iOS navigationbar背景透明 左右按键显示最简方法

 [self.navigationController.navigationBar setHidden:NO];  

 self.navigationController.navigationBar.tintColor = [UIColor whiteColor]; 

 [self.navigationController.navigationBar setBackgroundImage:[UIImage new]forBarMetrics:UIBarMetricsDefault];     self.navigationController.navigationBar.shadowImage = [UIImage new];