-(void)viewWillAppear:(BOOL)animated

{

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

    [super viewWillAppear:animated];

}

-(void)viewWillDisappear:(BOOL)animated

{

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

    [super viewWillDisappear:animated];

}

方法里的两行顺序不能颠倒，如果颠倒了就会导致 A页面隐藏了导航 push到B页面后 pop回A页面的过程中，导航立即隐藏 用户体验极差

隐藏NavigationBar的正确方式