async image loading

gistfile1.m

    // imageView is a UIImageView
    NSURL* imageNSURL = [NSURL URLWithString:value];

    dispatch_async(
        dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0),
        ^{
          NSData* imageData = [[NSData alloc] initWithContentsOfURL:imageNSURL];
          dispatch_async(
              dispatch_get_main_queue(),
              ^{
                imageView.image = [UIImage imageWithData:imageData];
                [imageData release];
              });
        });