ios - pushViewController stuck or viewdidappear fail -

I'm just pushing this new VC like this.

  [nav pushViewController: vc animated: yes]; However, it does not push, the new scene reaches the state - the scene is visible but the viewer fails to reach some time. I can swipe back to return. I have tested the new scene frame and it is also normal. 
 
 See frame {{, 64}, {320, 455}} Do I know where the bug can be? 
 

Please check whether your UIViewController has been pushed or presented. If it is pushed then you can push a new UIViewController, then you can push the new view controller if it is presented, you can not push.