GCD Implementation

gistfile1.m

- (AQGridViewCell *)gridView:(AQGridView *)gridView cellForItemAtIndex:(NSUInteger)index {
    switch ([self numberOfItemsInGridView:gridView] - index) {
        case 2:
            // Favorites cell
            return [TopicListViewController favoritesCell];
        case 1:
            // Add cell
            return [TopicListViewController addCell];
        default: {
            // Topic cells
            static NSString *topicCellIdentifier = @"TopicCell";

            SubscribedTopic *subscribedTopic = [self.subscribedTopics objectAtIndex:(NSUInteger) index];
            TopicGridViewCell *cell = (TopicGridViewCell *) [gridView dequeueReusableCellWithIdentifier:topicCellIdentifier];
            if (cell == nil) {
                cell = [[[TopicGridViewCell alloc] initWithFrame:TopicGridCellRect reuseIdentifier:topicCellIdentifier] autorelease];
            }

            cell.topic = [subscribedTopic BBStackAPISite];
            [self getQuestionCountForCell:cell index:index];
            return cell;
        }
    }
}

- (void)getQuestionCountForCell:(TopicGridViewCell *)cell index:(NSUInteger)index {
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0ul);
    dispatch_async(queue, ^{
        sleep(2 * index);
        CachingStackExchangeAPIClient *apiClient = [[CachingStackExchangeAPIClient alloc] initWithDatabase:self.cacheDatabase
                                                                                                      site:cell.topic];
        [apiClient getStats:^(BBStackAPICallData *callData, NSArray *results) {
            BBStackAPISiteStatistics *stats = [results objectAtIndex:0];
            cell.questionCount = stats.totalQuestions;
        } failure:nil];
        [apiClient release];
    });
}

So we dequeue the cell like normal and set properties for things we already have. For the background loaded content, I use GCD to queue up a background task. In my async block I just sleep for a bit (I scale the sleep based on the index of the cell...probably a naive implementation) and then make the API request.

Normally you need to run the UI updating code (cell.questionCount = stats.totalQuestions) back in the UI thread but I noticed that AFNetworking does that already in the success block. Super clean and seems to work really well.