将子视图添加到导航控制器时未调用viewdidappear

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)
}

虚拟视图是添加到当前导航控制器视图的uiview . vc是要添加到导航控制器视图的viewcontroller . 在vc viewcontroller中，调用viewdidload . 但是viewdidappear和viewwillappear永远不会被调用 . 为什么会这样？以及如何打电话 . 谢谢