Download image from URL in loop for collection view

Question

Im trying to create a collection view of images. I've tried these solutions, to download the images:
one
two
three
And
four

var tempObject = json["photos"]
                for var i = 0; i < tempObject.count; i++
                {
                    var tempImage = UIImage()

                    dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), {

                        tempImage =  UIImage(data: NSData(contentsOfURL: NSURL(string:"https://developer.apple.com/swift/images/swift-og.png")!)!)!
                    })

                    swiftImages.insert(tempImage, atIndex: i)
                }

                dispatch_async(dispatch_get_main_queue()) {

                    self.collectionView?.reloadData()
                }

But i can't get it to display the images. I'm new to networking with swift.

func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCellWithReuseIdentifier("Cell", forIndexPath: indexPath) as! ImageCollectionViewCell
        cell.imageView.image = swiftImages[indexPath.row]
        return cell
    }

Answer 1

you are adding UIImage() (the one created just before dispatch_async block) objects to swiftImages array. Please realize that dispatch_async block is executed sometime in future, It is not executed right after var tempImage = UIImage() line. Grab the image from inside dispatch block, also that's where you should fire the dispatch to main queue to reload collection. Change your code like this:

            var tempObject = json["photos"]
            for var i = 0; i < tempObject.count; i++
            {
                dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), {

                    var tempImage =  UIImage(data: NSData(contentsOfURL: NSURL(string:"https://developer.apple.com/swift/images/swift-og.png")!)!)!
                    swiftImages.insert(tempImage, atIndex: i)
                    dispatch_async(dispatch_get_main_queue()) {

                       self.collectionView?.reloadData()
                    }
                })
            }

btw loading images for collection view or table view cells is not just about reading the images, you might some time by using something like AlamofireImage.