Swift client, dispatch async . . .

swift_client_dispatch_sync.txt

// endpoint of corresponding supply item image //
let urlString : String = supplyItem.bsn_image!

dispatch_async(self.backgroundQueue, { () -> Void in
    
    /* capture the index of the cell that is requesting this image download operation */
    var err : NSError?
    /* get url for image and download raw data */
            
    if err == nil {
            
        dispatch_sync(dispatch_get_main_queue(), { () -> Void in
                  
            /* create a UIImage object from the downloaded data */
            /* get the index of one of the cells that is currently being displayed */
                    
            // compare the captured cell index to some current cell index       //
            // if the captured cell index is equal to some current cell index   //
            // then the cell that requested the image is still on the screen so //
            // we present the downloaded image else we do nothing               //
            if /* compare indices */ {
                cell.imageView.image = itemImage
                cell.setNeedsLayout()
            }
        })
    }
})