ios开发让view保持在最上层

//将一个视图放在另一个视图上面
(void)insertSubview:(UIView )view belowSubview:(UIView )siblingSubview;
//将一个视图放在另一个视图下面
(void)insertSubview:(UIView )view aboveSubview:(UIView )siblingSubview;
//让view保持在最上层
(void)bringSubviewToFront:(UIView *)view;
//让view保持在最下层
(void)sendSubviewToBack:(UIView *)view;