iOS 系统自带磨玻璃代码

   UIBlurEffect * b = [UIBlurEffect effectWithStyle:UIBlurEffectStyleExtraLight];

    UIVisualEffectView * v = [[UIVisualEffectView alloc]initWithEffect:b];

    v.alpha = 0.5;

    v.frame = (CGRect){100,100,100,100};

    [self.view addSubview:v]