当分离到从NSObject继承的自定义类时，TransitioningDelegate对UIPresentationController不起作用

Question

我使用自定义UIPresentationController与我自己的动画一起执行续集。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：

myDestinationController.transitioningDelegate = self

在我的self控制器中添加来自DBViewControllerTransitioningDelegate的2个方法一切正常。这两种方法都被称为。为什么？有什么区别？

Answer 1

  

transitioningDelegate中UIViewController的声明：

     

weak var transitioningDelegate: UIViewControllerTransitioningDelegate?

您可以看到transitioningDelegate持有weak引用。自定义TransitioningDelegate实例在您创建后立即发布，因为此处没有人拥有所有权。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。