View Controller转场

UINavigationControllerDelegate中相关方法

- (id<UIViewControllerAnimatedTransitioning>)
     navigationController:(UINavigationController *)navigationController
     animationControllerForOperation:(UINavigationControllerOperation)operation
     fromViewController:(UIViewController*)fromVC
     toViewController:(UIViewController*)toVC
{
     if (operation == UINavigationControllerOperationPush) {
          return self.animator;
     }
     return nil;
}