Fatal Error while call method from another class - ios

Question

I have two view controller.
I have one test method in first view controller as follow
class ViewController: UIViewController {
#IBOutlet weak var myLabel: UILabel!
override func viewDidLoad() {
super.viewDidLoad()
myLabel.hidden = true
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
}
func showLabel(){
myLabel.hidden = false
}
}
If i call showLabel from another class it give me fatal error: unexpectedly found nil while unwrapping an Optional value
Another viewController is as follow
class SecondViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
}
#IBAction func Save(sender: AnyObject) {
ViewController().showLabel()
}
}
If i call showLabel Method from ViewController the its works fine but if i call it from SecondViewController then i got error.

Answer 1

Both your view controllers use storyboard/xib; when you create such view controller instance in code (as you do in Save function) you need use UINib class or instantiateViewControllerWithIdentifier method of UIStoryboard class, since default initializers (like init() you used for ViewController) know nothing about outlets and storyboard/xib associated files (outlet property myLabel will always be nil).
If your code not just template, then you should refactor it, because performing UI changes in view controller that not presented on screen (and never will be) not have sense

Answer 2

It's because your label "myLabel" is always nil.
Your label is part of your first ViewController. The label loads when the view loads. Since the ViewController view has not loaded, the label has not loaded either, and therefore will be nil

Answer 3

You need use delegate:
1-Creat a protocol with a function describes with you are planning to do.
protocol ViewControllerDelegate: AnyObject {
func showLabel()
}
2-Add a delegate in your SecondViewController with the type if the protocol ViewControllerDelegate.
class SecondViewController: UIViewController {
weak var delegate: ViewControllerDelegate? // add delegate
override func viewDidLoad() {
super.viewDidLoad()
}
#IBAction func Save(sender: AnyObject) {
delegate?.showLabel() // call the method from delegate
}
}
3-Implement the ViewControllerDelegate in your ViewController.
class ViewController: UIViewController, ViewControllerDelegate {
3-Set the delegate in the first view controller inside prepareForSegue:
class ViewController: UIViewController {
#IBOutlet weak var myLabel: UILabel!
override func viewDidLoad() {
super.viewDidLoad()
myLabel.hidden = true
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
}
func showLabel(){
myLabel.hidden = false
}
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
if let viewController = segue.destinationViewController as? SecondViewController {
viewController.delegate = self
}
}
}

Answer 4

just add class before function:
class Math{
class func addition(numberOne: Int, numberTwo: Int) -> Int{
var ans: Int = numberOne + numberTwo
return ans
}
}
Then you can call it from another Swift class like this:
Math.addition(40, numberTwo: 2)
To assign it to a variable i:
let i = Math.addition(40, numberTwo: 2) // -> 42