change label from another viewcontroller on swift - ios

Question

I want to change label from another viewController.
First viewcontroller is MenuController. Second one is LoginViewController.
I want to change MenuController's Label.text from LoginViewController.
In LoginViewController:
let viewController = MenuController()
viewController.changeLabel("logout")
In MenuController:
class MenuController: UITableViewController {
var attractionImages = [String]()
var attractionNames = [String]()
var webAddresses = [String]()
#IBOutlet weak var loginLabel: UILabel!
override func viewDidLoad() {
super.viewDidLoad()
loginLabel.text = "Login"
print(loginLabel.text)
}
func changeLabel(Log: String)O {
self.loginLabel.text = log
print (log)
}
But an error occur.
fatal error: unexpectedly found nil while unwrapping an Optional value
How can I solve it?
Thanks for your help.

Answer 1

Another way to achieve that is you can use NSNotificationCenter. Blow is the example for that:
In your MenuController add this code:
override func viewDidLoad() {
super.viewDidLoad()
NSNotificationCenter.defaultCenter().addObserver(self, selector: "refreshLbl:", name: "refresh", object: nil)
}
Also add this helper method:
func refreshLbl(notification: NSNotification) {
print("Received Notification")
lbl.text = "LogOut"
}
Now in your LoginViewController your back button action will look like:
#IBAction func back(sender: AnyObject) {
NSNotificationCenter.defaultCenter().postNotificationName("refresh", object: nil, userInfo: nil)
self.dismissViewControllerAnimated(true, completion: nil)
}
Now when ever you press back button from LoginViewController your refreshLbl method will call from MenuController.
For more info refer THIS example.

Answer 2

Swift 3 version:
In your MenuController (where the label needs to be changed) add this code:
override func viewDidLoad() {
super.viewDidLoad()
NotificationCenter.default.addObserver(self,
selector: #selector(refreshLbl),
name: NSNotification.Name(rawValue: "refresh"),
object: nil)
}
Also add this helper method:
#objc func refreshLbl() {
print("Received Notification")
lbl.text = "LogOut"
}
Now in your LoginViewController your back button action will look like:
#IBAction func backButton(_ sender: Any) {
NotificationCenter.default.post(name: NSNotification.Name(rawValue: "refresh"), object: nil)
// Any additional code...
}
Now when ever you press back button from LoginViewController your refreshLbl() method will call from MenuController.