Download image asynchronously

Question

I need to download an image from the web and display it in an ImageView. Presently I am using SDWebImage (It is an asynchronous image downloader wi

Answer 1

I personally use the built in Grand Central Dispatch feature in iOS to download images from the server asynchronously.

Below is a code I used to fetch photos from Flickr in one of my apps.

In your image/photo class, have a function that is something like this:

- (void)processImageDataWithBlock:(void (^)(NSData *imageData))processImage
{
NSString *url = self.imageURL;
dispatch_queue_t callerQueue = dispatch_get_current_queue();
dispatch_queue_t downloadQueue = dispatch_queue_create("Photo Downloader", NULL);
dispatch_async(downloadQueue, ^{
    NSData *imageData = *insert code that fetches photo from server*;
    dispatch_async(callerQueue, ^{
        processImage(imageData);
    });
});
dispatch_release(downloadQueue);
}

In your Photo View Controller, you can call this function like this:

- (void)viewWillAppear:(BOOL)animated
{
[spinner startAnimating];
[self.photo processImageDataWithBlock:^(NSData *imageData) {
    if (self.view.window) {
        UIImage *image = [UIImage imageWithData:imageData];
        imageView.image = image;
        imageView.frame = CGRectMake(0, 0, image.size.width, image.size.height);
        scrollView.contentSize = image.size;
        [spinner stopAnimating];
    }
}];
}