透明与半透明 NavigationBar 切换的三种方案
https://www.jianshu.com/p/e3ca1b7b6cec
导航栏显示和隐藏的坑 - 简书
https://blog.csdn.net/lipengfei_1993/article/details/77564554
注意：标红的那个参数
- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
[self.navigationController setNavigationBarHidden:YES animated:animated];
}
- (void)viewWillDisappear:(BOOL)animated
{
[super viewWillDisappear:animated];
[self.navigationController setNavigationBarHidden:NO animated:animated];
}