用push，然后做出present的效果
ViewController*vc = [[ViewController alloc] init];
CATransition*transition = [CATransition animation];
transition.duration=0.25;
transition.timingFunction= [CAMediaTimingFunctionfunctionWithName:kCAMediaTimingFunctionDefault];
transition.type=kCATransitionPush;
transition.subtype=kCATransitionFromTop;
transition.delegate=self;
[self.navigationController.view.layer addAnimation:transitionforKey:nil];
self.navigationController.navigationBarHidden=YES;
[self.navigationController pushViewController:vc animated:NO];
