Async image downloader

Question

I have write a little class to perform the download of the images by using an NSURLConnection. The idea it's to delegate the download to this class to avoid to block the execution.

So I pass the target UIImageView (by ref) and the url to the function and start the download:

-(void)getImage:(UIImageView**)image formUrl:(NSString*)urlStr
{
    NSLog(@"Downloader.getImage.url.debug: %@",urlStr);
    NSURL *url = [NSURL URLWithString:urlStr];
    NSURLRequest *req = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestReturnCacheDataElseLoad timeoutInterval:5.0];
    [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES];
    NSURLConnection *c = [[NSURLConnection alloc] initWithRequest:req delegate:self];
    [conn addObject:c];
    int i = [conn indexOfObject:c];
    [imgs insertObject:*image atIndex:i];
    [c release];
}

When it's finished set the image and update the imageView:

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    int i = [conn indexOfObject:connection];

    NSData *rawData = [buffer objectAtIndex:i];
    UIImage *img = [UIImage imageWithData:rawData];
    UIImageView *imgView = [imgs objectAtIndex:i];
    imgView.image = img;

    [imgView setNeedsDisplay];

    [conn removeObjectAtIndex:i];
    [imgs removeObjectAtIndex:i];
    [buffer removeObjectAtIndex:i];

    if ([conn count]==0) {
        [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];
    }
}

This system works quite good, but i can't get updated the UIImageView inside the cells of a UITableViewCell, any idea ? (actually the cell it's updated when I click on it) There is a better way to implement this functionality ? (actually the need are: non-blocking, caching system)

Answer 1

Cesar

For async image loading, caching and threaded operation, I use SDImageCache class from http://github.com/rs/SDWebImage. I also wrote my own several times, but this one is brilliant and I've thrown all my old code away.

From its documentation:

Just #import the UIImageView+WebCache.h header, and call the setImageWithURL:placeholderImage: method from the tableView:cellForRowAtIndexPath: UITableViewDataSource method. Everything will be handled for you, from async downloads to caching management.

Hilton