Detecting a change in UISwitch

Question

This sounds trivial but I\'m noticing some weirdness. I\'ve wired up a handler for the Value Changed event of a UISwitch. What I would expect is that each time the hand

Answer 1

Log the last state so you can tell if its changed state or has been triggered with the same state.

Answer 2

In iOS 11 a new UISwitch bug was introduced so I don't recommend subscribing to value changed events. Otherwise your callback will be triggered every time UISwitch's isOn attribute changes programmatically.

Instead:

1) Subscribe for touch up inside event:

let switch = UISwitch()
switch.addTarget(self, action: #selector(onSwitchValueChanged), for: .touchUpInside)

2) Implement the callback method:

func onSwitchValueChanged(_ switch: UISwitch) {

}

3) And now when you programmatically change isOn value, it won't trigger onSwitchValueChanged method.

switch.isOn = !switch.isOn // 'onSwitchValueChanged' is not triggered