iOS Flickr how to get ID

Question

In the following example I would like to access the ID value from the Flickr JSON (see below):

{
page = 1;
pages = 336567;
perpage = 20;
photo =     (
            {
        farm = 6;
        id = 10573655046;
        isfamily = 0;
        isfriend = 0;
        ispublic = 1;
        owner = "32491986@N08";
        secret = 91349d9115;
        server = 5533;
        title = DSC09356;
    },
            {
        farm = 8;
        id = 10573936633;
        isfamily = 0;
        isfriend = 0;
        ispublic = 1;
        owner = "32491986@N08";
        secret = 6abdcaa69e;
        server = 7295;
        title = DSC09118;
    }

);

So I have tried trying to use the following pattern

 NSDictionary* json = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&error];

if(json == nil){
    NSLog(@"NULL");
}else 
    NSLog(@" WORKED");

 NSArray* flickrPics = [json objectForKey:@"photos"];
 NSLog(@"Details: %@", flickrPics); //works
 NSDictionary* lastUpload = [flickrPics objectAtIndex:0];
 //fails on that line but the idea would have been to then
  NSNumber* id = lastUpload[@"photo"][@"id"];

This is the error

2013-10-30 13:43:50.534 JSON1[1508:1303] -[__NSCFDictionary objectAtIndex:]: unrecognized selector sent to instance 0x8ab3820

So why do I have this error (I have used this pattern on a different JSON object) So how do access the id ?

Answer 1

So I have solved the problem and the problem that needed to be recognised is that in the JSON the photo is a key which holds an array of dictionaries. So how to access specific items inside that array ?

//In this case valueForKey @"photo" will return as an array
NSArray *results = [flickr valueForKey:@"photo"];
//next we can iterate through the array. Each element of the Array is a dictionary
  for(NSDictionary *UserPhotoData in results){
//now we can retrieve the ID (or whatever piece of data you require 
    NSNumber *getId = [UserPhotoData valueForKey:@"id"];
    NSLog(@" id %@", getId);
}

That works.

However I am not sure

1) How a developer knows what is returned by valueForKey. Sometimes it is NSArray, sometimes it is a String or a number.

Answer 2

That is because this line:

 NSArray* flickrPics = [json objectForKey:@"photos"];

Is returning a NSDictionary, not an array