关于自定义转场动画的疑问

[一个小朋友]

rickytan，你好，我们项目中用到了这个库，目前在转场动画时遇见了问题：

我自定义一个类，遵守 UIViewControllerAnimatedTransitioning 协议 ，在当前UIViewController的

- (id<UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController animationControllerForOperation:(UINavigationControllerOperation)operation fromViewController:(UIViewController *)fromVC toViewController:(UIViewController *)toVC；

返回自定义类的实例对象，但在这类中只走

- (NSTimeInterval)transitionDuration:(id<UIViewControllerContextTransitioning>)transitionContext；

不走

- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext；

如果在UIViewController的

- (id<UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController animationControllerForOperation:(UINavigationControllerOperation)operation fromViewController:(UIViewController *)fromVC toViewController:(UIViewController *)toVC；

直接返回self，上面的两个代理方法都走。