How do you share data between view controllers and other objects in Swift?

Question

Say I have multiple view controllers in my Swift app and I want to be able to pass data between them. If I\'m several levels down in a view controller stack, how do I pass d

Answer 1

SWIFT 3:

If you have a storyboard with identified segues use:

func prepare(for segue: UIStoryboardSegue, sender: Any?)

Although if you do everything programmatically including navigation between different UIViewControllers then use the method:

func navigationController(_ navigationController: UINavigationController, willShow viewController: UIViewController, animated: Bool)

Note: to use the second way you need to make your UINavigationController, you are pushing UIViewControllers on, a delegate and it needs to conform to the protocol UINavigationControllerDelegate:

   class MyNavigationController: UINavigationController, UINavigationControllerDelegate {

    override func viewDidLoad() {
        self.delegate = self
    }

    func navigationController(_ navigationController: UINavigationController, willShow viewController: UIViewController, animated: Bool) {

     // do what ever you need before going to the next UIViewController or back
     //this method will be always called when you are pushing or popping the ViewController

    }
}

Answer 2

It depends when you want to get data.

If you want to get data whenever you want, can use a singleton pattern. The pattern class is active during the app runtime. Here is an example of the singleton pattern.

class AppSession: NSObject {

    static let shared = SessionManager()
    var username = "Duncan"
}

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()

        print(AppSession.shared.username)
    }
}

If you want to get data after any action, can use NotificationCenter.

extension Notification.Name {
    static let loggedOut = Notification.Name("loggedOut")
}

@IBAction func logoutAction(_ sender: Any) {
    NotificationCenter.default.post(name: .loggedOut, object: nil)
}

NotificationCenter.default.addObserver(forName: .loggedOut, object: nil, queue: OperationQueue.main) { (notify) in
    print("User logged out")
}