ios - 未调用 UIPageViewController 完成块

Question

当我打电话时

- (void)setViewControllers:(NSArray *)viewControllers 
                 direction:(UIPageViewControllerNavigationDirection)direction 
                  animated:(BOOL)animated 
                completion:(void (^)(BOOL finished))completion;

在UIPageViewController delegate

- (void)pageViewController:(UIPageViewController *)pageViewController 
        didFinishAnimating:(BOOL)finished 
   previousViewControllers:(NSArray *)previousViewControllers 
       transitionCompleted:(BOOL)completed;

我看到没有调用完成块。但是当我在方法之外调用这个方法时delegate，会调用完成块。我配置错了吗？你能给我提示吗！

谢谢！