how to set variables on back press in navigationController swift? - ios

Question

According to this link , I wanted to pass some data from a B viewController to its parent, A viewController, on back press! here is my code :
in my B viewController, I've added this code -
extension Bcontroller: UINavigationControllerDelegate {
func navigationController(_ navigationController: UINavigationController, willShow viewController: UIViewController, animated: Bool) {
(viewController as? Acontroller)?.number = numberInB
(viewController as? Acontroller)?.myBoolean = boolInB
}
}
and here is my code in A controller :
override func viewWillAppear(_ animated: Bool) {
if number != -1 {
print(myBoolean)
}
}
when I open B controller, navigationController (willShow) is called, and when I press back button, viewWillAppear is called first, and then navigationController(willShow) in B controller is called! so my data is not set, and number will be always -1 . how can I set these variable?

Answer 1

Please find the below steps to implement delegate.
Step 1:- Initialise the protocol in view controller B.
ViewcontrollerB.m
protocol ViewControllerDelegate
{
func didUpdateViewController(_ number: NSNumber, myBoolean: Bool);
}
Step 2:-
initalise object inside viewcontrollerB
var delegate:ViewControllerDelegate?
Step 3:-
Now call this delegate from back function.Here I am considering back is the function to pop viewcontroller.
func Back()
{
delegate?.didUpdateViewController(numberInB!, myBoolean: boolInB!)
}
Step 4:-
Inherit the protocol in viewcontrollerA.
class ViewControllerA: UIViewController,ViewControllerDelegate
Step 5:-
Now Set the delegate in viewcontrollerA.
ViewcontrollerA.m
override func viewDidLoad() {
super.viewDidLoad()
let obj = ViewControllerB()//Initialize it as per your code
obj.delegate = self;
// Do any additional setup after loading the view, typically from a nib.
}
Final Step:-
override the delegate method.
func didUpdateViewController(_ number: NSNumber, myBoolean: Bool) {
print(number,myBoolean)
}
Let me know if it worked

Answer 2

Do call it in viewWillDisappear of controller B:
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(true)
let navigationController: UINavigationController = self.navigationController!
let controllers: [Acontroller] = navigationController.viewControllers.filter({ $0 is Acontroller }) as! [Acontroller]
if let viewController: Acontroller = controllers.first {
viewController.number = numberInB
viewController.myBoolean = boolInB
}
}
If the controller is in stack the values will be assigned to it.

Answer 3

If it is a small data then use UserDefaults:
This is how you store data:
UserDefaults.standard.set(1, forKey: "Key")
And this is how you get it back:
UserDefaults.standard.integer(forKey: "Key")
Or you can use a struct with a static variable:
struct ShareValue {
static var UserNum: Int = 0
}

Answer 4

Create a delegate which other view controllers can implement and call the delegate method in viewWillDisappear when isMovingFromParentViewController is true
public protocol YourViewControllerDelegate: class {
func didGoBack(viewController: YourViewController)
}
public class YourViewController: UIViewController {
public weak var delegate: YourViewControllerDelegate?
public override func viewWillDisappear(_ animated: Bool) {
if isMovingFromParentViewController {
delegate?.didGoBack(viewController: self)
}
}
}
In your other view controller:
extension YourOtherViewController: YourViewControllerDelegate {
public func didGoBack(viewController: YourViewController) {
// Do something e.g. set your variables
}
}