CATransition* transition = [CATransition animation];
transition.type = kCATransitionPush;//可更改为其他方式
transition.subtype = kCATransitionFromLeft;//可更改为其他方式
transition.duration=0.15;
[self.navigationController.view.layer addAnimation:transition forKey:kCATransition];
[self.navigationController pushViewController:viewController animated:YES];

1. 如果楼主想要使用UINavigationController中的view controller stack，并且还想要同时自定义push、pop的动画效果，基本上是不可能的。原因在于想要使用view controller stack，就无法躲开
pushViewController:animated:这个方法，而一旦使用pushViewController:animated:，UINavigationController就会强制将要推入的viewController的frame设为当前可视区域的frame，从而断绝一切想要自定义动画的后路，例如如下代码，是不会产生任何效果的：

UINavigationController+CustomAnimation.h

@interface UINavigationController (CustomAnimation)

- (void)customPushViewController:(UIViewController *)viewController;

@end

UINavigationController+CustomAnimation.m

#import "UINavigationController+CustomAnimation.h"

- (void)customPushViewController:(UIViewController *)viewController
{
    viewController.view.frame = (CGRect){0, -viewController.view.frame.size.height, viewController.view.frame.size};
    [self pushViewController:viewController animated:NO];
    [UIView animateWithDuration:.15f
                     animations:^{
                         viewController.view.frame = (CGRect){0, 0, self.view.bounds.size};
                     }];
}

2. 如果仅仅是想添加自定义的push、pop动画，而不使用view controller stack，那么，如下代码就可以实现一个从上到下的push效果：

UINavigationController+CustomAnimation.h文件同上。

UINavigationController+CustomAnimation.m

#import "UINavigationController+CustomAnimation.h"
- (void)customPushViewController:(UIViewController *)viewController
{
    viewController.view.frame = (CGRect){0, -viewController.view.frame.size.height, viewController.view.frame.size};
    [self.topViewController.view addSubview:viewController.view];
    [UIView animateWithDuration:.15f
                     animations:^{
                         viewController.view.frame = (CGRect){0, 0, self.view.bounds.size};
                     }];
}