How I can transfer data between controllers when returning to the last screen? Swift

Question

In the application, I am asked to select a category, when I click, I move to the next screen from the tableView, and when I click on the desired category, it should be saved and return to the previous controller, where instead of "select a category" my chosen category will be.

I using by this method navigationController?.popViewController(animated: true), which brings me back to the last screen. As I understand it, prepare is not called, but since I know exactly where I'm going, I can, in the method from which I call pop ..., get access to the controller I am switching to and pass it the necessary properties? But how?

override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
  let currentCell = categories[indexPath.row]
    /?
    /?
  navigationController?.popViewController(animated: true)
}

check this: https://stackoverflow.com/questions/19343519/pass-data-back-to-previous-viewcontroller — Andreas Oetjen, May 08 '19 at 13:19
Possible duplicate of [Pass data back to previous viewcontroller](https://stackoverflow.com/questions/19343519/pass-data-back-to-previous-viewcontroller) — Daniyar, May 08 '19 at 13:23
You can use closures to solve that. Refer https://stackoverflow.com/a/56075711/5716829 — PGDev, May 10 '19 at 10:50

Shehata Gamal · Accepted Answer · 2019-05-08T16:27:12.297

3

When you go to the select screen do

let vc = ///
vc.delegate = self
// push

then inside didASelectRowAt

class CategoryViewController:UIViewController {
 weak var delegate:PreviousVC?
 ////
}

delegate?.sendData(someData)
navigationController?.popViewController(animated: true)

Another option inside didASelectRowAt to

// access previous vc
let previousVC = self.navigationController!.viewControllers[self.navigationController!.viewControllers.count - 2] as! PreviousVc
previousVC.sendData(someData)
// pop here

Edit: inside the firstVC

     override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if let secondVC = segue.destination as? SecondViewController {
          secondVC.delegate = self   
        }
    }

edited May 08 '19 at 16:27

answered May 08 '19 at 13:21

Shehata Gamal

98,760
8
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I can't do vc.delegate = self "Value of type 'CategoryViewController' has no member 'delegate'" – Mikhail Tseitlin May 08 '19 at 13:34
replace `PreviousVC` with your own name and see edit of `CategoryViewController` – Shehata Gamal May 08 '19 at 13:37
Why then during the transition the data does not change ... let currentCell = categories[indexPath.row] delegate?.defaultTransaction.category = currentCell navigationController?.popViewController(animated: true) – Mikhail Tseitlin May 08 '19 at 14:03
verified delegate is not nil with `delegate!` – Shehata Gamal May 08 '19 at 14:04
What do you mean? – Mikhail Tseitlin May 08 '19 at 14:09
try `delegate!.defaultTransaction.category = currentCell ` – Shehata Gamal May 08 '19 at 14:10
Fatal error: Unexpectedly found nil while unwrapping an Optional value – Mikhail Tseitlin May 08 '19 at 14:16
do you assigned the delegate ? also do you have a segue ? – Shehata Gamal May 08 '19 at 14:19
Yes. In prepare segue (firstVC) I created let vc/// vc.delegate = self and in secondVC I created weak var delegate: FitstVC? and in method didSelectedRowAt trying to transfer the data – Mikhail Tseitlin May 08 '19 at 14:22
but when I trying to transfer data I getting nil – Mikhail Tseitlin May 08 '19 at 14:57
delegate?.sendData(someData) == nil – Mikhail Tseitlin May 09 '19 at 05:48
So finally, I did it! But I used == let vc = self.storyboard?.instantiateViewController(withIdentifier: "AddTransactionViewController") as? AddTransactionViewController { vc.defaultTransaction.category = currentCell navigationController?.pushViewController(vc, animated: true) – Mikhail Tseitlin May 09 '19 at 06:15

score 0 · Answer 2 · answered May 08 '19 at 13:26

You can pass the selected category to the previous view controller using closure

class FirstViewController: UIViewController {   
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if let secondVC = segue.destination as? SecondViewController {
            secondVC.selectedOption = { selectedOption in
                print(selectedOption)
                //change category title here
            }
        }
    }

}
class SecondViewController: UIViewController {
    var selectedOption: ((String) -> Void)?
    func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        selectedOption?("Selected Option String")
        navigationController?.popViewController(animated: true)
    }
}

score 0 · Answer 3 · answered May 08 '19 at 13:38

0

Maybe you should pass "Completion handler" when you move to your category selection controller like

(String)->(Void)

and when you pop it, pass your category in this clouser

answered May 08 '19 at 13:38

Ilya Stukalov

101
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3

How I can transfer data between controllers when returning to the last screen? Swift

3 Answers3