How to access the child view controller from parent view controller in swift?

Question

I have a view controller which has a child view controller and I want to access that child view controller from its parent view controller.

How can I achieve that?

Answer 1

The answer is ... (drum-roll......) ... it depends.. :-)

NSViewController & UIViewController have a .parent property. https://developer.apple.com/documentation/uikit/uiviewcontroller/1621362-parent https://developer.apple.com/documentation/appkit/nsviewcontroller/1434491-parent

However, it is only populated if you're implementing the container-view-controller design pattern: https://developer.apple.com/library/archive/featuredarticles/ViewControllerPGforiPhoneOS/ImplementingaContainerViewController.html (many uikit components use this pattern) IE:

aViewController.addChild(bViewController)
bViewControler.didMove(toParent: aViewController)
bViewController.parent // is aViewController

* Note: you'll have to manage the view stack yourself, this just ensures things like the lifecycle/drawing/resize/etc handlers happen in the correct order

If you need to retain a reference to a view controller (child or otherwise), create a property on the child and set a reference to it, or use the container-view-controller design, it's very useful.

Cheers
- J

Answer 2

There are many ways but for simply explanation I think this example will be instructive for you.

Suppose that you are trying to achieve navigate your viewcontrollers and using navigation controller for that in a stack

   let parentVC = UIViewController()
   let childVC = UIViewController()

   parentVC.navigationController?.viewControllers.append(childVC)
   let childVCisHere = parentVC.navigationController?.viewControllers.first

Finally think about the analogy I established on - GodFather - family hieararchy

Don Vito Corleone , he is the boss also father of the family parentVC

Sonny Corleone , he is dealing with dirty jobs, navigate childs behalf of family navigationController

Michael Corleone , he is little bro, people see him on the screen mostly :) childVC