How to pass data to parent view controller

Question

I'm performing a segue on my parent VC when clicked on an image. I want to pass data back to the parent VC from child VC. I've been exploring various options to pass data back to parent VC but can't figure it out.

Since the child VC is part of Navigation and it's presented (show) via segue there should be an easy way to pass data back to parent.

How to do it?

I've tried viewWillDisappear method but parentVC is nil in following code.

override func viewWillDisappear(_ animated: Bool) {
    super.viewWillDisappear(animated)

    if self.isMovingFromParent {
        if let navVC = self.presentingViewController as? UINavigationController {
            if let parentVC = navVC.viewControllers.first as? ParentViewController {
                print("viewWillDisappear() moving to parent") // Not executed
                parentVC.data = self.data
            }
        }
    }
}

score 1 · Accepted Answer · answered Aug 22 '19 at 18:20

1

One strategy would be to set the parent as a delegate of the child. You would create this relationship in a prepare(for:sender:) function.

If you are unfamiliar with delegation, this article is a good guide: https://medium.com/@jamesrochabrun/implementing-delegates-in-swift-step-by-step-d3211cbac3ef

answered Aug 22 '19 at 18:20

Dancreek

9,524
1
31
34

I'm aware of delegate and I can get it working with delegates but this doesn't seem to be an elegant solution. Imagine if you 10 segues from one view, you will end up writing a lot of code to handle these delegates. Isn't it any easier way to utilise Navigation stack/segue control properties to pass data which will be much easier. – Oliver Aug 22 '19 at 18:27
1

It doesn't need to be much code. Just check for segueID and assign parent to child. 3 lines of code, max. Using the navigation stack is making some assumptions about what you'll find in that stack. Every time you need to send info back you'll have to check the stack and then see if its the right thing to send data back to. I would opt for the delegate method. – Dancreek Aug 22 '19 at 18:48

score 1 · Answer 2 · answered Aug 22 '19 at 18:41

1

Use delegate for sending data, back to the Parent.

answered Aug 22 '19 at 18:41

Trupti

284
5
7

score 1 · Answer 3 · answered Aug 22 '19 at 18:44

You can use 3 ways of assing data back from child to parent ViewController, as mentioned in previos answer you may use delegates, or clousures, but since you dont want to deal with

if segue.identifier == "segueIdentifier"

then you could use notifications, creating observer in the parent and then posting in the child view controller. in the parent

override func viewDidLoad(){
 NotificationCenter.default.addObserver(self, selector: #selector("yourSelectorName"), name: "NotificationName", object: nil)

and in the child post with this.

NotificationCenter.default.post(name: "notificationName", object: nil, userInfo: ["your data array "])

where notification name is not a string you must create a name for it and you may pass data or not in userInfo.

score 1 · Answer 4 · answered Aug 23 '19 at 08:00

Swift 5, Xcode 10.3

Use any 1 of below methods

1.Access reference of parentVC through self.navigationController.viewControllers and then use that reference to access variables and set data

2.you can use unwind segue

3.use delegate protocol

if you need more details, please refer https://stackoverflow.com/a/9736559/10579134

How to pass data to parent view controller

4 Answers4