Add a blur effect to a UIButton

This can be done by creating the blur as you did and inserting it below the titleLabel of the UIButton. It's important to disable user interaction in order to allow the touches to not be intercepted by the the visual effect view and forwarded to the button.

Swift 4.2:

let blur = UIVisualEffectView(effect: UIBlurEffect(style:
            UIBlurEffect.Style.light))
blur.frame = buttonForDisabling.bounds
blur.isUserInteractionEnabled = false //This allows touches to forward to the button.
buttonForDisabling.insertSubview(blur, at: 0)

If you are using a button with an image, bring the imageview to front:

buttonForDisabling.bringSubview(toFront: buttonForDisabling.imageView!)

or just use this extension:

import Foundation
import UIKit

extension UIButton
{
    func addBlurEffect()
    {
        let blur = UIVisualEffectView(effect: UIBlurEffect(style: .light))
        blur.frame = self.bounds
        blur.isUserInteractionEnabled = false
        self.insertSubview(blur, at: 0)
        if let imageView = self.imageView{
            self.bringSubview(toFront: imageView)
        }
    }
}