UIKIt has a UIVisualEffectView to add the beautiful blur effects
- from the object library  drag a UIVisualEffectView and drop it on the view that needs make it blur for your case (background)
 
declare these properties
@IBOutlet var popupView: UIView!
@IBOutlet weak var visualEffectView: UIVisualEffectView!
var blurEffect:UIVisualEffect!
in viewDidLoad put this code
    blurEffect = visualEffectView.effect
    visualEffectView.effect = nil
show a view/popup (a dialog) with blur
func presentPopUp() {
    self.view.addSubview(popupView)
    UIView.animate(withDuration: 0.4) {
        self.visualEffectView.effect = self.blurEffect
       //make tarnsform from  popupView make it show more beauty
    }
}
hide a view/popup (a dialog) and blur
func dismissPopUp () {
    UIView.animate(withDuration: 0.3, animations: {
        self.visualEffectView.effect = nil
        //make tarnsform from  popupView make it hide more beauty
    }) { (success:Bool) in
        //  dismissPopUp remove it from super View
    }
}