How to run the iPhone app in Background State

During the image downloading from the url or from web services like XML/ JSON, and loading the same images in the image view will slow down the app or it may lead the app to get freezed, when the image downloaded in a synchronous way.

To avoid this,

• Asynchronous image downloading will avoid such circumstance,  here is the coding for displaying the image from the url,
• and displaying it in the UITableView Cell,

 NSString *stringURL=[NSString stringWithFormat:@"http://www.xxx.xml"];  //or it may be JSON or any php URL

 NSURL *imageURL=[NSURL URLWithString: stringURL];

    

    dispatch_queue_t concurrentQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

    //this will start the image loading in bg

    dispatch_async(concurrentQueue, ^{        

        NSData *image = [[NSData alloc] initWithContentsOfURL:imageURL];

        

        //this will set the image when loading is finished

        dispatch_async(dispatch_get_main_queue(), ^{

            cell.imageView.image = [UIImage imageWithData:image];

        });

    });

• Here, what we have done is, creating a separate queue (concurrentQueue) for the process of downloading the image from the URL,
• After the finish of downloading, we just displaying the images in the image view of the cell in the main queue.