控制器隐藏了导航 下页pop 导航位置看到黑条
解决：
-(void)viewWillDisappear:(BOOL)animated{
[super viewWillDisappear:animated];
[self.navigationController setNavigationBarHidden:NO animated:NO];
}
-(void)viewWillAppear:(BOOL)animated{
[super viewWillAppear:animated];
[self.navigationController setNavigationBarHidden:YES animated:YES];
}