当分离到从 NSObject 继承的自定义类时，TransitioningDelegate 不适用于 UIPresentationController

Question

我使用自定义 UIPresentationController 来执行我自己的动画的续集。在prepareForSegue:

myDestinationController.transitioningDelegate = DBViewControllerTransitioningDelegate()
myDestinationController.modalPresentationStyle = .Custom

这是我的DBViewControllerTransitioningDelegate:

class DBViewControllerTransitioningDelegate: NSObject, UIViewControllerTransitioningDelegate {

    func presentationControllerForPresentedViewController(presented: UIViewController, presentingViewController presenting: UIViewController, sourceViewController source: UIViewController) -> UIPresentationController? {
        return DBOverlayPresentationController(presentedViewController: presented, presentingViewController: presenting)
    }

    func animationControllerForPresentedController(presented: UIViewController, presentingController presenting: UIViewController, sourceController source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        return DBTransitioningAnimator()
    }
}

它不起作用，因为没有调用方法。但是当我设置时：

myDestinationController.transitioningDelegate = self

在我的self 控制器中添加我的DBViewControllerTransitioningDelegate 中的2 个方法，一切都很好。这两种方法被调用。为什么？有什么区别？

Answer 1

在UIViewController 中声明transitioningDelegate：

weak var transitioningDelegate: UIViewControllerTransitioningDelegate?

如您所见，transitioningDelegate 持有 weak 引用。自定义的 TransitioningDelegate 实例在您创建后立即发布，因为这里没有人拥有所有权。当您在“控制器”中采用委托并将其分配给 transitioningDelegate 时，“某人”正在为您保留此委托实例。