Why isn't my UISlider animating?

the setValue animated parameter doesn't actually perform an animation, but rather it enables animation.

To trigger the animation, you need to use UIView.animateWithDuration, and pass in the setValue command as the animation:

UIView.animateWithDuration(0.2, animations: {
  self.mySlider.setValue(0, animated:true)
})

Swift 5

UIView.animate(withDuration: 0.2, animations: {
  self.mySlider.setValue(0, animated:true)
})