未为容器视图控制器调用的UIViewControllerTransitioningDelegate函数

Question

我正在以编程方式将View Controller的视图添加到容器视图，并希望它具有动画过渡，但是即使我调用了UIViewControllerTransitioningDelegate，也没有调用beginAppearanceTransition(animated:)函数。

let secondViewController = SecondViewController()
self.secondViewController = secondViewController
secondViewController.view.translatesAutoresizingMaskIntoConstraints = false
containerView.addSubview(secondViewController.view)
containerView.addConstraints(secondViewController.view.pinnedConstraints(view: containerView))
secondViewController.transitioningDelegate = self
secondViewController.modalPresentationStyle = .overCurrentContext
secondViewController.didMove(toParent: self)
secondViewController.beginAppearanceTransition(true, animated: true)

执行上述代码时，当前视图控制器中永远不会调用animationController(forPresented:presenting:source:) -> UIViewControllerAnimatedTransitioning?