Parsing JSON information in Objective C (multiple levels)

Question

I'm able to parse a part of my JSON file but if I want to go deeper in the structure, I'm lost. Here's my JSON :

{
"album":[
                {
                "album_titre":"Publicité",
                "album_photo":"blabla.jpg",
                "album_videos":[
                                {
                                "titre_video":"Chauffage Compris",
                                "duree_video":"01'25''",
                                "photo_video":"chauffage.jpg",
                                "lien_video":"www.bkjas.jhas.kajs"
                                },
                                {
                                "titre_video":"NIFFF 2012",
                                "duree_video":"01'43''",
                                "photo_video":"nifff.jpg",
                                "lien_video":"www.bkjas.jhas.kajs"
                                }
                                ]
                },
                {
                "album_titre":"Events",
                "album_photo":"bloublou.jpg",
                "album_videos":[
                                {
                                "titre_video":"Auvernier Jazz",
                                "duree_video":"01'15''",
                                "photo_video":"auvernier.jpg",
                                "lien_video":"www.bkjas.jhas.kajs"
                                },
                                {
                                "titre_video":"NIFFF 2011",
                                "duree_video":"01'03''",
                                "photo_video":"nifff2011.jpg",
                                "lien_video":"www.bkjas.jhas.kajs"
                                }
                                ]
                },
                {
                "album_titre":"Culture",
                "album_photo":"bilibl.jpg"
                },
                {
                "album_titre":"Postproduction",
                "album_photo":"bizoubzou"
                }
          ]
}

And here's my objective-c code :

- (void)fetchedData:(NSData *)responseData {

NSError* error;
NSDictionary *document = [NSJSONSerialization JSONObjectWithData:responseData options:kNilOptions error:&error];

if (document==nil)
{
    NSLog( @"oops\n%@", error);
}

NSArray *album = document[@"album"];


for( NSDictionary *albumDictionary in album )
{
    [album_titre addObject:albumDictionary[@"album_titre"]];
    [album_photo addObject:albumDictionary[@"album_photo"]];

    for( NSDictionary *album_videosDictionary in albumDictionary[@"album_videos"])
    {
        [titre_video addObject:album_videosDictionary[@"titre_video"]];
        [duree_video addObject:album_videosDictionary[@"duree_video"]];
        [photo_video addObject:album_videosDictionary[@"photo_video"]];
        [lien_video addObject:album_videosDictionary[@"lien_video"]];
    }

}

[self.tableView reloadData];

}

What I can't achieve is to create an array with for example contains all "titre_video" corresponding to "album_titre":"publicité". So it should contain "Chauffage Compris" and "Nifff 2012".

I know it's a kind of easy question but I've search for a while and still not able to do it.

Thank's a lot.

Nicolas

Go to json.org and spend the 5-10 minutes it takes to learn JSON syntax. (It's very simple.) Then, as I like to say, "peel the onion", one layer at a time. Avoid, for now, "clever" constructs where you dive several layers deep in one statement. Instead, assign each "layer" to a different temp variable, to make it easier to debug. (And become familiar with the changes that occur to JSON when it's converted to NS objects and NSLoggeed -- in particular an NSArray uses the () characters instead of [].) — Hot Licks
– Hot Licks, Commented Jul 29, 2013 at 14:42

Puneet Sharma · Accepted Answer · 2013-07-29 13:37:35Z

4

The key is to understand JSON structure:

{ } - - this means the underlying object is a dictionary.

[ ]  -- this means the underlyingobject is an array

 - (void)fetchedData:(NSData *)responseData {

    NSError* error;
    NSDictionary *document = [NSJSONSerialization JSONObjectWithData:responseData options:kNilOptions error:&error];

    // all titre:video for album_titre:publicite
    NSArray *albumArray = [document objectForKey:@"album"];
    NSDictionary *dict = [albumArray objectAtindex:0];
    NSArray *videos = [dict objectForKey:@"album_videos"];

   // to fetch Videos inside album_videos
   // here you will get al the videos inside key titre_video
   NSMutableArray *titreVideoArray = [[NSMutableArray alloc]init];
   for(int i=0; i< videos.count; i++){
      NSDictionary *dict = [videos objectAtindex:i];
      NSArray *titreVideos = [dict objectForKey:@"titre_video"];
      [titreVideoArray addObject: titreVideos];
    }
   }

It seems you want to fetch all the videos relating to different "album_titre". I would suggest you to use NSPredicate .

NSArray *videos = [self videosArrayForTitle:@"Publicité" albumArray:albumArray];

Here we pass title and the albumArray from above to fetch us the videos array.

- (NSArray *)videosArrayForTitle:(NSString *)title albumArray:(NSArray *)albumArray{
NSPredicate *resultPredicate=[NSPredicate predicateWithFormat:@"SUBQUERY(album_titre, $content, $content      CONTAINS %@).@count > 0", title];
NSArray *searchResults=[albumArray filteredArrayUsingPredicate:resultPredicate];
NSArray *videos = [searchResults objectForKey:@"album_videos"];
return videos;
}

edited Jul 29, 2013 at 13:37

answered Jul 29, 2013 at 12:53

Puneet Sharma

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7 Comments

Puneet Sharma Over a year ago

Please explain why downvote. It will help me to improve the answer or remove it.

Nicolas Wilhem Over a year ago

Thanks, it seams to be near of what I need. But how can I have now an array of only "titre_video"?

Nicolas Wilhem Over a year ago

Thank you Puneet but I don't know anything about NSPredicate. Isn't it possible to stay in a simple way like I tried to do? I'll stay with only 4 albums so if its 4 blocks of code it won't be too much I think.

Puneet Sharma Over a year ago

ok. Then simply traverse array. For second element, fetch: NSDictionary *dict = [albumArray objectAtindex:1]; NSArray *videos = [dict objectForKey:@"album_videos"]; and likewise for other elements as well.

Nicolas Wilhem Over a year ago

Yeah for that it's ok I got it but now in my array "videos", I have : "titre_video", "duree_video", "photo_video", "lien_video". Can I make an array with only "titre_video"?

|

Sundeep Saluja · Accepted Answer · 2013-07-29 13:15:38Z

0

{ } denotes NSDictionary [ ] denotes NSArray

Copy your json into a text edit file and go in deep. You can use NSLog() to print the data, when you go deep.

Hope it will help you.

answered Jul 29, 2013 at 13:15

Sundeep Saluja

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