AsyncImageLoadingViewController_p1.m

/*!
 @method     
 @abstract   adds images to the queue and starts the operation queue to download them
 */
- (void) addImagesToQueue:(NSArray *)images
{
    NSLog(@"AsyncImageLoadingViewController::addImagesToQueue called");

    [self.imageQueue addObjectsFromArray:images];

    // suspend the operation queue
    [self.imageLoaderOpQueue setSuspended:YES];

    // add tasks to the operation queue
    for (NSString *imageUrl in self.imageQueue) {
        NSInvocationOperation *op = [[NSInvocationOperation alloc] initWithTarget:self
                                                                         selector:@selector(loadImage:)
                                                                           object:imageUrl];
        [self.imageLoaderOpQueue addOperation:op];
        [op release];
    }

    // clear items in the queue and resume the operation queue to start downloading images
    [self.imageQueue removeAllObjects];
    [self.imageLoaderOpQueue setSuspended:NO];
}

AsyncImageLoadingViewController_p2.m

/*!
 @method     
 @abstract   downloads images, this is the method that dispatches tasks in the operation queue
 */
- (void) loadImage:(id)arg
{
    NSLog(@"AsyncImageLoadingViewController::loadImage called");
    
    if ((arg == nil) || ([arg isKindOfClass:[NSString class]] == NO)) {
        return;
    }

    // create a local autorelease pool since this code runs not on main thread
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

    // fetch the image
    NSLog(@"AsyncImageLoadingViewController::loadImage - will download image: %@", arg);
    NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:arg]];
    UIImage *image = [UIImage imageWithData:data];

    // update tableview with the downloaded image on main thread
    [self performSelectorOnMainThread:@selector(updateTableView:) withObject:[image retain] waitUntilDone:NO];

    [pool release];
}

AsyncImageLoadingViewController_p3.m

/*!
 @method     
 @abstract   updates tableview for the newly downloaded image and scrolls the tableview to bottom
*/
- (void) updateTableView:(id)arg
{
    NSLog(@"AsyncImageLoadingViewController::updateTableView called");

    if ((arg == nil) || ([arg isKindOfClass:[UIImage class]] == NO)) {
        return;
    }

    // store the newly downloaded image
    [self.loadedImages addObject:arg];
    [arg release];

    // refresh tableview
    [self.imagesTableView reloadData];

    // scroll to the last cell of the tableview
    NSIndexPath *lastRow = [NSIndexPath indexPathForRow:([self.loadedImages count] - 1) inSection:0];
    [self.imagesTableView scrollToRowAtIndexPath:lastRow
                                atScrollPosition:UITableViewScrollPositionBottom
                                        animated:YES];
}