Cannot take values from other view controller Swift - ios

Question

I want to take user settings details from this view controller and read these details to the previous view controller. I have tried many different ways, but I cannot take values until I visit this view controller
I have tried first method from this page Pass Data Tutorial
This method is also not working. I think it is very simple, but I cannot figure out the right way to do it.
class SetConvViewController: UIViewController {
var engS = "engS"
#IBOutlet weak var swithEnglish: UISwitch!
override func viewDidLoad() {
super.viewDidLoad()
if let eng2 = defaults.value(forKey: engS)
{
swithEnglish.isOn = eng2 as! Bool
}
}
let defaults = UserDefaults.standard
#IBAction func switchEng(_ sender: UISwitch) {
defaults.set(sender.isOn, forKey: engS)
}
}

Answer 1

If I understand you correctly from this part - „but I cannot take values until I visit this view controller” - your problem lies with the fact, that until you visit your settings, there is no value for them in UserDefaults.
If you are reading them using getObject(forKey:) method, I’d recommend you to switch to using getBool(forKey:), since it will return false even if the value has not been set yet for that key ( docs )
Anyhow, if you want to set some default/initial values you can do so in your didFinishLaunching method in AppDelegate :
if UserDefaults.standard.object(forKey: „engS”) == nil {
// the value has not been set yet, assign a default value
}
I’ve also noticed in your code that you used value(forKey:) - you should not do that on UserDefaults - this is an excellent answer as to why - What is the difference between object(forKey:) and value(forKey:) in UserDefaults?.
On a side note, if you are using a class from iOS SDK for the first time, I highly recommend looking through its docs - they are well written and will provide you with general understanding as to what is possible.

Answer 2

I would recommend you to store this kind of data as a static field in some object to be able to read it from any place. e.g.
class AppController{
static var userDefaults = UserDefaults.standard
}
and then you can save it in your SetConvViewController like
#IBAction func switchEng(_ sender: UISwitch) {
AppController.userDefaults.set(sender.isOn, forKey: engS)
}
and after that you can just read it from any other view controller just by calling
AppController.userDefaults

Answer 3

Using segues you can set to any destination whether it be next vc or previous:
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == "PreviousVC" {
if let prevVC = segue.destination as? PreviousViewController {
//Your previous vc should have your storage variable.
prevVC.value = self.value
}
}
If you're presenting the view controller:
Destination vc:
//If using storyboard...
let destVC = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "DestinationViewController") as! DestinationViewController
destVC.value = self.value
self.present(destVC, animated: true, completion: nil)
Previous vc:
weak var prevVC = self.presentingViewController as? PreviousViewController
if let prevVC = prevVC {
prevVC.value = self.value
}