iOS / Swift 3：在不连续的View Controller之间向后传递数据

Question

I know there are answers for passing data backwards, but they are for consecutive view controllers. I have 3 view controllers and a navigation controller. All segues are "show segue". I would like to pass data from VC3 to VC1. I'm trying to use delegate, but getting stuck:

    protocol Delegate:class {
        func getCityId(with id: String)
    }


    Class VC3:UIViewController{
     weak var delegate: Delegate?
    let id:String?

     func passDataBackwards() {

            delegate?.getCityId(with: self.id!)

    }

  }  
    Class VC1:UIViewController, Delegate{
     func getCityId(with id: String) {
            print ("id from search: \(id)")

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        let vc3 = (segue.destination as! VC3)
          vc3.delegate = self
       }
   }

My problem is that I have 2 segues between my source and destination. Your kind help will be appreciated.

Answer 1

You can use an unwind segue as shown in this Apple Tech Note .

In your storyboard, create an Unwind segue as shown in the tech note and give it an identifier, say "unwindToVC1"

In VC3, create a property to store the selected value and use performSegue in your table's didSelectRowAt function to invoke it, having first stored the selected value in the property:

class VC3: UIViewController {

   var selectedValue: YourValueType?

   func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
       self.selectedValue = myData[indexPath.row]
       self.performSegue(withIdentifier: "unwindToVC1", sender: self)
    }
}

Create an unwind action method in VC1 and access the property

class VC1: UIViewController {

    @IBAction func unwind(sender: UIStoryboardSegue) {
        if let sourceVC = sender.sourceViewController as? VC3 {
            if let selectedValue = sourceVC.selectedValue {
                // Do something with the selected value
            }
        }
    }
}

Now you can have any number of view controllers between the current VC and VC1 and get back to it with a simple unwind segue.