Is it fine to nest a UIViewController within another without using addChildViewController?

Question

I'm trying to make a custom ContainerViewController, but due to lots of difficulties with the ViewController transitions and making everything interactive, I've decided to mimic that functionality myself.

What I basically want to do, is have a paginated UIScrollView (the HeaderView) on the top control different another UIScrollView (the ControllersView) below that contains ViewControllers as pages so that as you swipe to a new page on the HeaderView, it also swipes to the next viewcontroller on the ControllersView. This is what the setup would look like.

My question is, is there anything wrong with having the aforementioned setup? All I'll do to add the view controllers to the ControllersView is just something like: controllersView.addSubview(pagecontroller1.view).

Some posts online seem to say that "the appropriate ViewController functions won't be called" or whatever. What do I seem to be missing here? I'm guessing there's a lot of dismissing and admitting of ViewControllers that I need to call every time a ViewController is out of frame right?

To clarify the question: Is it ok/efficient to do this? Should I be calling some viewWillAppear/disapper functions when the VC's get in and out of frame? If so, what should I call? I'm realizing that if I were to set things up this way, I need to manage a lot of things that are usually handled automatically, but as I mentioned before, custom ContainerViewControllers have failed me and I'm going with this.

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PS. If you seem to still be lost on how this will look like, see my previous question here where I originally wanted to use a Container ViewController. There's a much better mockup there.

Answer 1

You can add and remove VC In Container Views

For - Is it ok/efficient to do this? Should I be calling some viewWillAppear/disapper functions when the VC's get in and out of frame? If so, what should I call?

As, We need to call WillAppear and Disappear Func when Adding and removing a VC , Thus Try using below Functions That will Handle these Responses

I use the Two specific Functions to add and remove Controller in ContainerView/UIView/SubView in ScrollView inside a UIView

To Add

private func add(asChildViewController viewController: UIViewController)
{
    // Configure Child View
    viewController.view.frame = CGRect(x: 0, y: 0, width: self.firstContainer.frame.size.width, height: self.firstContainer.frame.size.height)

    // Add Child View Controller
    addChildViewController(viewController)
    viewController.view.translatesAutoresizingMaskIntoConstraints = true

    // Add Child View as Subview
    firstContainer.addSubview(viewController.view)

    // Notify Child View Controller
    viewController.didMove(toParentViewController: self)
}

To Remove

private func remove(asChildViewController viewController: UIViewController)
{
    // Notify Child View Controller
    viewController.willMove(toParentViewController: nil)

    secondContainer.willRemoveSubview(viewController.view)

    // Remove Child View From Superview
    viewController.view.removeFromSuperview()

    // Notify Child View Controller
    viewController.removeFromParentViewController()
}

Creating Object

private lazy var FirstObject: firstVC =
  {
    // Instantiate View Controller
    let viewController = self.storyboard?.instantiateViewController(withIdentifier: "firstVC") as! firstVC

    // Add View Controller as Child View Controller
    self.addChildViewController(viewController)
    return viewController
  }()

For - controllersView.addSubview(pagecontroller1.view)

Answer - Yes Approbate func wont be called if pagecontroller1 is not loaded in to memory stack, to load that you need to notify pagecontroller1 that it is going to be added to memory stack as Child View , Just as We initiate a Controller and basically notifies the Controller to get its component loaded to memory stack to get some memory allocations

For Question - Is it fine to nest a UIViewController within another without using addChildViewController?

Check apple Documentation - https://developer.apple.com/documentation/uikit/uiviewcontroller/1621394-addchildviewcontroller

This is necessary just as to notify the controller who is going to be added in Another Parent View as Child

Sample Project

https://github.com/RockinGarg/Container_Views.git

Or

https://github.com/RockinGarg/ContainerView-TabBar.git

If Question is Still not answered Please Tell me what Func Exactly you want to handle by yourself