这样写就不会出现，切换页面导航栏黑条问题了
-(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];
}