How to Keep Uiswitch State When Changing Viewcontrollers

How do i keep UISwitch state when changing ViewControllers?

Xcode 8.3 • Swift 3.1

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var switchButton: UISwitch!

    override func viewDidLoad() {
        super.viewDidLoad()
        switchButton.isOn =  UserDefaults.standard.bool(forKey: "switchState")
    }

    @IBAction func saveSwitchPressed(_ sender: UISwitch) {
        UserDefaults.standard.set(sender.isOn, forKey: "switchState")
    }
}

Pass UISwitch State from One View Controller to Another ViewController

Don't try to access another view controller's view hierarchy directly. You should treat another view controllers views (and a switch is a kind of view) as private.

Set an IBAction on your switch that points to the owning view controller. In that action save the sate of the switch to a property of your view controller.

You can then access the property from the other view controller.

Save UISwitch state in UserDefaults

This is not an answer to your original query, but an answer to another query in the comment. Question: How to set the default state of UISwitch as on, if application is launched for the first time?
Though ideally, it should be asked as another question, given it is incremental, the code is below:

import UIKit

class ViewController: UIViewController {

    let userDefaults = UserDefaults.standard

    var firstTimeAppLaunch: Bool {
        get {
            // Will return false when the key is not set.
            return userDefaults.bool(forKey: "firstTimeAppLaunch")
        }
        set {}
    }

    @IBOutlet weak var mySwitch: UISwitch!

    @IBAction func switchAction(_ sender: UISwitch) {
        userDefaults.set(sender.isOn, forKey: "mySwitchValue")
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        if !firstTimeAppLaunch {
            // This will only be trigger first time the application is launched.
            userDefaults.set(true, forKey: "firstTimeAppLaunch")
            userDefaults.set(true, forKey: "mySwitchValue")
        }

        // Do any additional setup after loading the view, typically from a nib.
    }

    override func viewDidAppear(_ animated: Bool) {
        mySwitch.isOn = userDefaults.bool(forKey: "mySwitchValue")
    }

}

Note that you could do this within AppDelegate's function:

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        // Could add the above code within this as well. Upto you. 
        return true
    }

How to check the state of an UISwitch from another ViewController in SWIFT 3?

NOTE: THIS IS THE VERSION FOR SWIFT 3:

First of all, I've set the initial state of the switch to off. I have added a button, which leads us to the secondViewController and also checks the state of the switch. Here is my code(for the View Controller which contains the switch):

    @IBOutlet weak var switch1: UISwitch!
        let defaults = UserDefaults.standard
        var switchON : Bool = false
@IBAction func checkState(_ sender: AnyObject) {
   
        if switch1.isOn{
            switchON = true
        defaults.set(switchON, forKey: "switchON")
        }
        if switch1.isOn == false{
            switchON = false
            defaults.set(switchON, forKey: "switchON")
        }
    
    }

And for the secondView:

let defaults = UserDefaults.standard
    
    override func viewDidLoad() {
        super.viewDidLoad()
        if defaults.value(forKey: "switchON") != nil{
            let switchON: Bool = defaults.value(forKey: "switchON")  as! Bool
            if switchON == true{
                self.view.backgroundColor = UIColor.red()
            }
            else if switchON == false{
                self.view.backgroundColor = UIColor.green()
            }
        }
    }
    

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