控制NavigationBar隐藏与否

在UINavigationControllerDelegate的方法中控制隐藏与否

- (void)navigationController:(UINavigationController *)navigationController willShowViewController:(UIViewController *)viewController animated:(BOOL)animated {
    BOOL shouldHidden = you logic here;
    [navigationController setNavigationBarHidden:shouldHidden
                                        animated:animated];
}