Pass variable to other view controller via back button

Question

I have two view controllers. One is navigated to with a "show" segue. There is a back button in the UINavigationBar that I have not changed. The back button goes back to the initial view controller. In the view controller with the back button, I am storing data in a variable.

How can I pass this data to my initial view controller?

I have tried:

viewWillDisappear(_ animated: Bool) {
    let vc = ViewController()
    vc.data = items
}

but the data in the initial view controller is empty when printed.

I've attempted to use:

prepare(for segue: ...)

but I'm not sure what segue the back button uses.

I can't seem to add an action of the back button to my view controller either.

Answer 1

You could use a delegate. First, create a protocol:

protocol getItemsDelegate {
    func getItems(_ items: [String])
}

In your first view controller's class definition add getItemsDelegate:

class myFirstViewController: UIViewController,getItemsDelegate

Add this to the prepare method in your first view controller:

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    let vc = segue.destination as! mySecondViewController
    vc.delegate = self
}

Lastly, in your first view controller, add this:

func getItems(_ items: [String]) {
    // Do something with items
}

In your second view controller, declare the following property:

var delegate: getItemsDelegate?

Then:

override func viewWillDisappear(_ animated: Bool) {
   delegate?.getItems(items)
}

This is just another way to do it.