Set UIImageView as background - Swift 4 - swift

Question

I want to set a background image behind everything that already exists in the view.
I tried :
override func viewDidLoad() {
super.viewDidLoad()
let backgroundImage = UIImageView(frame: UIScreen.main.bounds)
backgroundImage.image = UIImage(named: "bg-img")
backgroundImage.contentMode = UIViewContentMode.scaleAspectFill
self.view.insertSubview(backgroundImage, at: 0)
}
But it didn't work (it didn't even add the img). So I imported the ImageView component and added the image using the Xcode GUI and it did add the image but is on top of everything. I have tried several Stack Overflow answers (that's where I get the above code from), but I didn't have any luck.
My folder structure looks like this:
My image is inside the Assets.xcassets folder.
UPDATE:
I restarted Xcode and my code worked.

Answer 1

Setting the subviews' frames in viewDidLoad is not a good practice because subviews aren't yet correctly placed at that point. You should set the frames of subviews in viewDidLayoutSubviews, which is called after the self.view and it's subviews are correctly laid out.
Your ViewController:
var backgroundImage: UIImageView!
override func viewDidLoad() {
super.viewDidLoad()
self.backgroundImage = UIImageView(image: UIImage(named: "bg-img"))
self.backgroundImage.contentMode = .scaleAspectFill
self.view.insertSubview(self.backgroundImage, at: 0)
}
override func viewDidLayoutSubviews() {
super.viewDidLayoutSubviews()
self.backgroundImage.frame = self.view.bounds
}

Answer 2

All you have to do is give the full name of the jpg image:
backgroundImage.image = UIImage(named: "bg-img.jpg")
If it were placed in Assets.xcassets, or a png file, then specifying the extension would have been optional.
Sometimes all you need is to Clean your Build Folder ⇧⌘K, or just restart Xcode.