UISwitch Value Change Listener : Swift

Suneet Agrawal
2 min readApr 13, 2022

Adding an value change event to a UISwitch is something that is required most of the time. For views like UISwitch, we can connect an IBAction with the event type as value changed and get a callback for the value changed.

This post was originally posted at https://agrawalsuneet.github.io/blogs/uiswitch-value-change-listener-swift/ and reposted on Medium on 13th April 2022.

If you are not using xib or storyboard but creating the layout programmatically or by using swiftUI, you can the editing event using a target action that takes three parameters,

  1. target of Any type which is nullable
  2. action of Selector type
  3. controlEvents of UIControl.Event

The code for the same will look like below.

//swift code in viewcontrollerself.switch.addTarget(self, action: #selector(onSwitchValueChanged(_:)), for: .valueChanged) @objc private func onSwitchValueChanged(_ switch: UISwitch) {
//do something here
}

Since the Selector takes only @objc functions which can only be defined as a member of the class or an extension of the class, we need to define it at a class level only.

@objc can only be used with members of classes, @objc protocols, and concrete extensions of classes

This way is a bit inefficient as we need to add one function for each UISwitch where we need editing event.

There is a better way where we can add this functionality to each UISwitch without making our class messy.
We can add this to the UISwitch extension itself which will be a very clean approach and will make our life super easy.

First, add a function as an extension to UISwitch class which takes a function as a parameter with 0 params and Void return type.
Since this function will be our callback function, add @escaping to the function passed as the parameter.

//MARK: - UISwitch Extension
extension UISwitch {
func setOnValueChangeListener(onValueChanged :@escaping () -> Void){

}
}

Please continue reading at https://agrawalsuneet.github.io/blogs/uiswitch-value-change-listener-swift/

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