-(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