基本思想是创建一个转换委托对象,该对象标识将用于自定义转换的动画控制器,交互控制器和表示控制器：

class TransitioningDelegate: NSObject,UIViewControllerTransitioningDelegate {

    /// Interaction controller
    ///
    /// If gesture triggers transition,it will set will manage its own
    /// `UIPercentDrivenInteractiveTransition`,but it must set this
    /// reference to that interaction controller here,so that this
    /// knows whether it's interactive or not.

    weak var interactionController: UIPercentDrivenInteractiveTransition?

    func animationController(forPresented presented: UIViewController,presenting: UIViewController,source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        return PullDownAnimationController(transitionType: .presenting)
    }

    func animationController(forDismissed dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        return PullDownAnimationController(transitionType: .dismissing)
    }

    func presentationController(forPresented presented: UIViewController,presenting: UIViewController?,source: UIViewController) -> UIPresentationController? {
        return PresentationController(presentedViewController: presented,presenting: presenting)
    }

    func interactionControllerForPresentation(using animator: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
        return interactionController
    }

    func interactionControllerForDismissal(using animator: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
        return interactionController
    }

}

然后,您只需指定正在使用自定义转换以及应使用哪种转换委托.您可以在实例化目标视图控制器时执行此操作,也可以将其指定为目标视图控制器的init的一部分,例如：

class SecondViewController: UIViewController {

    let customTransitionDelegate = TransitioningDelegate()

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)

        modalPresentationStyle = .custom
        transitioningDelegate = customTransitionDelegate
    }

    ...
}

动画控制器指定动画的详细信息(如何设置动画,用于非交互式过渡的持续时间等)：

class PullDownAnimationController: NSObject,UIViewControllerAnimatedTransitioning {

    enum TransitionType {
        case presenting
        case dismissing
    }

    let transitionType: TransitionType

    init(transitionType: TransitionType) {
        self.transitionType = transitionType

        super.init()
    }

    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
        let inView   = transitionContext.containerView
        let toView   = transitionContext.view(forKey: .to)!
        let fromView = transitionContext.view(forKey: .from)!

        var frame = inView.bounds

        switch transitionType {
        case .presenting:
            frame.origin.y = -frame.size.height
            toView.frame = frame

            inView.addSubview(toView)
            UIView.animate(withDuration: transitionDuration(using: transitionContext),animations: {
                toView.frame = inView.bounds
            },completion: { finished in
                transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
            })
        case .dismissing:
            toView.frame = frame
            inView.insertSubview(toView,belowSubview: fromView)

            UIView.animate(withDuration: transitionDuration(using: transitionContext),animations: {
                frame.origin.y = -frame.size.height
                fromView.frame = frame
            },completion: { finished in
                transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
            })
        }
    }

    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        return 0.5
    }
}

上面的动画控制器处理呈现和解除,但如果感觉太复杂,理论上你可以将它分成两个类,一个用于呈现,另一个用于解雇.但我不喜欢有两个不同的类如此紧密耦合,所以我将承担animateTransition的轻微复杂性的成本,以确保它完全封装在一个类中.

无论如何,我们想要的下一个对象是表示控制器.在这种情况下,表示控制器告诉我们从视图层次结构中删除原始视图控制器的视图. (在这种情况下,我们这样做,因为您正在转换的场景碰巧占据整个屏幕,因此不需要在视图层次结构中保留旧视图.)如果您要添加任何其他额外的chrome(例如添加调光/模糊视图等),属于演示控制器.

无论如何,在这种情况下,演示控制器非常简单：

class PresentationController: UIPresentationController {
    override var shouldRemovePresentersView: Bool { return true }
}

最后,你可能想要一个手势识别器：

>实例化UIPercentDrivenInteractiveTransition;
>启动过渡本身;
>随着手势的进行,更新UIPercentDrivenInteractiveTransition;
>手势完成时取消或完成交互式转换;和
>完成后移除UIPercentDrivenInteractiveTransition(以确保它不会延迟,因此它不会干扰您以后可能要做的任何非交互式转换……这是一个很容易忽略的微妙的小点).

因此,“呈现”视图控制器可能具有可能执行以下操作的手势识别器：

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        let panDown = UIPanGestureRecognizer(target: self,action: #selector(handleGesture(_:)))
        view.addGestureRecognizer(panDown)
    }

    var interactionController: UIPercentDrivenInteractiveTransition?

    // pan down transitions to next view controller

    func handleGesture(_ gesture: UIPanGestureRecognizer) {
        let translate = gesture.translation(in: gesture.view)
        let percent   = translate.y / gesture.view!.bounds.size.height

        if gesture.state == .began {
            let controller = storyboard!.instantiateViewController(withIdentifier: "SecondViewController") as! SecondViewController
            interactionController = UIPercentDrivenInteractiveTransition()
            controller.customTransitionDelegate.interactionController = interactionController

            show(controller,sender: self)
        } else if gesture.state == .changed {
            interactionController?.update(percent)
        } else if gesture.state == .ended || gesture.state == .cancelled {
            let velocity = gesture.velocity(in: gesture.view)
            if (percent > 0.5 && velocity.y == 0) || velocity.y > 0 {
                interactionController?.finish()
            } else {
                interactionController?.cancel()
            }
            interactionController = nil
        }
    }

}

你可能也想改变它,所以它只能识别向下的手势(而不是任何旧的平底锅),但希望这说明了这个想法.

你可能希望“呈现”的视图控制器有一个手势识别器来解雇场景：

class SecondViewController: UIViewController {

    let customTransitionDelegate = TransitioningDelegate()

    required init?(coder aDecoder: NSCoder) {
        // as shown above
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        let panUp = UIPanGestureRecognizer(target: self,action: #selector(handleGesture(_:)))
        view.addGestureRecognizer(panUp)
    }

    // pan up transitions back to the presenting view controller

    var interactionController: UIPercentDrivenInteractiveTransition?

    func handleGesture(_ gesture: UIPanGestureRecognizer) {
        let translate = gesture.translation(in: gesture.view)
        let percent   = -translate.y / gesture.view!.bounds.size.height

        if gesture.state == .began {
            interactionController = UIPercentDrivenInteractiveTransition()
            customTransitionDelegate.interactionController = interactionController

            dismiss(animated: true)
        } else if gesture.state == .changed {
            interactionController?.update(percent)
        } else if gesture.state == .ended {
            let velocity = gesture.velocity(in: gesture.view)
            if (percent > 0.5 && velocity.y == 0) || velocity.y < 0 {
                interactionController?.finish()
            } else {
                interactionController?.cancel()
            }
            interactionController = nil
        }

    }

    @IBAction func didTapButton(_ sender: UIButton) {
        dismiss(animated: true)
    }

}

有关上述代码的演示,请参阅https://github.com/robertmryan/SwiftCustomTransitions.

看起来像：

但是,底线,自定义过渡有点复杂,所以我再次推荐你那些原创视频.在发布任何进一步的问题之前,请务必仔细观察它们.您的大多数问题都可能会在这些视频中得到解答.