Adding NSMutableArray to NSMutableDictionary and the arrays are null?

Question

I've got a simple object "post" that has two NSMutableArrays as properties. One is for "image" objects and the other is for "video" objects. At some point in the lifecycle of "post", I ask it for a dictionary representation of itself.

NSMutableDictionary *postDict = [post getDictionary];

-(NSMutableDictionary *)getDictionary{

    NSMutableArray *imgDictArry = [NSMutableArray arrayWithObjects:nil];
    NSMutableArray *movDictArry = [NSMutableArray arrayWithObjects:nil];

    for (int i = 0; i<self.images.count; i++) {
        NSMutableDictionary *imgDict = [[self.images objectAtIndex:i] getDictionary];
        [imgDictArry addObject:imgDict];
    }

    for (int i = 0; i<self.videos.count; i++) {
        NSMutableDictionary *movDict = [[self.videos objectAtIndex:i] getDictionary];
        [movDictArry addObject:movDict];
    }

    NSMutableDictionary *postDict = [NSMutableDictionary dictionaryWithObjectsAndKeys:
                                     [NSNumber numberWithBool:self.friendsOnly], @"IsFriendsOnly", 
                                     self.message, @"Message",
                                     self.shortText, @"ShortText",
                                     self.authorId, @"AuthorId",
                                     self.recipientId, @"RecipientId",
                                     self.language, @"Language",
                                     self.lat, @"Lat",
                                     self.lng, @"Lng",
                                     imgDictArry, @"Images",
                                     movDictArry, @"Videos",
                                     nil];

    return postDict;
}

As you can see, the "image" and "video" objects have their own methods for describing themselves as NSMutableDictionary objects.

-(NSMutableDictionary *)getDictionary{
    return [NSMutableDictionary dictionaryWithObjectsAndKeys:
            self.nativeURL, @"NativeURL",
            self.previewURL, @"PreviewURL",
            self.smallURL, @"SmallURL",
            self.thumbURL, @"ThumbURL",
            self.imageId, @"ImageId",
            self.width, @"Width",
            self.height, @"Height",
            nil];
}

I'm not getting any errors but my imgDictArry and movDictArry objects are turning out to be NULL after I've set them on the postDict object. If I log them to the console just before this moment, I can see the dictionary data. But the other classes requesting this object is getting null for those properties.

Answer 1

Perhaps one of your functions such as self.shortText (or self.lat...) is returning nil, in which case dictionaryWithObjectsAndKeys isn't what you expect it to be: it's truncated to the first function that returns nil...

Answer 2

Since you're using class-methods to create your arrays and dictionairies (which return autoreleased objects), you need to retain them to prevent them from beeing deallocated. that could be the problem.

    NSMutableArray *imgDictArry = [[NSMutableArray arrayWithObjects:nil] retain];
    NSMutableArray *movDictArry = [[NSMutableArray arrayWithObjects:nil] retain];

and

       NSMutableDictionary *postDict = [[NSMutableDictionary dictionaryWithObjectsAndKeys:
                                     [NSNumber numberWithBool:self.friendsOnly], @"IsFriendsOnly", 
                                     self.message, @"Message",
                                     self.shortText, @"ShortText",
                                     self.authorId, @"AuthorId",
                                     self.recipientId, @"RecipientId",
                                     self.language, @"Language",
                                     self.lat, @"Lat",
                                     self.lng, @"Lng",
                                     imgDictArry, @"Images",
                                     movDictArry, @"Videos",
                                     nil] retain];

Answer 3

I changed the postDict creation to this...

NSMutableDictionary *postDict = [NSMutableDictionary dictionaryWithObjectsAndKeys:
                                     [NSNumber numberWithBool:self.friendsOnly], @"IsFriendsOnly", 
                                     self.message, @"Message",
                                     self.shortText, @"ShortText",
                                     self.authorId, @"AuthorId",
                                     self.recipientId, @"RecipientId",
                                     self.language, @"Language",
                                     self.lat, @"Lat",
                                     self.lng, @"Lng",
                                     nil];

    [postDict setObject:imgDictArry forKey:@"Images"];
    [postDict setObject:movDictArry forKey:@"Videos"];

and it's fixed. But I don't know why.