ios - tableviewcontrollerに画像をキャッシュする

Question

TableViewcontroller のキャッシュに画像を保存したいと思います。以下のコードを書きましたが、cacheImage は常に nil です。

@property (nonatomic,strong)NSCache *imageCache;
@synthesize imageCache;

- (void)viewDidLoad
{
    [super viewDidLoad];
    self.imageCache = [[NSCache alloc] init];

}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];

    cell.textLabel.text = [[tableData objectAtIndex:indexPath.row] valueForKey:@"name"];
    cell.textLabel.font = [UIFont fontWithName:@"BebasNeue" size:24];
    cell.textLabel.textColor = [UIColor whiteColor];

    UIImage *cachedImage = [imageCache objectForKey:@"indexObject"];

    if (cachedImage) {
          dispatch_async(dispatch_get_main_queue(), ^{
              cell.imageView.image = cachedImage;
                });
         }
    else {


    NSString *imageURLString=[[tableData objectAtIndex:indexPath.row] valueForKey:@"picture"];

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        NSURL *url = [NSURL URLWithString:imageURLString];
        NSData *data = [[NSData alloc] initWithContentsOfURL:url];
        UIImage *tmpImage = [[UIImage alloc] initWithData:data];
        dispatch_async(dispatch_get_main_queue(), ^{
            UITableViewCell *newsCell = [self.grillMenuTable cellForRowAtIndexPath:indexPath];
            [imageCache setObject:tmpImage forKey:@"indexObject"];
            if (newsCell)
            {
                newsCell.imageView.image=tmpImage;
                [newsCell setNeedsLayout];
            }
        });


    });
    }
    return cell;
}

Joe のアドバイスとして次のコードを使用しましたが、それでも cell.imageview.image は常に nil です。

 NSString *imageURLString=[[tableData objectAtIndex:indexPath.row] valueForKey:@"picture"];
    [[DLImageLoader sharedInstance] loadImageFromUrl:imageURLString
                                           completed:^(NSError *error, UIImage *imgData) {
                                               cell.imageView.image = imgData;
                                               }];