viewDidAppear being called strangley

Question

I have a viewController containing segmentedControl. I have a VCA and VCB which are in the segmentedControl. When I tap on second segment VCB appears. Now I am pushing another ViewController from VCB. But when coming back from that viewController, viewDidAppear of VCA is being Called. Which is strange to me. Because user is on the VCB so why the viewWillAppear and viewDidAppear of VCA are being called ? Here is a diagram to explain more

This is how I am adding viewControllers to segmentedControl

 func switchToViewController(viewController: UIViewController, selectedIndex: Int) {

    viewController.removeFromParentViewController()
    viewController.view.removeFromSuperview()

    addChildViewController(viewController)
    viewController.view.translatesAutoresizingMaskIntoConstraints = false
    self.view.addSubview(viewController.view)

    // Setting constraints of the container view
    NSLayoutConstraint.activate([
    viewController.view.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 0),
        viewController.view.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: 0),
        viewController.view.topAnchor.constraint(equalTo: view.topAnchor, constant: 50),
        viewController.view.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: 0)
        ])

    viewController.didMove(toParentViewController: self)
}

I am just unable to understand the behavior. So please guide me.

is viewcontroller containing segmented control and VCA same ? — Priyal, May 08 '17 at 10:30
no They are not same. viewController containing segmentedControl is a different VC lets call it VCSegmentedControl — Asim Iftikhar Abbasi, May 08 '17 at 11:13
Why you are removing `viewController` and adding same `viewController`? — Karthick Selvaraj, May 08 '17 at 11:19
Actually I am using same function when user taps on a segment control. So I am removing it before adding it again otherwise it would add multiple times i think. — Asim Iftikhar Abbasi, May 08 '17 at 11:22
can you suggest any other scenario without changing the implementation — Asim Iftikhar Abbasi, May 08 '17 at 12:29

score 2 · Accepted Answer · answered May 08 '17 at 13:47

You are never removing the current view controller and its view from the hierarchy...

You need to keep track of which VC/view is currently displayed - perhaps with a currentVC variable, and your function should look something like this:

func switchToViewController(viewController: UIViewController, selectedIndex: Int) {

    // remove current ViewController from VC hierarchy
    currentVC.removeFromParentViewController()

    // remove current VC.View from View hierarchy
    currentVC.view.removeFromSuperview()

    // the "incoming" ViewController becomes the "current" ViewController
    currentVC = viewController

    addChildViewController(viewController)
    viewController.view.translatesAutoresizingMaskIntoConstraints = false
    self.view.addSubview(viewController.view)

    // Setting constraints of the container view
    NSLayoutConstraint.activate([
    viewController.view.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 0),
        viewController.view.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: 0),
        viewController.view.topAnchor.constraint(equalTo: view.topAnchor, constant: 50),
        viewController.view.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: 0)
        ])

    viewController.didMove(toParentViewController: self)
}

Karthick Selvaraj · Answer 2 · 2017-05-09T04:06:26.307

Here you go, you can achieve this by using containerView. ContainerView is a normal UIView subclass. Your UI will be like this. You will have one baseViewController where you will have segmentControl and containerView view in baseViewController.

Assume you have two view controller namely viewController1 and viewController2. You can add these viewControllers as childViewController to this containerView like below.

import UIKit

class BaseViewController: UIViewController {

    @IBOutlet weak var typeSegment: UISegmentedControl!
    @IBOutlet weak var containerView: UIView!

    var viewController1: UIViewController?
    var viewController2: UIViewController?


    // MARK: - Action method.

    @IBAction func segmentIndexChanged(_ sender: Any) {

        let selectedIndex = typeSegment.selectedSegmentIndex

        switch selectedIndex {
        case 0:
            addVC1()
        case 1:
            addVC2()
        default:
            break
        }

    }

func rectForChildVC() -> CGRect {

    let rect = CGRect(x: containerView.frame.origin.x , y: containerView.frame.origin.y, width: containerView.frame.size.width, height: containerView.frame.size.height)
    return rect

}

func addVC1() {

    removeVC2()
    let storyboard = UIStoryboard(name: "StoryboardName", bundle: nil)
    viewController1 = storyboard.instantiateViewController(withIdentifier: "Viewcontroller1Identifier") // Create you first view controller instance here.
    viewController1?.view.frame = rectForChildVC()
    addChildViewController(viewController1!)
    view.addSubview((viewController1?.view)!)
    viewController1?.didMove(toParentViewController: self)
    view.layoutIfNeeded()

}

func addVC2() {

    removeVC1()
    let storyboard = UIStoryboard(name: "StoryboardName", bundle: nil)
    viewController2 = storyboard.instantiateViewController(withIdentifier: "Viewcontroller2Identifier") // Create you second view controller instance here.
    viewController2?.view.frame = rectForChildVC()
    addChildViewController(viewController2!)
    view.addSubview((viewController2?.view)!)
    viewController2?.didMove(toParentViewController: self)
    view.layoutIfNeeded()

}

func removeVC1() { // Remove first view controller.

    if let viewController = viewController1 {
        viewController.didMove(toParentViewController: nil)
        viewController.view.removeFromSuperview()
        viewController.removeFromParentViewController()
    }

}

func removeVC2() { // Remove second view controller

    if let viewController = viewController2 {
        viewController.didMove(toParentViewController: nil)
        viewController.view.removeFromSuperview()
        viewController.removeFromParentViewController()
    }

}

}

Thanks.

Thanks for your solution but i don't want to change my implementation... :) — Asim Iftikhar Abbasi, May 09 '17 at 06:48

viewDidAppear being called strangley

2 Answers2