- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    [self.navigationController setNavigationBarHidden:YES animated:animated];
}

- (void)viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated];

    if (!self.navigationController.presentedViewController&&![self.navigationController.transitionCoordinator isCancelled]) {
        [self.navigationController setNavigationBarHidden:NO animated:animated];
    }
}

- (void)viewDidDisappear:(BOOL)animated
{
    [super viewDidDisappear:animated];

    //MARK:偶尔在非常快速的从第二个页面取消拖返的时候，这里的输出会是 1 0 1 0。但是第二次的set hidden to no是有效的。
    //猜测可能是由于动画animated的原因，造成了第一次set hidden to no的还原。具体未知
    //所以我们在下一个runloop里去重新设置下应该就OK了
//    DLOG(@"1.hidden:%d",self.navigationController.navigationBarHidden);
    if (self.navigationController.navigationBarHidden) {
        [self.navigationController setNavigationBarHidden:NO animated:NO];
    }
//    DLOG(@"2.hidden:%d",self.navigationController.navigationBarHidden);
    dispatch_async(dispatch_get_main_queue(), ^{
//        DLOG(@"3.hidden:%d",self.navigationController.navigationBarHidden);
        if (self.navigationController.navigationBarHidden) {
            [self.navigationController setNavigationBarHidden:NO animated:NO];
        }
//        DLOG(@"4.hidden:%d",self.navigationController.navigationBarHidden);
    });
}