You need to call reloadData
on your collection view after you receive the data since you're doing an asynchronous download.
[manager GET:@"http://example.com/home" parameters:parameters success:^(AFHTTPRequestOperation *operation, id responseObject) {
homeImages = [responseObject valueForKeyPath:@"pic"];
[self.collectionView reloadData];
NSLog(@"JSON: %@", homeImages);
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
NSLog(@"Error: %@", error);
}];