I have a UICollectionView in which I've created a class that inherits for UICollectionViewCell. The new class includes an image outlet variable. 

The code that I have written thus far displays the cells once all the images have completely downloaded, I would like to load these images asynchronously so each cell gets populated as each individual image gets downloaded from Flickr.

How do I get grand central dispatch to handle this for me?

Here's my code : 

```
import UIKit
import MapKit
import CoreData

class ImagesCollectionViewController : UIViewController, UICollectionViewDataSource, UICollectionViewDelegate{

    @IBOutlet weak var mapView: MKMapView!

    @IBOutlet weak var collectionView: UICollectionView!
    var mapLat : Double!
    var mapLong : Double!
    let flickrApi = Flickr()
    var imageURLSet = [String]()

    override func viewDidLoad() {

        // set the location and zoom of the minimap
        let clLocation = CLLocationCoordinate2D(latitude: mapLat, longitude: mapLong)
        let span = MKCoordinateSpan(latitudeDelta: 2, longitudeDelta: 2)

        mapView.setRegion(MKCoordinateRegion(center: clLocation, span: span), animated: false)
        mapView.scrollEnabled = false

        getImages()
    }

    func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return imageURLSet.count
    }

    func numberOfSectionsInCollectionView(collectionView: UICollectionView) -> Int {
        return imageURLSet.count
    }

    func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {

        let cell = collectionView.dequeueReusableCellWithReuseIdentifier("ImageCell", forIndexPath: indexPath) as! FlickrImageCellViewController

        // This is where the cells are being populated
        let url = NSURL(string: imageURLSet[indexPath.row])
        let data = NSData(contentsOfURL: url!)
        let img = UIImage(data: data!)
        cell.imageView.image = img

        return cell
    }

    //Get images from the flickr API and store in array

    func getImages(){

        let parameters : [String : AnyObject] = ["method": Flickr.Consts.GEO_METHOD, "format" : Flickr.Consts.FORMAT, "api_key": Flickr.Consts.API_KEY, "lat" : mapLat, "long" : mapLong, "nojsoncallback" : "1", "per_page" : "21", "extras" : "url_m"]

        flickrApi.performGetRequest(parameters) { (data, error) in

            for record in data as! [AnyObject]{
                if(record["url_m"] != nil){

                    self.imageURLSet.append(record["url_m"] as! String)

                }
            }
        }
    }

    override func viewDidAppear(animated: Bool) {

        self.collectionView.reloadData()
    }
}

```