How to remove a VC then add another VC directly afterward - ios

Question

I have a Main VC (call this VC A), that has a child VC (VC B). When I tap a button on VC B I dismiss it as a child VC, however once this is done I would like to instantiate another VC (VC C). I do this by creating a bool on VC B which, if true calls a function on VC A that creates a new child VC (VC C). All of the function calls are being made however the VC C never gets added. Below I have added the code:
VC B:
func removeAnimate()
{
self.willMove(toParentViewController: nil)
self.view.removeFromSuperview()
self.removeFromParentViewController()
didTransition = true
if didTransition == true {
callAddVC()
}
}
func callAddVC() {
let instVC = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "MainViewController") as! MainViewController
instVC.addVC()
}
VC A:
func addVC () {
let popvc = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "CommentsTabViewController") as! CommentsTabViewController
self.addChildViewController(popvc)
popvc.view.center = self.view.center
popvc.view.bounds.size = CGSize(width: 337, height: 503)
self.view.addSubview(popvc.view)
popvc.didMove(toParentViewController: self)
}

Answer 1

You are creating new instance of ViewController A (MainViewController) on the callAddVC(), Which is wrong. You are not using existing instance of the ViewController A
You have to pass the Viewcontroller A instance while adding a Viewcontroller B
Viewcontroller A
let viewControllerB = // Get the instance of UIViewControllerB from storyboard
viewControllerB.vcA = self
Viewcontroller B
class UIViewControllerB {
weak var vcA: UIViewControllerA?
func removeAnimate() {
self.willMove(toParentViewController: nil)
self.view.removeFromSuperview()
self.removeFromParentViewController()
didTransition = true
if didTransition == true {
vcA.addVC(). //You have to call addVC() by using the reference of the main view controller.
}
}
}

Answer 2

let instVC = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "MainViewController") as! MainViewController
This line creates (instantiates) a NEW instance of your MainViewController, it is not your current, displayed MainViewController.
You need to maintain a reference to the first MainViewController (possibly by accessing the rootViewController on the main window. And add the new popover to that.