viewdidappear not called when adding subview to navigation controller

Question

func showCustomViewController(vc : UIViewController,dummy : UIView,fromView1:UIViewController){
    datePickerShown = true
    let fromView = fromView1.navigationController?.view
    var navTopConstraint : NSLayoutConstraint!
    vc.view.translatesAutoresizingMaskIntoConstraints=false

    self.navigationController?.addChildViewController(vc)
    dummy.addSubview(vc.view)
    vc.didMove(toParentViewController: self.navigationController)

    dummy.addConstraint(NSLayoutConstraint(item: vc.view, attribute: .top, relatedBy: .equal, toItem: dummy, attribute: .top, multiplier: 1, constant: 0))
    dummy.addConstraint(NSLayoutConstraint(item: vc.view, attribute: .left, relatedBy: .equal, toItem: dummy, attribute: .left, multiplier: 1, constant: 0))
    dummy.addConstraint(NSLayoutConstraint(item: vc.view, attribute: .width, relatedBy: .equal, toItem: dummy, attribute: .width, multiplier: 1, constant: 0))
    dummy.addConstraint(NSLayoutConstraint(item: vc.view, attribute: .height, relatedBy: .equal, toItem: dummy, attribute: .height, multiplier: 1, constant: 0))
    dummy.backgroundColor=UIColor.clear

    if dummy.superview == nil{
        fromView?.addSubview(dummy)
    }

    for constraints in dummy.constraints{
        if constraints.firstAttribute == .top{
            navTopConstraint = constraints
        }
    }

    fromView?.addConstraint(NSLayoutConstraint(item: dummy, attribute: .width, relatedBy: .equal, toItem: fromView, attribute: .width, multiplier: 1, constant:0 ))
    fromView?.addConstraint(NSLayoutConstraint(item: dummy, attribute: .top, relatedBy: .equal, toItem: fromView, attribute: .top, multiplier: 1, constant: -60))
    fromView?.addConstraint(NSLayoutConstraint(item: dummy, attribute: .bottom, relatedBy: .equal, toItem: fromView, attribute: .bottom, multiplier: 1, constant: 0))
    fromView?.addConstraint(NSLayoutConstraint(item: dummy, attribute: .left, relatedBy: .equal, toItem: fromView, attribute: .left, multiplier: 1, constant: 0))

    navTopConstraint.constant = (fromView?.frame.maxY)!
    fromView?.layoutIfNeeded()

    UIView.animate(withDuration: 0.33, delay: 0, options:.curveEaseInOut, animations: {
        dummy.backgroundColor=UIColor.init(white: 0.0, alpha: 0.4)
        navTopConstraint.constant=0
        fromView?.layoutIfNeeded()
    }, completion: nil)
}

dummy view is the uiview added to the current navigation controller view. vc is the viewcontroller to be added to the navigation controller view. In vc viewcontroller, viewdidload is called. But viewdidappear and viewwillappear is never called.why is it so? and how to call the same.Thanks in advance

Answer 1

According to Apple's documentation the order you added the view controller and view is correct, however, sometimes there seems to be a bug when you add the view controller before adding the view (possibly some sort of race condition).

Try adding the view first before adding the controller as child view controller

dummy.addSubview(vc.view)
self.navigationController?.addChildViewController(vc)

You could maybe also try to wrap the addChildViewController() method inside a defer block.