添加蒙层：

UIView *view = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 320, 480)];    [view setTag:108];    [view setBackgroundColor:[UIColor blackColor]];    [view setAlpha:0.5];    [self.view addSubview:view];

删除

UIView *view = (UIView*)[self.view viewWithTag:108];    [view removeFromSuperview];

这个蒙层是会挡住你下面的view的，如果有button这些事件的话，则无法触发，解决的办法是：关闭view的userinteraction。

[view setUserInteractionEnabled:NO];