How to set the BlurRadius of UIBlurEffectStyle.Light

Question

I was wondering how to set the radius/blur factor of iOS new UIBlurEffectStyle.Light? I could not find anything in the documentation. But I want it to look similar to the classic UIImage+ImageEffects.h blur effect.

required init(coder aDecoder: NSCoder) {
    super.init(coder: aDecoder)
    
    let blur = UIBlurEffect(style: UIBlurEffectStyle.Light)
    let effectView = UIVisualEffectView(effect: blur)
    effectView.frame = frame
    addSubview(effectView)
}

Answer 1

Changing alpha is not a perfect solution. It does not affect blur intensity. You can setup an animation from nil to target blur effect and manually set time offset to get desired blur intensity. Unfortunately iOS will reset the animation offset when app returns from background.

Thankfully there is a simple solution that works on iOS >= 10. You can use UIViewPropertyAnimator. I didn't notice any issues with using it. I keeps custom blur intensity when app returns from background. Here is how you can implement it:

class CustomIntensityVisualEffectView: UIVisualEffectView {

    /// Create visual effect view with given effect and its intensity
    ///
    /// - Parameters:
    ///   - effect: visual effect, eg UIBlurEffect(style: .dark)
    ///   - intensity: custom intensity from 0.0 (no effect) to 1.0 (full effect) using linear scale
    init(effect: UIVisualEffect, intensity: CGFloat) {
        super.init(effect: nil)
        animator = UIViewPropertyAnimator(duration: 1, curve: .linear) { [unowned self] in self.effect = effect }
        animator.fractionComplete = intensity
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError()
    }

    // MARK: Private
    private var animator: UIViewPropertyAnimator!

}

I also created a gist: https://gist.github.com/darrarski/29a2a4515508e385c90b3ffe6f975df7