iOS 导航栏pop的时候有块黑

导航栏被隐藏后pop的时候就会这样子，看着不开心☹️

解决：

- (void)viewWillAppear:(BOOL)animated{

    [super viewWillAppear:animated];

    [self.navigationController setNavigationBarHidden:YES animated:YES];

}

- (void)viewWillDisappear:(BOOL)animated{

    [super viewWillDisappear:animated];

    [self.navigationController setNavigationBarHidden:NO animated:YES];

}

接下来就如丝般顺滑😆

bug