推送/弹出时UINavigationBar消失

Question

我使用method described here使用旧的（iOS7之前）推/动画动画：

@implementation UINavigationController (Retro)

- (void)pushViewControllerRetro:(UIViewController *)viewController {
    CATransition *transition = [CATransition animation];
    transition.duration = 0.25;
    transition.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];
    transition.type = kCATransitionPush;
    transition.subtype = kCATransitionFromRight;
    [self.view.layer addAnimation:transition forKey:nil];

    [self pushViewController:viewController animated:NO];
}

- (void)popViewControllerRetro {
    CATransition *transition = [CATransition animation];
    transition.duration = 0.25;
    transition.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];
    transition.type = kCATransitionPush;
    transition.subtype = kCATransitionFromLeft;
    [self.view.layer addAnimation:transition forKey:nil];

    [self popViewControllerAnimated:NO];
}

@end

我的问题是iOS7在推送新视图控制器时似乎淡化了前一个视图控制器的UINavigationBar。通常这看起来很好，因为iOS 7将视图拖到彼此之上。但是当我使用iOS7之前的动画时，它会给我一个短暂的闪光，因为导航栏会在新视图从右侧推入时消失。

有没有办法在导航栏上禁用淡入淡出动画？