Setting and Saving UISwitch Value Error

Question

My problem is that the UISwitch I have in my settings page keeps reverting to an off state once you leave the settings page meaning there is no way of using the switch properly. I did some searching around and found this question and answer: How do i keep UISwitch state when changing ViewControllers?

I read this page and added the answer to my code:

@IBOutlet weak var NumSwitch: UISwitch!

override func viewDidLoad() {
    super.viewDidLoad()
    NumSwitch.isOn = UserDefaults.standard.bool(forKey: "switchState")
    // Do any additional setup after loading the view, typically from a nib.
}


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

However when I run this code I get:

Thread 1: EXC_BAD_INSTRUCTION(code=EXC_1386_INVOP,subcode=0x0)

(Highlighting the line: 'NumSwitch.isOn = UserDefaults.standard.bool(forKey: "switchState")')

[I am using Xcode 8.2.1]

I have connected two UIViewControllers to one ViewController Class so maybe that is causing the problem. I have tried many many other methods to make my switch work properly and this one seems to have worked for other people. Is there anything obvious that I am doing wrong?

[I would have liked to have added this as a comment on the aforementioned question but I do not have the reputation to do so]

Answer 1

If everything is hooked up to your outlets correctly then the following should work:

@IBOutlet weak var NumSwitch: UISwitch!

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

    // If the below statement prints `nil` this is what's causing the crash
    print(NumSwitch)

    NumSwitch.setOn(isOn, animated: false)
}


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

The error Thread 1: EXC_BAD_INSTRUCTION(code=EXC_1386_INVOP,subcode=0x0) usually means that you're trying to force unwrap an optional value. The only thing that could be causing that in your code is if NumSwitch is nil.

I'd also suggest not naming your properties with capital letters, as this can be misleading. Capitalised names are usually used to indicate declared types/classes/structs etc.