Swift: How to access in AppDelegate variable from the View controller?

Question

I would like to write in the text or csv (prefer) file the variable from the view controller.

Indeed I am doing a drawing app and I would like to write in the file the current position of the finger.

class ViewController: UIViewController {var lastPoint = CGPoint.zeroPoint ... }

I would like to have access to lastPoint.x and lastPoint.y from the AppDelegate. how I could do that ? Thank you.

Answer 1

Your question is full of confusion but if that's what you are looking for:

You can access the appDelegate by getting a reference to it like that:

let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate

after that if you have store a property called lastPoint in your appDelegate you can access its components very simply like that:

let x = appDelegate.lastPoint.x
let y = appDelegate.lastPoint.y

If you need to access your viewController properties from the AppDelegate, then I suggest having a reference to your view controller in your appdelegate:

var myViewController: ViewController!

then when your view controller is created you can store a reference to it in the appdelegate property:

If your create your view controller outside of your appDelegate:

Swift 1-2 syntax

var theViewController = ViewController()
let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
appDelegate.myViewController = theViewController

Swift 3-4 syntax

var theViewController = ViewController()
let appDelegate = UIApplication.shared.delegate as! AppDelegate
appDelegate.myViewController = theViewController

If you create your view controller inside of your appDelegate:

self.myViewController = ViewController()

After that you can access your data from your viewcontroller from your appdelegate just by accessing its property like that:

let x = self.myViewController.lastPoint.x
let y = self.myViewController.lastPoint.y

Answer 2

I did manage to access my ViewController from the App delegate by creating an instance of ViewController in AppDelegate.swift, like:

var mainViewController = ViewController()

func applicationWillEnterForeground(_ application: UIApplication) {
    mainViewController.myVariable = "Hello".
}

Still, I don't understand how does the AppDelegate "know" that mainViewController is supposed to point to that particular ViewController. As my application has a single view and a single ViewController, that's fine, but what it I had multiple ViewControllers associated with different UIViews? Appreciate if anyone here can shed a light into that. Best Regards, Andre

Answer 3

Swift 3 Update

    var theViewController = ViewController()
    let appDelegate = UIApplication.shared.delegate as! AppDelegate
    appDelegate.myViewController = theViewController

Answer 4

You can create a BaseViewController and write this

class BaseViewController {
  lazy var appDelegate : AppDelegate {
     return UIApplication.shared.delegate as? AppDelegate
  }
}

and inherit other viewcontrollers with BaseViewController and access this by

class ViewController : BaseViewController {

override func viewDidLoad() {
    super.viewDidLoad()
    print(self.appDelegate?.lastPoint.x)
    print(self.appDelegate?.lastPoint.x)
}}