I currently am working on developing a set of libraries for work to handle communication with Twitter. I have most of the twitter communication with twitter sorted out and working properly. The issue I am having is this, I am working on creating native data models for the returned data so that the rest of the people I work with don’t have to know a damn thing about what the twitter API returns as JSON data. I generally create my data models like this: Create a class that represents the data returned, where each attribute maps to a ObjC property. I add an initWithDictionary/initWithArray method that I use to translate the dictionary or array into an object. Generally the initWithDictionary method just calls [self setValuesForKeysWithDictionary:] and everything gets taken care of. Its lean, its mean and its quick to code. The problem I run into is when I have fields that are arrays or other objects? How do I get my code to walk down the tree of data instantiating objects as need be.

Here is an example of my code

@class TwitterUser;

@interface TwitterUserResults : NSObject { NSMutableArray *_users; // Array of TwitterUser objects }

• (id)initWithArray:(NSArray *)array;
• (NSInteger)countOfUsers;
• (TwitterUser *)objectInUsersAtIndex:(NSInteger)index;

@end

@implementation FMTwitterUserResults

#pragma mark - #pragma mark Instance Methods

• (id)initWithArray:(NSArray *)array { if(self = [super init]) { self->_users = [[NSMutableArray alloc] init];

    for(NSDictionary *dict in array) {
        [self->_users addObject:[[TwitterUser alloc] initWithDictionary:dict]];
    }   }   return self; }
  

• (NSInteger)countOfUsers { return [self->_users count]; }

• (TwitterUser *)objectInUsersAtIndex:(NSInteger)index { TwitterUser *user = [self->_users objectAtIndex:index];

  return [user autorelease]; }

@end

@class TwitterTweet;

@interface TwitterUser : NSObject { NSNumber *_contributers_enabled; NSString *_created_at; NSString *_description; NSNumber *_favourites_count; NSNumber *_follow_request_sent; NSNumber *_followers_count; NSNumber *_following; NSNumber *_friends_count; NSNumber *_geo_enabled; NSNumber *_id; NSString *_lang; NSString *_location; NSString *_name; NSNumber *_notifications; NSString *_profile_background_color; NSString *_profile_background_image_url; NSNumber *_profile_background_tile; NSString *_profile_image_url; NSString *_profile_link_color; NSString *_profile_sidebar_border_color; NSString *_profile_sidebar_fill_color; NSString *_profile_text_color; NSNumber *_profile_use_background_image; NSNumber *_protected; NSString *_screen_name; TwitterTweet *_user_status; NSNumber *_statuses_count; NSString *_time_zone; NSString *_url; NSString *_utc_offset; NSNumber *_verified; } @property (nonatomic, copy) NSNumber *contributors_enabled; @property (nonatomic, copy) NSString *created_at; @property (nonatomic, copy) NSString *description; @property (nonatomic, copy) NSNumber *favourites_count; @property (nonatomic, copy) NSNumber *follow_request_sent; @property (nonatomic, copy) NSNumber *followers_count; @property (nonatomic, copy) NSNumber *following; @property (nonatomic, copy) NSNumber *friends_count; @property (nonatomic, copy) NSNumber *geo_enabled; @property (nonatomic, copy) NSNumber *id; @property (nonatomic, copy) NSString *lang; @property (nonatomic, copy) NSString *location; @property (nonatomic, copy) NSString *name; @property (nonatomic, copy) NSNumber *notifications; @property (nonatomic, copy) NSString *profile_background_color; @property (nonatomic, copy) NSString *profile_background_image_url; @property (nonatomic, copy) NSNumber *profile_background_tile; @property (nonatomic, copy) NSString *profile_image_url; @property (nonatomic, copy) NSString *profile_link_color; @property (nonatomic, copy) NSString *profile_sidebar_border_color; @property (nonatomic, copy) NSString *profile_sidebar_fill_color; @property (nonatomic, copy) NSString *profile_text_color; @property (nonatomic, copy) NSNumber *profile_use_background_image; @property (nonatomic, copy) NSNumber *protected; @property (nonatomic, copy) NSString *screen_name; @property (nonatomic, retain) TwitterTweet *userStatus; @property (nonatomic, copy) NSNumber *statuses_count; @property (nonatomic, copy) NSString *time_zone; @property (nonatomic, copy) NSString *url; @property (nonatomic, copy) NSString *utc_offset; @property (nonatomic, copy) NSNumber *verified;

• (id)initWithDictionary:(NSDictionary *)dictionary;

@end

@implementation TwitterUser

#pragma mark - #pragma mark Synthesized Properties @synthesize contributors_enabled = _contributors_enabled; @synthesize created_at = _created_at; @synthesize description = _description; @synthesize favourites_count = _favourites_count; @synthesize follow_request_sent = _follow_request_sent; @synthesize followers_count = _followers_count; @synthesize following = _following; @synthesize friends_count = _friends_count; @synthesize geo_enabled = _geo_enabled; @synthesize id = _id; @synthesize lang = _lang; @synthesize location = _location; @synthesize name = _name; @synthesize notifications = _notifications; @synthesize profile_background_color = _profile_background_color; @synthesize profile_background_image_url = _profile_background_image_url; @synthesize profile_background_tile = _profile_background_title; @synthesize profile_image_url = _profile_image_url; @synthesize profile_link_color = _profile_link_color; @synthesize profile_sidebar_border_color = _profile_sidebar_border_color; @synthesize profile_sidebar_fill_color = _profile_sidebar_fill_color; @synthesize profile_text_color = _profile_text_color; @synthesize profile_use_background_image = _profile_use_background_image; @synthesize protected = _protected; @synthesize screen_name = _screen_name; @synthesize userStatus = _user_status; @synthesize statuses_count = _statuses_count; @synthesize time_zone = _time_zone; @synthesize url = _url; @synthesize utc_offset = _utc_offset; @synthesize verified = _verified;

#pragma mark - #pragma mark Instance Methods

• (id)initWithDictionary:(NSDictionary *)dictionary { if(self = [super init]) { [self setValuesForKeysWithDictionary:dictionary]; } return self; }

• (void)setStatus:(NSDictionary *)dict { self.userStatus = [[TwitterTweet alloc] initWithDictionary:dict]; }

@end

So my question is how do I solve this problem of instantiating relations between objects and keep every thing KVC compliant?

I’ve read most of Apples Docs on KVC, but I don’t understand how to properly set it up so that setValuesForKeysWithDictionary: will call a method like addUsersObject: for each sub-tree of a trend object in the returned JSON object. Any advice would be helpful.

Thanks -Laveur

---

Not that I’ve thought about this deeply, but� how about writing setter accessors for those attributes that require special handling? I would expect setValue:forKey to call a written accessor for a property if you write one. There are a few ways to do that - use the suggested naming pattern and skip @synthesize, or I think you can @synthesize the getter and specify the setter in the @property declaration. – PaulCollins