如何在Swift中为自定义segue设置哪个ViewController在顶部？

Question

我正在尝试进行自定义设置，该设置与Xcode中默认设置的设置相反（这是从下到上）。我的意思是，我希望当前的VC消失，而我一直认为要支持它的VC。问题是，在我当前的代码中，VC过渡到顶部，因此我的segue不显示动画，因为它隐藏在该VC后面。如何拥有它，以使当前的VC处于最佳状态？

我的代码：

override func perform() {
    animateDown()
}

func animateDown() {
    var firstVCView = self.source.view
    var secondVCView = self.destination.view

    // Get the screen width and height.
    let screenWidth = UIScreen.main.bounds.size.width
    let screenHeight = UIScreen.main.bounds.size.height

    // Specify the initial position of the destination view.
    secondVCView!.frame = CGRect(x: 0, y: 0, width: screenWidth, height: screenHeight)

    // Access the app's key window and insert the destination view above the current (source) one.
    let window = UIApplication.shared.keyWindow
    window?.insertSubview(secondVCView!, aboveSubview: firstVCView!)

    // Animate the transition.
    UIView.animate(withDuration: 2, animations: { () -> Void in
        secondVCView!.frame = firstVCView!.frame.offsetBy(/*secondVCView!.frame, */dx: 0.0, dy: screenHeight)

    }) { (Finished) -> Void in
        self.source.present(self.destination as! UIViewController,
                                                        animated: false,
                                                        completion: nil)
    }
}