By default, when I observe the value of a UISlider, it only updates once, when the slider is clicked, not continuously, even thought that is the slider's setting. Is there a way to get the continuous value change of the slider?
UIKit doesn't actively support KVO. You may be getting lucky in that some notifications may make it through the usual mechanisms, but for the most part you shouldn't assume you can use KVO with any UIKit class.
You should instead get your continuous events through the UISlider's associated target's action method.