Blur effect does not fill the entire View - ios

Question

I have a View controller that features a full screen UIImageView. When the controller loads, I just set a blur effect over the whole screen. The content mode for the UIImageView is set to scaleAspectFill. I set the blur effect like this:
#IBOutlet weak var previewImage: UIImageView!
override func viewDidLoad() {
super.viewDidLoad()
previewImage.image = userPhoto
let blur = UIVisualEffectView(effect: UIBlurEffect(style: .Light))
blur.frame = self.view.bounds
previewImage.addSubview(blur)
}
when I test the app on an iPhone 6 I get this result:
There's an offset on the right an I can't figure out why. The picture underneath if is properly full screened but I can get the blur effect to fit over it...
****EDITED****
I applied the blur effect to the VC's view directly and now it works just fine, but I'd like to know why it doesn't work when I add the subview to the UIImage View...

Answer 1

I see two possible problems here:
Views are not laid out on the viewDidLoad stage. In this case you can force them to layout manualy:
override func viewDidLoad() {
super.viewDidLoad()
self.view.layoutIfNeeded()
...
}
You add subview to the previewImage, not to the root view. You must check your storyboard, or fix code:
override func viewDidLoad() {
super.viewDidLoad()
previewImage.image = userPhoto
let blur = UIVisualEffectView(effect: UIBlurEffect(style: .Light))
blur.frame = self.view.bounds
self.view.insertSubview(blur, aboveSubview: previewImage)
}

Answer 2

Based on #kelin answer. You can even add the blur effect above your image in the interface builder.Just search for Visual Effect View with Blur in the objects section in the interface builder. Then add the Visual Effect View view above your image. It is also fully customizable through Attributes inspector. That way you you make sure that the blur will occupy the entire screen. It is also cleaner from architecture perspective , you do not need to configure your view through code.