following URL and code
#define flickrPhotoURL [NSURL URLWithString: #"http://api.kivaws.org/v1/loans/search.json?status=fundraising"]
- (void)appFetchedData: (NSData *)responseData
{
//parsing JSON data
NSError *error_parsing;
NSDictionary *flickr_json = [NSJSONSerialization JSONObjectWithData:responseData options:kNilOptions error:&error_parsing];
NSArray* photo_information = [flickr_json objectForKey:#"loans"];
NSLog(#"Photo Information: %#",photo_information);
NSDictionary* photo = (NSDictionary*)[photo_information objectAtIndex:0];
humanReadable.text = [NSString stringWithFormat:#"loan amount is %#",[photo objectForKey:#"loan_amount"]];
}
, the app sets the correct information on the humanredable.text property. Am I using the wrong key for the first JSON ?

Answer 1

Firstly, thanks for publishing your Flickr API key as-is! It will be super useful for me to perform identity theft some day.
Second, another big thanks for not having read the data you got back. It starts like this:
{"photos":{"page":1, "pages":1792, "perpage":100,
^^^^^^^^^^
So the object for the key photos is a dictionary, not an array, thus,
NSArray* photo_information = [flickr_json objectForKey:#"photos"];
is wrong. Did you mean this instead:
NSArray* photo_information = [[flickr_json objectForKey:#"photos"]
objectForKey:#"photo"];
? Also, below when you construct the human readable description,
[photo objectForKey:#"Owner"]
is wrong, it should be
[photo objectForKey:#"owner"]
instead.