iOS 导航栏设置透明，显示底部视图

//设置导航栏透明
[self.navigationController.navigationBar setTranslucent:true];
//把背景设为空
[self.navigationController.navigationBar setBackgroundImage:[UIImage new] forBarMetrics:UIBarMetricsDefault];
[self.navigationController.navigationBar setBackgroundColor:[UIColor clearColor]];
//处理导航栏有条线的问题
[self.navigationController.navigationBar setShadowImage:[UIImage new]];