Call function from child to parent in Swift

Question

I am using xlpagertabstrip and I have a parent view controller which has two children (child1, child2).

In my parent view controller, I show a UIActivityViewIndicator but I want to know how to hide that indicator in my child1.

This is my code:

ParentViewController:

override func viewDidLoad() {
       showActivityIndicator()
       super.viewDidLoad()
}

func showActivityIndicator() {
    //code related to titleview
    navigationItem.titleView = titleView
}

func hideActivityIndicator() {
    navigationItem.titleView = nil
}

Child1ViewController:

override func viewDidLoad() {
    super.viewDidLoad()
    call_api()
}

func call_api(){
    //code related to api
    //if api is ok, I call hideActivityIndicator()
    let pctrl = ParentViewController()
    pctrl.hideActivityIndicator()
}

But that code does not work. How can I solve that?

`let pctrl = ParentViewController()`That's creating a WHOLE NEW object. That's not the one you think of. You could use Delegate Pattern or Closure to tell your parent to do something. — Larme, Oct 02 '18 at 16:26

Pato Salazar · Answer 1 · 2018-10-02T16:57:05.497

1

Just pass hideActivityIndicator() from the parent to the child and call it when necessary. So whenever you create your child controller do this:

// Parent Controller

childVC.someMethodFromParent = hideActivityIndicator

And in your ChildController do this:

// Child Controller

internal var someProperty: (() -> Void)!

override func viewDidLoad() {
    super.viewDidLoad()
    call_api()
}

func call_api(){
    //code related to api
    //if api is ok, I call hideActivityIndicator()

   someMethodFromParent()
}

This should work

edited Oct 02 '18 at 16:57

answered Oct 02 '18 at 16:28

Pato Salazar

1,447
12
21

Hi thanks for your answer, the idea is this: in my child when the api finish to be called the method hideactivityindicator() should works, I copy your answer but I have error – Israel Oct 02 '18 at 16:35
I get this Cannot assign to property: 'someMethodFromParent' is a method – Israel Oct 02 '18 at 16:42
I just copy your answer – Israel Oct 02 '18 at 16:49
change 'let' to `var` when defining `someMethodFromParent ` – Pato Salazar Oct 02 '18 at 16:51
what is someProperty var?, I think that I should define the someMethodFromParent as fun someMethodFromParent(){} – Israel Oct 02 '18 at 16:52
in you child controller put this `internal var someProperty: (() -> Void)!` – Pato Salazar Oct 02 '18 at 16:55
and when you create your child controller in your parent, assing the parent method into the child property like this ```childVC.someMethodFromParent = hideActivityIndicator``` – Pato Salazar Oct 02 '18 at 16:56
I have updated my answer to make it more clear and less ambiguous – Pato Salazar Oct 02 '18 at 16:58
but I should declare someMethodFromParent() as func? – Israel Oct 02 '18 at 17:02
yeah just declare a method in your parent the same way you would do it normally in you case would be this ```func hideActivityIndicator() { navigationItem.titleView = nil } ``` – Pato Salazar Oct 02 '18 at 17:08
Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/181175/discussion-between-israel-and-pato-salazar). – Israel Oct 02 '18 at 17:15
I invite you to chat, please help me – Israel Oct 02 '18 at 17:21

Sunil Chauhan · Answer 2 · 2021-02-15T15:57:51.630

1

How about having a ChildViewControllerDelegate? Something like:

class ParentViewController {
    func someFunc(){
        ...
        childVC.delegate = self
        ...
    }
}

extension ParentViewController: ChildViewControllerDelegate {
    func childViewControllerDidFinishApiCall() {
        hideActivityIndicator()
    }
}

protocol ChildViewControllerDelegate: class {
    func childViewControllerDidFinishApiCall()
}

class ChildViewController {
    weak var delegate: ChildViewControllerDelegate?

    func call_api(){
        //code related to api
        let pctrl = ParentViewController()
        delegate?.childViewControllerDidFinishApiCall()
    }
}

edited Feb 15 '21 at 15:57

answered Oct 02 '18 at 17:31

Sunil Chauhan

2,074
1
15
33

I get this error 'weak' may only be applied to class and class-bound protocol types, not 'ChildViewControllerDelegate' – Israel Oct 02 '18 at 18:14
oh, yes, see my updated answer: have `: class` in `ChildViewControllerDelegate` definition. – Sunil Chauhan Oct 02 '18 at 18:16
I do all your answer but does not work, the hideActivityIndicator() not works – Israel Oct 02 '18 at 18:37
I don't have errors but never is called the method hideActivityIndicator() – Israel Oct 02 '18 at 18:42

Call function from child to parent in Swift

2 Answers2