push vs present

class ViewController:UIViewController {

     ....

     func showPopup(){
            let popupVc = AppDelegate.shared.getVC( "\(PopupViewController.self)")

             // 1. pushViewController
             //self.navigationController?.pushViewController( popupVc,  animated:true)

             // 2. present ViewController
             //self.present( popupVc, animated:true, completion:nil )
     }
}


1. pushViewController

ViewController disappeared. but navigationController manages this ViewController.




2. present ViewController

ViewController didn't disappear.
PopupViewController is stacked on the ViewController.
UIWindow has 2 UITransitionViews ( navigationController , PopupViewController )